|
Chapter Chair/Editor: |
Clement J. McDonald, MD |
|
Chapter Chair/Editor: |
Hans Buitendijk |
|
Susan Rea Welch |
|
|
Editor: Product Experience |
J. Marc Overhage, MD |
|
Editor: Product Experience |
Robert Heiser |
|
Editor: Waveform Data |
Fritz Friedhoff |
|
Editor: Waveform Data |
Ernie Jacobs, MD |
|
Editor: Waveform Data |
Wayne Tracy |
|
Editor: Waveform Data |
Terry Lagerlund |
This chapter describes the transaction set required for sending structured patient-oriented clinical data from one computer system to another. A common use of these transaction sets will be to transmit observations and results of diagnostic studies from the producing system (e.g., clinical laboratory system, EKG system) (the filler), to the ordering system (e.g., HIS order entry, physician’s office system) (the placer). However, the transaction set is not limited to such transactions. Observations can be sent from producing systems to archival medical record systems (not necessarily the order placer) and from such medical record systems to other systems that were not part of the ordering loop, e.g., an office practice system of the referring physician for inpatient test results ordered by an inpatient surgeon. This chapter also provides mechanisms for registering clinical trials and methods for linking orders and results to clinical trials and for reporting experiences with drugs and devices.
These transaction sets permit the transmission of any kind of clinical observations including (but not limited to) clinical laboratory results, the results of imaging studies (excluding the image), EKG pulmonary function studies, measures of patient status and condition, vital signs, intake and output, severity and/or frequency of symptoms, drug allergies, problem lists, diagnostic lists, physician and nursing history, physicals, progress notes, operative notes and so on. These transaction sets carry information that is reported as text, numeric or categorical values. These messages do not carry the images themselves. (See ACR NEMA Publication 300-1988 Digital Imaging and Communications Standard, for image standards, and ASTM E1467.91 Standard specification for transferring digital neurophysiological data between independent computer systems, for transmitting EEG, EMG tracings).
An observation can be one of many data types. The main ones are text, numbers and codes. This provides the flexibility needed to transmit observations that are recorded as continuous values (e.g., glucose, diastolic blood pressure), as categorical values, e.g., patient position (sitting, reclining or standing), VDRL (reactive, weakly reactive or nonreactive), or as text. An entire History and Physical could be transmitted as an observation whose value is one large chunk of formatted text.
This chapter provides mechanisms for transmitting structured, record-oriented reports. This means that individual observations are transmitted as separate logical entities (objects), and within this entity, separate fields are defined for identifying the observation, its values, its units, normal ranges, etc., such that the receiving system can "understand," reorganize and/or react to the contents of these messages. Structured reports are to be distinguished from text-oriented reports which can also be transmitted via HL7 using the UDM message described in Chapter 2. The latter are ASCII images of nonstandard printed reports intended for display to humans. For practical purposes their contents are not understandable to the computer.
Observations may be transmitted in a solicited (in response to a query) or unsolicited mode. In the solicited mode, a user requests a set of observations according to criteria transmitted by the user. The sending system responds with existing data to satisfy the query (subject to access controls). Queries do not elicit new observations by the target system, they simply retrieve old observations. (See Chapter 2 for full discussion of the query transmission.)
The unsolicited mode is used primarily to transmit the values of new observations. It is the mode used by producing services to return the values of observations requested by an ordering system. A laboratory system, for example, would usually send the results of an AM electrolytes to the ordering HIS via the unsolicited mode. An intensive care system would send the blood pressures to the same HIS by the same mode. Calling such transactions unsolicited may sound like a misnomer, but is not. The placing service solicits the producing service to make the observation. It could also (through a query) solicit the value of that observation after it has been made. However, such an approach would demand continuous polling of the producing system until the result was produced. Using the unsolicited mode, the producing service returns the value of an observation as soon as it is available. The unsolicited mode can also be used to transmit new results to a system (e.g., an archival medical record system) that did not order the observation. The transactions that define these modes are more fully described in Section 7.2, "MESSAGE DEFINITIONS."
Observations are usually ordered and reported as sets (batteries) of many separate observations. Physicians order electrolytes (consisting of sodium, potassium, chloride, bicarbonate) or vitals (consisting of diastolic blood pressure, systolic blood pressure, pulse, and temperature). Moreover, tests that we may think of as single entity, e.g., cardiac echo, usually yield multiple separate measurements, e.g., left ventricular diameter, left atrial diameter, etc. Moreover, observations that are usually reported as text (e.g., the review of systems from the history and physical) can also be considered a set of separately analyzable units (e.g., cardiac history, pulmonary history, genito-urinary history, etc.). We strongly suggest that all text clinical reports be broken down into such separate analyzable entities and that these individual entities be transmitted as separate OBX segments. Because many attributes of a set of observations taken at one time will be identical, one OBR segment serves as a header for the report and carries the information that applies to all of the individual observations in the set. In the case of ordered observations, the OBR segment is a "turn-around document" like the manual request forms it replaces. It carries information about the order to the producing service; a copy of the OBR with additional fields completed is returned with the observations to the requesting service.
Not all observations are preceded by an order. However, all observations whether explicitly ordered or initiated without an order are reported with an OBR segment as the report header.
The major segments (OBR, OBX) defined in this chapter, their fields, and the code tables have been defined in collaboration with ASTM E31.11 with the goal of keeping HL7 observation transmission the same as ASTM E1238 in pursuit of the goals of ANSI HISPP and the Message Standards Developers Subcommittee. (Some sections of this chapter have been taken with permission directly from the E1238-91 document and vice versa in pursuit of those goals).
The OBR segment provides information that applies to all of the observations that follow. It includes a field that identifies a particular battery (or panel or set) of observations (e.g., electrolytes, vital signs or Admission H&P). For simplicity we will refer to the observation set as the battery. The battery usually corresponds to the entity that is ordered or performed as a unit. (In the case of a query, observation sets may be a more arbitrary collection of observations.) The OBX segment provides information about a single observation, and it includes a field that identifies that single observation (e.g., potassium, diastolic blood pressure or admission diagnosis). Both of these fields assume master tables that define coding systems (the universe of valid identifying codes) for batteries and observations, respectively. These tables will usually be part of the producing and sending services application and (usually) include many other useful pieces of information about the observation or battery. Segments for transmitting such master file information between systems that produce and systems that use clinical information are described in Chapter 8.
