HL7 OBX – Observation Segment

The OBX segment is primarily used to carry key clinical observation/results reporting information within report messages, which must be transmitted back to the requesting system, to another physician system (such as a referring physician or office practice system), or to an archival medical record system. In certain cases (such as ORM messages), the OBX segment may carry clinical information that might be needed by the receiving system to interpret the observation to be made, rather than actual information about observations and results.

The OBX segment is part of multiple message types that transmit patient clinical information. However this segment is most commonly utilized in ORU (Observational Report – Unsolicited) messages, and is sometimes utilized in ORM (Order) and ADT (Admit Discharge Transfer) messages. The OBX segment transmits a single observation or observation fragment, and can be used more than once in the message.

The fields in the OBX segment are as follows:

SEQ LEN DT OPT RP/# ELEMENT NAME
1 4 SI O   Set ID – Obx
2 2 ID R   Value Type
3 590 CE R   Observation Identifier
4 20 ST O   Observation Sub-Id
5 65536 ST O   Observation Value
6 60 CE O   Units
7 10 ST O   Reference Range
8 5 ID O Y/5 Abnormal Flags
9 5 NM O   Probability
10 2 ID O   Nature of Abnormal Test
11 1 ID R   Observ Result Status
12 26 TS O   Data Last Obs Normal Values
13 20 ST O   User Defined Access Checks
14 26 TS O   Date/Time of the Observation
15 60 CE O   Producer’s Id
16 80 XCN O   Responsible Observer
17 80 CE O Y Observation Method

*Note: For the complete HL7 Standard, please go to the HL7 organization website.

OBX segments may, optionally, be followed by the NTE segment to provide notes and comments. In HL7 pipe and hat format, the OBX segments (shown in red below) would look like this in an ORU-R01 message. In this example, the first OBX segment does not have any notes or comments, while the next three OBX segments do:


MSH|^~\&|LCS|LCA|LIS|TEST9999|199807311532||ORU^R01|3630|P|2.2
PID|3|2161348473|20923085580|01572633|20923085580^TESTPAT||19730204|
M|||^^^^00000-0000|||||||86427531^^^03|SSN# HERE
PV1||I|^802^1||||8625^Physician^Michael|86-7468^||xxx|||||||||V1001
ORC|NW|8642753100013^LIS|20923085580^LCS||||||19980728000000|||PEED
OBR|1|8642753100013^LIS|20923085580^LCS|083824^PANEL 083824^L|||19980728083600|||||| CH13380|19980728000000||||||20923085580||19980730041800|||F
OBX|1|NM|150001^HIV-1 ABS-O.D. RATIO^L|||||||N|X
OBX|2|CE|001719^HIV-1 ABS, SEMI-QN^L||HTN|||||N|F|19910123|| 19980729155700|BN

NTE|1|L|Result: NEGATIVE by EIA screen.
NTE|2|L|No antibodies to HIV-1 detected.
OBX|3|CE|169999^.^L||SPRCS|||||N|F|||19980728130600|BN
NTE|1|L|NOTE: Submission of serum
NTE|2|L|separator tube recommended
NTE|3|L|for this test. Thank you
NTE|4|L|for your cooperation if you
NTE|5|L|are already doing so.
OBX|4|CE|169998^.^L||SPRCS|||||N|F|||19980728130600|BN
ZPS|1|BN|LABCORP HOLDINGS|1447 YORK COURT^^BURLINGTON^NC^272152230|8007624344