This Standard does not require the use of a particular coding system to identify either batteries or single observations In the past, local institutions tended to invent their own unique code systems for identifying test and other clinical observations because standard codes were not available. Such local code systems sufficed for transmitting information within the institutions but presented high barriers to pooling data from many sources for research or for building medical record systems. However, standard code systems such as LOINC and SNOMED now exist for many of these purposes, and we strongly encourage their use in observation reporting. These codes can be sent either as the only code or they can be sent along with the local historic code as the second code system in a CE code.
In past versions of the HL7 standard, Appendix A to Chapter 7 presented suggestions for constructing clinical codes from existing procedure code systems such as CPT4. Appendix A is now part of the Implementation Guide and contains LOINC codes for most laboratory tests and many common clinical variables (e.g., vital signs, intake and output, cardiovascular measurements and others). The most recent version of the LOINC database, which includes records for more than 7,000 observations and includes codes, names, synonyms and other attributes (such as the molecular weights of chemical moieties) for each observation, is available from the HL7 file server at http://dumccss.mc.duke.edu/standards/termcode/loinclab/loinc.html. The Implementation Guide provides construction rules for many variables that are not yet covered by LOINC. Codes for Neurophysiologic variables (EEG, EMG, Evoked potentials) are provided in Appendix X2 of ASTM E1467.
Some parts of this document (the discussion and tables defining units, the discussion of the rules of mapping observations to OBX segments, and some of the examples at the end of the chapter have been copied (with permission) from ASTM E1238.
As is true throughout this Standard, the emphasis should be on the abstract messages, defined without regard to the encoding rules. The example messages, however, are based upon the HL7 encoding rules.
GlossaryPerson or service that requests (places order for) an observation battery, e.g., the physician, the practice, clinic, or ward service, that orders a lab test, X-ray, vital signs, etc. The meaning is synonymous with, and used interchangeably with, requestor. See ORC-2-placer order number, Section 4.3.1.2, "Placer order number."
Person, or service, who produces the observations (fills the order) requested by the requestor. The word is synonymous with "producer" and includes diagnostic services and clinical services and care providers who report observations about their patients. The clinical laboratory is a producer of lab test results (filler of a lab order), the nursing service is the producer of vital signs observations (the filler of orders to measure vital signs), and so on. See ORC-3-filler order number, Section 4.3.1.3, "Filler order number."
A set of one or more observations identified as by a single name and code number, and treated as a shorthand unit for ordering or retrieving results of the constituent observations. In keeping with the mathematical conventions about set, a battery can be a single observation. Vital signs, electrolytes, routine admission tests, and obstetrical ultrasound are all examples. Vital signs (conventionally) consist of diastolic and systolic blood pressure, pulse, and respiratory rate. Electrolytes usually consist of Na+, K+, Cl-, and HCO3-. Routine admission tests might contain CBC, Electrolytes, SMA12, and Urinalysis. (Note that the elements of a battery for our purposes may also be batteries). Obstetrical ultrasound is a battery made up of traditional component measurements and the impression, all of which would be returned as separate results when returned to the requestor. A test involving waveform recording (such as an EKG) can be represented as a battery comprised of results of many categories, including digital waveform data, labels and annotations to the data, measurements, and the impression
The word battery is used in this specification synonymously with the word profile or panel. The individual observation elements within a battery may be characteristic of a physiologic system (e.g., liver function tests), or many different physiologic systems.
A measurement of a single variable or a single value derived logically and/or algebraically from other measured or derived values. A test result, a diastolic blood pressure, and a single chest X-ray impression are examples of observations. In certain circumstances, tracings and images may be treated by HL7 as individual observations and sent as a single OBX. These include waveform data described in Section 7.14, "WAVEFORM SUMMARY," and encapsulated data aggregates using the ED data type described in Section 2.8.14, "ED - encapsulated data," (which can represent actual images, audio data, etc.).
A typed aggregate of fields (fields) describing one complete aspect of a message. For example, the information about one order is sent as type of segment (OBR), the information related to an observation is sent as another segment (OBX).
The segment in a message is analogous to a record in a database, and in previous versions of the Standard we used record in place of the word segment. We have changed the nomenclature to be consistent with HL7 and other standards organizations in this version.
One specific attribute of a segment, for example, patient diagnosis, which may contain aggregates of fields further refining the basic attribute.
Some fields may contain many repeat fields. For example, the diagnoses field may contain many different diagnoses.
A field entry may also have discernible parts or components. For example, the patient’s name is recorded as last name, first name, and middle initial, each of which is a distinct entity separated by a component delimiter (sub-subfield in ASTM E1238-94).
Narrative reports from services such as Radiology usually consist of a number of subcomponents (e.g., a chest X-ray report may consist of a description, an impression, and a recommendation). Other studies, such as echocardiograms, contain analogous components, as well as numeric observations (e.g., left ventricular and diastolic diameter). Surgical pathology reports may contain information about multiple specimens and reports: the anatomic source, the gross description, the microscopic description, and a diagnostic impression for each specimen.
The current Standard treats each component of a narrative report as a separate "test" or observation. Just as a CHEM12 is transmitted as an order segment (OBR) plus 12 OBX segments, a chest X-ray would be transmitted as an order (OBR) segment plus three OBX segments, one for the description, one for the impression, and one for the recommendations. Similarly, an EKG report would be transmitted as an order segment (OBR), two OBX segments for the impression and recommendation, and additional OBX segments for each EKG measurement, e.g. the PR interval, QR interval, QRS axis, and so on.
We have defined code suffixes for constructing observation IDs for the common components of narrative reports (see Figure 7-1). The observation identifier for each such component is obtained by concatenating the observation battery ID (the ID in OBR-4-universal service ID of the preceding OBR from any coding system) with the appropriate suffix. The observation ID for a chest X-ray impression, for example, would be the chest X-ray observation ID (if CPT4, it would be 71020), a subcomponent delimiter, and the suffix, IMP, i.e., 71020&IMP.
This same combining rule applies to other coding systems including local and universal procedural codes (see Chapter 4). For example, if a local code for EKG was E793, and the locally agreed upon designation for that local code was EKG, the impression would be identified as E793&IMP^^99EKG.
Note:
The "99EKG" in the 3rd component is included to indicate a local code. The EKG's description, in this case, would be E793&GDT^^99EKG.Although it is strongly discouraged, the sender and receiver may agree to allow the omission of the observation ID component of a result segment when it is the same as the observation ID of the preceding OBR. In this case, only the ampersand and the suffix would have to be sent, e.g., &IMP or &REC, in OBX-3-observation identifier of a result segment. The full code would be assumed as the test identifier (recorded in the order segment) plus the category identifier recorded in the observation segment.
Figure 7-1. Observation ID suffices
|
Coded Results |
Suffix |
Type |
|
Diagnostic Impression |
IMP |
CE |
|
Recommendation |
REC |
CE |
|
Confirming procedures |
CNP |
CE |
|
Procedure Medication |
MED |
CE |
|
Anatomic Site |
ANT |
CE |
|
Device/Instrument |
DEV |
CE |
|
Serial # Device/Instrument |
SER |
ST |
|
Bulk Text Reports |
||
|
Gross Or General Description Of The Study |
GDT |
TX or FT |
|
Microscopic Or Secondary Description |
MDT |
TX or FT |
|
Technician's Comment |
TCM |
TX or FT |
|
Addendum Note |
ADT |
TX or FT |
|
Other |
||
|
Diagnosis Onset Date/Time |
ITM |
TS |
|
Diagnosis Resolution Date/Time |
RTM |
TS |
|
Comparison Study |
CMS |
CE |
|
Comparison Date/Time |
CMT |
TS |
|
Comparison Results |
CMR |
CE |
|
Comparison Change |
CMC |
CE |
|
Predicted Value |
PRD |
ST |
|
Percent Predicted |
PPR |
ST |
|
After Drug Observed |
AFD |
ST |
|
Predicted Value After Drug |
ADP |
ST |
|
Percent Predicted After Drug |
APP |
ST |
|
Timing Information |
TIM |
TS |
|
Channel Definition Data |
CHN |
CD |
|
Waveform Digital Data |
WAS |
NA or MA |
|
Waveform Annotation |
ANO |
CE |
The following subsections define each of the suffices except for the specialized waveform suffices, which are defined in Section 7.16, "WAVEFORM SPECIFIC OBSERVATION ID SUFFIXES."
When the suffix is IMP (OBX-3-observation identifier), the result is a diagnosis or finding, stored as a CE data type. Multiple result segments with an IMP suffix can be used if there are multiple parts to the study and each have an associated diagnosis (for example, the awake and sleep portion of an EEG). Each of these would have a different observation sub-ID. Multiple result segments with an IMP suffix can also be used if there are separate diagnoses corresponding to separate anatomic sites; in this case, the site for each diagnosis (each result segment with an IMP suffix) must be specified by an immediately preceding result segment with a suffix of ANT (see Section 7.1.3.5, "Anatomic site (ANT)"), which also has the same observation sub-ID. When multiple distinct diagnostic impressions are being reported, for example, mitral valve prolapse and aortic stenosis, each distinct impression should be sent in a separate OBX segment. More than one code may be included within one coded result segment, but only when such codes are modifiers of the principal impression, e.g., to report additional detail about the finding, not to report an entirely different finding. In this case, the OBX-5-observation value field may repeat, with each instance or repetition specifying one of the related coded impressions.
The coded data type for impressions does not mean that a reporting service must actually code all such impressions. The diagnostic impression can be sent as dictated text, but the text should be sent in the second component of the CE data type without a code to distinguish it from code, i.e. it should be preceded by a component delimiter, e.g.,
^congestive heart failure.When multiple separate text impressions are being reported, they should be reported in separate OBX segments to indicate that they are distinct impressions.
When the suffix is REC (OBX-3-observation identifier), the value is a CE result, representing the reading physician’s recommendations about repeat testing, follow up or therapy. For example, when an ambiguous lesion result is seen on a mammogram, the reading physician might recommend a repeat mammogram in six months, or a needle biopsy immediately. The recommended procedures are recorded as codes and/or text descriptions in the coded identifier structure.
If more than one follow up study is recommended, each such recommendation is sent in a separate REC.
The confirming procedure OBX suffix identifies additional studies used to confirm the diagnosis reported in the IMP OBX. If, for example, electron microscopy was done to confirm a surgical pathology diagnosis, the identifier for electron microscopy OBX-3-observation identifier would be stored as the value field of an observation ID with a confirming procedure suffix. Confirming procedures are most important in surgical pathology reports. But they might also be used by services such as endoscopy, to record the fact that a biopsy, culture, etc., was taken during the procedure. If more than one confirming procedure was used, each is sent in a separate result segment with observation ID suffix CNP.
A coded result segment with a suffix of MED (OBX-3-observation identifier) indicates that the segment contained information about medication given as part of the procedure -- contrast medication, medication intended to invoke a physiologic response (e.g., to be used in stress testing) or premedication. When patients receive more than one procedure medication, each medication should be reported in a separate OBX medication segment. If the transmitting system has codes available for medications, they would be recorded as the first component of OBX-3-observation identifier. The name and/or the dosages could be included in the second component of OBX-5-observation value.
A coded result segment with a suffix of MED (procedure medication) may also be used to define a medication administered during recording of digital waveform data or other extended diagnostic procedure, e.g., exercise test. These may be displayed by the receiving system overlaid with the other events reported. The procedure medication is assumed to pertain to and be associated with the data recorded at the time specified in OBX-14-date/time of the observation, of the OBX segment labeled with MED, when present.
Some diagnostic studies include observations about more than one anatomic site within one report. If, for example, a patient had an appendectomy incidental to gallbladder surgery, the pathologist’s assessment of both specimens would usually be included under a single specimen number in one report. Each distinct anatomic site would be reported as a separate OBX segment with a suffix of ANT (OBX-3-observation identifier). More than one coded anatomic location may be included within a single OBX segment only when such additional codes are used to construct an identity for a single site. In this case only, the OBX-5-observation value field may repeat, with each instance or repetition specifying one of the related locations. Each OBX segment with an ANT suffix could be followed by one or more OBX segments with an IMP or other suffix to transmit the diagnostic impression(s) associated with the anatomic site. These impressions or recommendations would be associated with a single anatomic site via a common observation ID.
When required, the instrument or device which generated an observation can be transmitted as an additional result of the study. In this case, the suffix of OBX-3-observation identifier is DEV. Examples include: an automated instrument in the laboratory; an imaging device and model number in radiology; or an automatic blood pressure machine on the ward. The device is specified as a coded entry in anticipation that these identifiers could be specified as codes. Initially, we expect that most of the information about devices will be transmitted as text in the second component of the CE identifier.
Vendor’s serial number of the device which generated the observation.
The general description suffix identifies the description component of a diagnostic study. In the case of anatomic pathology, it applies to the macroscopic (gross) description of the specimen. If the description consists of multiple paragraphs, the paragraphs should be separated by repeat delimiters so that the receiving computer can display them as paragraphs. It will not be necessary to include a description segment for a report when the impression segment says it all, e.g., for normal studies or studies such as EKG, whose reports are traditionally terse.
For most studies, a secondary description will not be needed. In the case of surgical pathology, however, the microscopic description is a separate part of the report. It describes the histology as seen through the microscope. The microscopic description will be sent in a segment with the suffix MDT in OBX-3-observation identifier. If the microscopic description consists of multiple paragraphs, the paragraphs should be separated by repeat delimiters so that the receiving computer can display them as paragraphs.
This is free text stored in a result segment whose OBX-3-observation identifier has a suffix of TCM for technician comment. It is used to record information about technical performance of the procedure, usually recorded by the technician.
Use to report information that is added as an addendum after the original dictation and sent as a separate labeled section of the report.
Use to record the date-time that a problem was first perceived to exist.
Use to record the date-time that a problem became inactive, i.e., the problem was cured or remitted.
When the reader of a diagnostic report compares the results for the current study with those of a previous study, this suffix allows them to report the nature of the comparison study as a separate result, i.e., an OBX segment with a segment whose observation ID has a suffix of CMS. Ordinarily, this would not be required because the observation ID in the other comparison OBX’s would identify the test, if any of the other comparison values were transmitted.
When the reader of a diagnostic procedure compares the current results with a previous study, this suffix allows them to report the date-time of the previous study (time optional) as a separate result within the current report.
When the reader of a diagnostic procedure compares the current results with those of a previous study on the same patient, this suffix allows them to report the results (impression) of the previous study as a discrete result within the current report.
When a diagnostic service reports a comparison between the current and a previous study, this suffix is used to report the degree of change (e.g., much worse, worse, minimal worsening, no change, slightly better, better, much better, returned to normal) as a separate result within the report.
In current dictation, information about comparison is usually contained in the descriptions of the study. The provision of the comparison suffixes listed above do not imply a requirement to send this information as separate components. The comparison variables are only meant to be enabling. When a system would like to transmit them as discrete report components, these suffixes give them the option.
When an observation has a predicted value as is the case for many spirometry tests, this suffix identifies the predicted observation as distinguished from the actual observation. The AS4 code for forced vital capacity is 94010.1 (see the HL7 Implementation Guide). The predicted forced vital capacity would be 94010.1&PRD.
This is a computed observation
= (actual observation)/(predicted observation. For forced vital capacity the percent predicted would be identified as 94010.1&PPR.An observation might be taken before and after a drug is given. This occurs especially in Spirometry. The predose observation is identified by the base ID. The post drug measure is identified by the AFD suffix. Using the AS4 base code for the forced vital capacity the post drug result would be identified by 94010.1&AFD.
The post drug predicted value is identified by the suffix, ADP. Following the pattern of the above example, it would be 94010.1&ADP.
The percent predicted after drug is identified by applying the suffix, APP to the base code -- 94010.1&APP if using the AS4 code for forced vital capacity.
This suffix is used only for transmitting waveform data. It is fully described in Section 7.16.1.
This suffix is used only for transmitting waveform data. It is fully described in Section 7.16.2.
This suffix is used only for transmitting waveform data. It is fully described in Section 7.16.3.
This suffix is used only for transmitting waveform data. It is fully described in Section 7.16.4.
In previous version of HL7, AS4 codes have been recommended for identifying clinical observations. The recently introduced LOINC codes (See Figure 7-2 for full information) may be more useful to many users. Code system information, including LOINC, has been moved from Appendix 7A to the Implementation Guide.
Various fields of data type CE which are used in segments defined both in the current chapter and other chapters, are used to transmit information about diagnoses, observation results, procedures, health outcomes, and drugs administered. Figures 7-2 and 7-3 (which were located in Chapter 2 in previous versions) list some common coding schemes for these types of information. The values in the second column of the table would be used in component 3 (and optionally, component 6) of a CE field to identify the coding scheme used.
Figure 7-2. Diagnostic coding schemes (from ASTM 1238-94 Table 3)
|
Name |
Code |
Source |
|
American College of Radiology finding codes |
ACR |
Index for Radiological Diagnosis Revised, 3rd Edition 1986, American College of Radiology, Reston, VA. |
|
AS4 Neurophysiology Codes |
AS4E |
ASTM’s diagnostic codes and test result coding/grading systems for clinical neurophysiology. See ASTM Specification E1467, Appendix 2. |
|
CEN ECG diagnostic codes |
CE |
CEN PT007. A quite comprehensive set of ECG diagnostic codes (abbreviations) and descriptions published as a pre-standard by CEN TC251. Available from CEN TC251 secretariat, c/o Georges DeMoor, State University Hospital Gent, De Pintelaan 185-5K3, 9000 Gent, Belgium or Jos Willems, University of Gathuisberg, 49 Herestraat, 3000 Leuven, Belgium. |
|
CLIP |
CLP |
Simon Leeming, Beth Israel Hospital, Boston MA. Codes for radiology reports. |
|
EUCLIDES |
E |
Available from Euclides Foundation International nv, Excelsiorlaan 4A, B-1930 Zaventem, Belgium; Phone: 32 2 720 90 60. |
|
Home Health Care |
HHC |
Home Health Care Classification System; Virginia Saba, EdD, RN; Geogetown University School of Nursing; Washington, DC. |
|
ICD9 |
I9 |
World Health Publications, Albany, NY. |
|
ICD9-CM |
I9C |
Commission on Professional and Hospital Activities, 1968 Green Rd., Ann Arbor, MI 48105. |
|
ICD-10 |
I10 |
World Health Publications, Albany, NY. |
|
International Classification of Diseases for Oncology |
ICDO |
International Classification of Diseases for Oncology, 2nd Edition. World Health Organization: Geneva, Switzerland, 1990. Order from: College of American Pathologists, 325 Waukegan Road, Northfield, IL, 60093-2750. (847) 446-8800. |
|
International Classification of Sleep Disorders |
ICSD |
International Classification of Sleep Disorders Diagnostic and Coding Manual, 1990, available from American Sleep Disorders Association, 604 Second Street SW, Rochester, MN 55902 |
|
Local general code |
99zzz or L |
Locally defined codes for purpose of sender or receiver. Local codes can be identified by L (for backward compatibility) or 99zzz (where z is an alphanumeric character). |
|
Local billing code |
LB |
Local billing codes/names (with extensions if needed). |
|
Omaha |
OHA |
Omaha Visiting Nurse Association, Omaha, NB. |
|
NANDA |
NDA |
North American Nursing Diagnosis Association, Philadelphia, PA. |
|
Read Classification |
RC |
The Read Clinical Classification of Medicine, Park View Surgery, 26 Leicester Rd., Loughborough LE11 2AG (includes drug procedure and other codes, as well as diagnostic codes). |
|
Systemized Nomenclature of Medicine (SNOMED) |
SNM |
Systemized Nomenclature of Medicine, 2nd Edition 1984 Vols 1, 2, College of American Pathologists, Skokie, IL. |
|
SNOMED International |
SNM3 |
SNOMED International, 1993 Vols 1-4, College of American Pathologists, Skokie, IL, 60077-1034.. |
|
SNOMED- DICOM Microglossary |
SDM |
College of American Pathologists, Skokie, IL, 60077-1034. (formerly designated as 99SDM). |
|
Unified Medical Language |
UML |
National Library of Medicine, 8600 Rockville Pike, Bethesda, MD 20894. |
Figure 7-3. Procedure/observation/drug ID/health outcomes coding systems
(From ASTM 1238-88 Table 5)|
Coding System |
Code |
Source/Description |
|
|
ASTM E1238/ E1467 Universal |
AS4 |
American Society for Testing & Materials and CPT4 (see Appendix X1 of Specification E1238 and Appendix X2 of Specification E1467). |
|
|
American Type Culture Collection |
ATC |
Reference cultures (microorganisms, tissue cultures, etc.), related biological materials and associated data. American Type Culture Collection, 12301 Parklawn Dr, Rockville MD, 20852. (301) 881-2600. http://www.atcc.org |
|
|
CPT-4 |
C4 |
American Medical Association, P.O. Box 10946, Chicago IL 60610. |
|
|
CPT-5 |
C5 |
(under development - same contact as above) |
|
|
CDC Surveillance |
CDS |
CDC Surveillance Codes. For data unique to specific public health surveillance requirements. Epidemiology Program Office, Centers for Disease Control and Prevention, 1600 Clifton Rd, Atlanta, GA, 30333. (404) 639-3661. |
|
|
DICOM Class Label |
DCL |
From the Message Standards Classes table of the SNOMED-DICOM-Microglossary. College of American Pathologists, Skokie, IL, 60077-1034 |
|
|
DICOM modality codes |
DCM |
Dean Bidgood, MD; Duke University Medical Center, Durham NC. Digital Imaging and Communications in Medicine (DICOM). From NEMA Publications PS-3.1 - PS 3.12: The ACR-NEMA DICOM Standard. National Electrical Manufacturers Association (NEMA). Rosslyn, VA, 22209., 1992, 1993, 1995 |
|
|
DICOM Query Label |
DQL |
HL7 Image Management Special Interest Group, Health Level Seven, Ann Arbor, MI. |
|
|
Enzyme Codes |
ENZC |
Enzyme Committee of the International Union of Biochemistry and Molecular Biology. Enzyme Nomenclature: Recommendations on the Nomenclature and Classification of Enzyme-Catalysed Reactions. London: Academic Press, 1992. |
|
|
EUCLIDES |
E |
AFP codes. Available from Euclides Foundation International nv, Excelsiorlaan 4A, B-1930 Zaventem, Belgium; Phone: 32 2 720 90 60. |
|
|
FDA K10 |
FDK |
Dept. of Health & Human Services, Food & Drug Administration, Rockville, MD 20857. (device & analyte process codes). |
|
|
HCFA Procedure Codes (HCPCS) |
HPC |
Health Care Financing Administration (HCFA) Common Procedure Coding System (HCPCS) including modifiers. |
|
|
ICD-10 Procedure Codes |
I10P |
Procedure Cosing System (ICD-10-PCS.) See http://www/hcfa.gov/stats/icd10.icd10.htm for more information. |
|
|
CDT-2 Codes |
CD2 |
American Dental Association’s Currenrt Dental Terminology (CDT-2) code. American Dental Association, 211 E. Chicago Avenue,. Chicago, Illinois 60611. |
|
|
POS Codes |
POS |
HCFA Place of Service Codes for Professional Claims (see http://www.hcfa.gov/medicare/poscode.htm). |
|
|
UPIN |
UPIN |
Medicare/HCFA's universal physician identification numbers, available from Health Care Financing Administration, U.S. Dept. of Health and Human Services, Bureau of Program Operations, 6325 Security Blvd., Meadows East Bldg., Room 300, Baltimore, MD 21207 |
|
|
Health Outcomes |
HI |
Health Outcomes Institute codes for outcome variables available (with responses) from Stratis Health (formerly Foundation for Health Care Evaluation and Health Outcomes Institute), 2901 Metro Drive, Suite 400, Bloomington, MN, 55425-1525; (612) 854-3306 (voice); (612) 853-8503 (fax); dziegen@winternet.com. See examples in the Implementation Guide. |
|
|
HIBCC |
HB |
Health Industry Business Communications Council, 5110 N. 40th St., Ste 120, Phoenix, AZ 85018. |
|
|
Home Health Care |
HHC |
Home Health Care Classification System; Virginia Saba, EdD, RN; Georgetown University School of Nursing; Washington, DC. |
|
|
Logical Observation Identifier Names and Codes (LOINC) |
LN |
Regenstrief Institute, c/o Kathy Hutchins, 1001 West 10th Street RG-5, Indianapolis, IN 46202. 317/630-7433. Also available via HL7 file server: FTP/Gopher (www.mcis.duke.edu/ standards/ termcode/loinclab and www.mcis.duke.edu/standards/termcode/loinclin) and World Wide Web (http:// www.mcis.duke.edu/ standards/termcode/ loincl.htm). January 1997version has identifiers, synonyms and cross-reference codes for reporting over 8,500 laboratory and related observations and 1,500 clinical measures. |
|
|
ICCS |
ICS |
Commission on Professional and Hospital Activities, 1968 Green Road, Ann Arbor, MI 48105. |
|
|
ICD-9CM |
I9C |
Commission on Professional and Hospital Activities, 1968 Green Road, Ann Arbor, MI 48105 (includes all procedures and diagnostic tests). |
|
|
ICHPPC-2 |
IC2 |
International Classification of Health Problems in Primary Care, Classification Committee of World Organization of National Colleges, Academies and Academic Associations of General Practitioners (WONCA), 3rd edition. An adaptation of ICD9 intended for use in General Medicine, Oxford University Press. |
|
|
ISBT |
IBT |
International Society of Blood Transfusion. Blood Group Terminology 1990. VOX Sanquines 1990 58(2):152-169. |
|
|
IUPAC/IFCC Property Codes |
IUC IUPP |
International Union of Pure and Applied Chemistry/International Federation of Clinical Chemistry. The Silver Book: Compendium of terminology and nomenclature of properties in clinical laboratory sciences. Oxford: Blackwell Scientific Publishers, 1995. Henrik Olesen, M.D., D.M.Sc., Chairperson, Department of Clinical Chemistry, KK76.4.2, Rigshospitalet, University Hospital of Copenhagen, DK-2200, Copenhagen. http://inet.uni-c.dk/~qukb7642/ |
|
|
IUPAC/IFCC Component Codes |
IUPC |
Codes used by IUPAC/IFF to identify the component (analyte) measured. Contact Henrik Olesen, as above for IUPP. |
|
|
Japanese Chemistry |
JC8 |
Clinical examination classification code. Japan Association of Clinical Pathology. Version 8, 1990. A multiaxial code including a subject code (e.g., Rubella = 5f395, identification code (e.g., virus ab IGG), a specimen code (e.g., serum =023) and a method code (e.g., ELISA = 022) |
|
|
Local |
99zzz or L |
Locally defined codes for purpose of sender or receiver. If multiple local codes exist, the format should be 99zzz, where z is an alphanumeric character. |
|
|
Medicare |
MCR |
Medicare billing codes/names. |
|
|
Medicaid |
MCD |
Medicaid billing codes/names. |
|
|
Nursing Interventions Classification |
NIC |
Iowa Intervention Project, College of Nursing, University of Iowa, Iowa City, Iowa |
|
|
National Provider Identifier |
NPI |
Health Care Finance Administration, US Dep’t. of Health and Human Services, 7500 Security Blcd., Baltimore, MD 21244. |
|
|
Omaha System |
OHA |
Omaha Visiting Nurse Association, Omaha, NB. |
|
|
UCDS |
UC |
Uniform Clinical Data Systems. Ms. Michael McMullan, Office of Peer Review Health Care Finance Administration, The Meadows East Bldg., 6325 Security Blvd., Baltimore, MD 21207; (301) 966 6851. |
|
|
Universal Product Code |
UPC |
The Uniform Code Council. 8163 Old Yankee Road, Suite J, Dayton, OH 45458; (513) 435 3070 |
|
|
Euclides Lab method codes |
E6 |
Available from Euclides Foundation International nv, Excelsiorlaan 4A, B-1930 Zaventem, Belgium; Phone: 32 2 720 90 60. |
|
|
Euclides Lab equipment codes |
E7 |
Available from Euclides Foundation International nv (see above) |
|
|
SNOMED topology codes (anatomic sites) |
SNT |
College of American Pathologists, 5202 Old Orchard Road, Skokie, IL 60077-1034. |
|
|
Euclides quantity codes |
E5 |
Available from Euclides Foundation International nv (see above) |
|
|
Drug codes: |
|||
|
CDC Vaccine Codes |
CVX |
National Immunization Program, Centers for Disease Control and Prevention, 1660 Clifton Road, Atlanta, GA, 30333 |
|
|
CDC Vaccine Manufacturer Codes |
MVX |
As above, for CVX |
|
|
CDC Methods/Instruments Codes |
CDCM |
Public Health Practice Program Office, Centers for Disease Control and Prevention, 4770 Buford Highway, Atlanta, GA, 30421. Also available via FTP: ftp.cdc.gov/pub/laboratory _info/CLIA and Gopher: gopher.cdc.gov:70/11/laboratory_info/CLIA |
|
|
CDC Analyte Codes |
CDCA |
As above, for CDCM |
|
|
First DataBank Drug Codes |
FDDC |
National Drug Data File. Proprietary product of First DataBank, Inc. (800) 633-3453, or http://www.firstdatabank.com. |
|
|
First DataBank Diagnostic Codes |
FDDX |
Used for drug-diagnosis interaction checking. Proprietary product of First DataBank, Inc. As above for FDDC. |
|
|
Medispan GPI |
MGPI |
Medispan hHierarchical drug codes for identifying drugs down to manufacturer and pill size. Proprietary product of MediSpan, Inc.l 8425 Woodfield Crossing Boulevard, Indianapolis, IN 46240. Tel: (800) 428-4495. |
|
|
Medispan Diagnostic Codes |
MDDX |
Codes Used for drug-diagnosis interaction checking. Proprietary product. Hierarchical drug codes for identifying drugs down to manufacturer and pill size. MediSpan, Inc.l 8425 Woodfield Crossing Boulevard, Indianapolis, IN 46240. Tel: (800) 428-4495. WWW: http://www.espan.com/medispan/pages/ medhome.html. As above for MGPI. |
|
|
Medical Economics Drug Codes |
MEDC |
Proprietary Codes for identifying drugs. Proprietary product of Medical Economics Data, Inc. (800) 223-0581. |
|
|
Medical Economics Diagnostic Codes |
MEDX |
Used for drug-diagnosis interaction checking. Proprietary product of Medical Economics Data, Inc. (800) 223-0581. |
|
|
Chemical abstract codes |
CAS |
These include unique codes for each unique chemical, including all generic drugs. The codes do not distinguish among different dosing forms. When multiple equivalent CAS numbers exist, use the first one listed in USAN. USAN 1990 and the USP dictionary of drug names, William M. Heller, Ph.D., Executive Editor, United States Pharmacopeial Convention, Inc., 12601 Twinbrook Parkway, Rockville, MD 20852. |
|
|
National drug codes |
NDC |
These provide unique codes for each distinct drug, dosing form, manufacturer, and packaging. (Available from the National Drug Code Directory, FDA, Rockville, MD, and other sources.) |
|
|
COSTART |
CST |
International coding system for adverse drug reactions. In the USA, maintained by the FDA, Rockville, MD. |
|
|
Medical Dictionary for Drug Regulatory Affairs (MEDDRA) |
MEDR |
Dr. Louise Wood, Medicines Control Agency, Market Towers, 1 Nine Elms Lane, London SW85NQ, UK Tel: (44)0 171-273-0000 WWW: http://www.open.gov.uk/mca/mcahome.htm |
|
|
WHO rec# drug codes |
W1, W2 |
World Health organization record number code. A unique sequential number is assigned to each unique single component drug and to each multi-component drug. Eight digits are allotted to each such code, six to identify the active agent, and 2 to identify the salt, of single content drugs. Six digits are assigned to each unique combination of drugs in a dispensing unit. The six digit code is identified by W1, the 8 digit code by W2. |
|
|
WHO rec# code with ASTM extension |
W4 |
With ASTM extensions (see Implementation Guide), the WHO codes can be used to report serum (and other) levels, patient compliance with drug usage instructions, average daily doses and more (see Appendix X1 the Implementation Guide). |
|
|
WHO ATC |
WC |
WHO's ATC codes provide a hierarchical classification of drugs by therapeutic class. They are linked to the record number codes listed above. |
|
|
WHO Adverse Reaction Terms |
ART |
WHO Collaborating Centre for International Drug Monitoring, Box 26, S-751 03, Uppsala, Sweden. |
|
Note: The Read and NLM (National Library of Medicine) codes in Table 3 also include drugs. A number of sources of unique drug names exist: British Approved Names (BAN), French-approved nonproprietary names (DCF), and International Nonproprietary name (INN). These sources are now being reviewed. Those that also provide unique codes will be added to the registry of coding sytems, using the abbreviations given in parentheses. |
|||
|
Device code: |
|||
|
MDNS |
UMD |
Universal Medical Device Nomenclature System. ECRI, 5200 Butler Pike, Plymouth Meeting, PA 19462 USA. Phone: 215-825-6000, Fax: 215-834-1275. |
|
The triggering events that follow are all served by the ORU (Observational report - Unsolicited) or the ORF (Observational Report Response) messages in combination with ACK and QRY. Each triggering event is listed below, along with the messages exchanged, and the segments that comprise the messages. The notation used to describe the sequence, optionality, and repeating of segments is described in Chapter 2, "Format for defining abstract messages."
ORU/ACK - unsolicited transmission of an observation message (event R01)With the type (OBX) defined in this chapter, and the OBR defined in Chapter 4, one can construct almost any clinical report as a three-level hierarchy, with the PID segment defined in Chapter 3 at the upper level, an order record (OBR) at the next level and one or more observation records (OBX) at the bottom.
One result segment (OBX) is transmitted for each component of a diagnostic report, such as an EKG or obstetrical ultrasound or electrolyte battery.
|
ORU^R01 |
Observational Results (Unsolicited) |
Chapter |
|
MSH |
Message Header |
2 |
|
{ |
||
|
[ |
||
|
PID |
Patient Identification |
3 |
|
[PD1] |
Additional Demographics |
3 |
|
[{NK1}] |
Next of Kin/Associated Parties |
3 |
|
[{NTE}] |
Notes and Comments |
2 |
|
[PV1 |
Patient Visit |
3 |
|
[PV2]] |
Patient Visit - Additional Info |
3 |
|
] |
||
|
{ |
||
|
[ORC] |
Order common |
4 |
|
OBR |
Observations Report ID |
7 |
|
{[NTE]} |
Notes and comments |
2 |
|
{ |
||
|
[OBX] |
Observation/Result |
7 |
|
{[NTE]} |
Notes and comments |
2 |
|
} |
||
|
{[CTI]} |
Clinical Trial Identification |
7 |
|
} |
||
|
} |
||
|
[DSC] |
Continuation Pointer |
2 |
|
ACK^R01 |
Acknowledgment |
Chapter |
|
MSH |
Message header |
2 |
|
MSA |
Message acknowledgment |
2 |
Note:
The ORC is permitted but not required in this message. Any information that could be included in either the ORC or the OBR must be included in the OBR on reporting. Notice also that the ORU (and the QRY) messages accommodate reports about many patients.Many report headers (OBR) may be sent beneath each patient segment, with many separate observation segments (OBX) beneath each OBR. Note segments (NTE) may be inserted after any of the above segments. The note segment applies to the entity that immediately precedes it, i.e., the patient if it follows the PID segment, the observation if it follows the OBR segment, and the individual result if it follows the OBX segment.
|
QRY^R02 |
Query |
Chapter |
|
MSH |
Message Header |
2 |
|
QRD |
Query Definition |
2 |
|
QRF |
Query Filter |
2 |
|
ORF^R04 |
Observational Report |
Chapter |
|
MSH |
Message Header |
2 |
|
MSA |
Message Acknowledgment |
2 |
|
QRD |
Query Definition |
2 |
|
[ QRF ] |
Query Filter |
2 |
|
{ [ PID |
Patient ID |
3 |
|
[{NTE}] ] |
Notes and Comments |
3 |
|
{ |
||
|
[ ORC ] |
Order common |
|
|
OBR |
Observation request |
7 |
|
{[NTE]} |
Notes and comments |
2 |
|
{ |
||
|
[OBX] |
Observation/Result |
7 |
|
{[NTE]} |
Notes and comments |
2 |
|
} |
||
|
{[CTI]} |
Clinical Trial Identification |
7 |
|
} } |
||
|
[ERR] |
Error |
2 |
|
[QAK] |
Query Acknowledgement |
2 |
|
[DSC] |
Continuation Pointer |
2 |
Display-oriented results reporting is described in Chapter 2, Section 2.14.1, "Display vs. record-oriented messages." The QRD and QRF segments are defined in Chapter 2, Section 2.24, "Messages Control Segments." Event R05 is used for queries for display results; event R06 is used in the unsolicited message for reporting display results.
The subject filters contained in the QRD and QRF segments are defined by local agreement between the inquiring system and the ancillary system.
The Set ID fields in the various segments (including PID) are used to count the number of segments of one kind transmitted at one level of the hierarchy.
The Query Result Level field of the QRD determines the amount of data requested. See Chapter 2, Section 2.24.4, "QRD - original style query definition segment."
The full definitions of many segments required for reporting clinical observations are included in other chapters. The patient identifying segment (PID) is provided in Chapter 3. The NTE segment is in Chapter 2.
OBR - observation request segmentIn the reporting of clinical data, the OBR serves as the report header. It identifies the observation set represented by the following atomic observations. It includes the relevant ordering information when that applies. It contains many of the attributes that usually apply to all of the included observations.
When a set of observations is ordered, the order message contains an OBR segment. However, observations can be collected and reported without an antecedent order. When observations are reported, the report message also includes one or more OBR segments. So, the OBR segment is like a turn-around document. Some fields in the OBR segment apply only to the ordering message and some to the reporting message. To those familiar with healthcare procedures, these should be obvious from their names (e.g., transcriptionist or principal result interpreter could only apply to the reporting phase). However, we have also flagged them in Figure 7-4 to indicate whether placer, filler, or both may send data in a given field.
Figure 7-4. OBR attributes
|
SEQ |
LEN |
DT |
OPT |
RP/# |
TBL# |
ITEM # |
ELEMENT NAME |
|
1 |
4 |
SI |
O |
00237 |
Set ID - OBR |
||
|
2 |
22 |
EI |
C |
00216 |
Placer Order Number |
||
|
3 |
22 |
EI |
C |
00217 |
Filler Order Number + |
||
|
4 |
200 |
CE |
R |
00238 |
Universal Service ID |
||
|
5 |
2 |
ID |
X |
00239 |
Priority |
||
|
6 |
26 |
TS |
X |
00240 |
Requested Date/Time |
||
|
7 |
26 |
TS |
C |
00241 |
Observation Date/Time # |
||
|
8 |
26 |
TS |
O |
00242 |
Observation End Date/Time # |
||
|
9 |
20 |
CQ |
O |
00243 |
Collection Volume * |
||
|
10 |
60 |
XCN |
O |
Y |
00244 |
Collector Identifier * |
|
|
11 |
1 |
ID |
O |
0065 |
00245 |
Specimen Action Code * |
|
|
12 |
60 |
CE |
O |
00246 |
Danger Code |
||
|
13 |
300 |
ST |
O |
00247 |
Relevant Clinical Info. |
||
|
14 |
26 |
TS |
C |
00248 |
Specimen Received Date/Time * |
||
|
15 |
300 |
CM |
O |
0070 |
00249 |
Specimen Source * |
|
|
16 |
80 |
XCN |
O |
Y |
00226 |
Ordering Provider |
|
|
17 |
40 |
XTN |
O |
Y/2 |
00250 |
Order Callback Phone Number |
|
|
18 |
60 |
ST |
O |
00251 |
Placer Field 1 |
||
|
19 |
60 |
ST |
O |
00252 |
Placer Field 2 |
||
|
20 |
60 |
ST |
O |
00253 |
Filler Field 1 + |
||
|
21 |
60 |
ST |
O |
00254 |
Filler Field 2 + |
||
|
22 |
26 |
TS |
C |
00255 |
Results Rpt/Status Chng - Date/Time + |
||
|
23 |
40 |
CM |
O |
00256 |
Charge to Practice + |
||
|
24 |
10 |
ID |
O |
0074 |
00257 |
Diagnostic Serv Sect ID |
|
|
25 |
1 |
ID |
C |
0123 |
00258 |
Result Status + |
|
|
26 |
400 |
CM |
O |
00259 |
Parent Result + |
||
|
27 |
200 |
TQ |
O |
Y |
00221 |
Quantity/Timing |
|
|
28 |
150 |
XCN |
O |
Y/5 |
00260 |
Result Copies To |
|
|
29 |
200 |
CM |
O |
00261 |
Parent * |
||
|
30 |
20 |
ID |
O |
0124 |
00262 |
Transportation Mode |
|
|
31 |
300 |
CE |
O |
Y |
00263 |
Reason for Study |
|
|
32 |
200 |
CM |
O |
00264 |
Principal Result Interpreter + |
||
|
33 |
200 |
CM |
O |
Y |
00265 |
Assistant Result Interpreter + |
|
|
34 |
200 |
CM |
O |
Y |
00266 |
Technician + |
|
|
35 |
200 |
CM |
O |
Y |
00267 |
Transcriptionist + |
|
|
36 |
26 |
TS |
O |
00268 |
Scheduled Date/Time + |
||
|
37 |
4 |
NM |
O |
01028 |
Number of Sample Containers * |
||
|
38 |
60 |
CE |
O |
Y |
01029 |
Transport Logistics of Collected Sample * |
|
|
39 |
200 |
CE |
O |
Y |
01030 |
Collector's Comment * |
|
|
40 |
60 |
CE |
O |
01031 |
Transport Arrangement Responsibility |
||
|
41 |
30 |
ID |
O |
0224 |
01032 |
Transport Arranged |
|
|
42 |
1 |
ID |
O |
0225 |
01033 |
Escort Required |
|
|
43 |
200 |
CE |
O |
Y |
01034 |
Planned Patient Transport Comment |
|
|
44 |
80 |
CE |
O |
0088 |
00393 |
Procedure Code |
|
|
45 |
80 |
CE |
O |
Y |
0340 |
01316 |
Procedure Code Modifier |
Note:
The complete description of these fields is provided below as well as in Chapter 4.The daggered (+) items in this segment are not created by the placer known to the filler, not the placer. They are created by the filler and valued as needed when the OBR segment is returned as part of a report. Hence on a new order sent to the filler, they are not valued. There is an exception when the filler initiates the order. In that case, the filler order number is valued and the placer order number may be blank. They are valued by the filler as needed when the OBR segment is returned as part of a report.
The starred (*) fields are only relevant when an observation is associated with a specimen. These are completed by the placer when the placer obtains the specimen. They are completed by the filler when the filler obtains the specimen.
OBR-7-observation date/time and OBR-8-observation end date/time (flagged with #) are the physiologically relevant times. In the case of an observation on a specimen, they represent the start and end of the specimen collection. In the case of an observation obtained directly from a subject (e.g., BP, Chest X-ray), they represent the start and end time of the observation.
Definition: For the first order transmitted, the sequence number shall be 1; for the second order, it shall be 2; and so on.
Components: <entity identifier (ST)> ^ <namespace ID (IS)> ^ <universal ID (ST)> ^ <universal ID type (ID)>
Definition: This field is a case of the Entity Identifier data type (See 2.8.13, "EI - Entity identifier"). The first component is a string that identifies an individual order (e.g., OBR). A limit of fifteen (15) characters is suggested but not required. It is assigned by the place (ordering application). It identifies an order uniquely among all orders from a particular ordering application. The second through fourth components contain the application ID of the placing application in the same form as the HD data type (Section 2.8.18, "HD - Hierarchic designator"). The second component, namespace ID, is a user-defined coded value that will be uniquely associated with an application. A limit of six (6) characters is suggested but not required. A given institution or group of intercommunicating institutions should establish a unique list of applications that may be potential placers and fillers and assign unique application IDs. The components are separated by component delimiters.
There are three situations in which the true placer is somewhat arbitrary (and thus not unique):