OBX Segment Structure
| Sno | Element Name | Len | Data type | Usage | Table |
| 1 | ID | 4 | SI | O | |
| 2 | Value Type | 2 | ID | C | 0125 |
| 3 | Observation Identifier | 250 | CE | R | |
| 4 | Observation Sub ID | 20 | ST | O | |
| 5 | Observation Value | 65536 | C | ||
| 6 | Units | 250 | CE | R | |
| 7 | Reference Ranges | 60 | ST | R | |
| 8 | Abnormal Flag | 5 | IS | R | 0078 |
| 9 | Probability | 5 | NM | O | |
| 10 | Nature of Abnormal Test | 2 | ID | O | 0080 |
| 11 | Observation Result Status | 1 | ID | R | 0085 |
| 12 | Date Last Observation | 26 | TS | O | |
| 13 | User defined Access Checks | 20 | ST | O | |
| 14 | Date/Time of Observation | 26 | TS | O | |
| 15 | Producer ID | 250 | CE | O | |
| 16 | Responsible Observer | 250 | XCN | O | |
| 17 | Observation Method | 250 | CE | O | |
| 18 | Equipment Instance Identifier | 22 | EI | O | |
| 19 | Date/Time of the Analysis | 26 | TS | O |
Usage Description:
| R | Required |
| RE | Required but may be Empty |
| O | Optional |
| C | Conditional |
| CE | Conditional but it may be empty |
| x | Not Supported |
OBX.1 – ID (SI)
This field contains the sequence number.
Examples:
OBX|1|NM|NA^Sodium^LA01^2951-2^Sodium^LN||140|mmol/L|135-146|N|||F||N|200807170527||RECHELTJ
OBX.2 – Value Type (ID)
This field contains the format of the observation value in OBX. Most Commonly Used values are
| CE | Coded Element |
| NM | Numeric |
| SN | Structured Numeric |
| ST | String Data |
| TX | Text Data |
| FT | Formatted text |
The Complete valid values for the value type of an observation are listed in HL7 Table 0125 as follows
| Value | Description |
| AD | Address |
| CE | Coded Entry |
| CF | Coded Element With Formatted Values |
| CK | Composite ID With Check Digit |
| CN | Composite ID And Name |
| CP | Composite Price |
| CX | Extended Composite ID With Check Digit |
| DT | Date |
| ED | Encapsulated Data |
| FT | Formatted Text (Display) |
| MO | Money |
| NM | Numeric |
| PN | Person Name |
| RP | Reference Pointer |
| SN | Structured Numeric |
| ST | String Data. |
| TM | Time |
| TN | Telephone Number |
| TS | Time Stamp (Date & Time) |
| TX | Text Data (Display) |
| XAD | Extended Address |
| XCN | Extended Composite Name And Number For Persons |
| XON | Extended Composite Name And Number For Organizations |
| XPN | Extended Person Number |
| XTN | Extended Telecommunications Number |
RP Reference pointer is used to Point to Image if the observation value is image.
Examples:
OBX|1|TX|OXY^OXID| ^F^D|-9.99|200 ug/ml|0.0-200||||F||2|201309250911||RBJ||
OBX|2|TX|2589M^KRATUM| ^D^E|||-||||N||4|201309240000||...||
OBX|3|ST|GLYCOHEM^Hemoglob A1C^LA01^4548-4^Hemoglob A1C^LN||6.8|% of total Hgb||H|||F|||200806250452||IF
OBX|4|NM|PT^Prothrombin Time^LA01^5902-2^Prothrombin Time^LN||12.1|seconds|11.8-14.3|N|||F||N|200806260829||IF
OBX|5|NM|1000714^TROPONIN I||0.0|NG/ML|0.0-0.2||||F|||20080628023100
OBX|6|ST|90020090^B MICRO DESCRIPTION^^90020090^B MICRO DESCRIPTION^||DNR||||||X|||20050923130500|CA^^L|||
OBX.3 - Observation identifier (CE)
This field contains a unique identifier for the observation (i.e., the individual test for which the result is reported in this OBX segment). The format is that of the Coded Element (CE). Example: 8625-6^P-R interval^LN.
The LOINC coding system must be used to represent the observation (test) identifier for results reported. HL7 permits senders to include both the Universal LOINC code and the local code for a given observation.For easy understanding, here we display the universal code in red and the local code in Blue as follows:
Please remember it is not necessary that LOINC Code should come first and followed by Local Code. Some lab will send in the reverse order.
LOINC Code^Print Text^LN^Local Code^Print Text^L
Element Format
CE Components: <identifier (ST)> ^ <text (ST)> ^ <name of coding system (IS)> ^ <alternate identifier (ST)> ^ <alternate text
(ST)> ^ <name of alternate coding system (IS)>
Please remember that not all the Lab system transmit the LOINC Code for the test observed. They may just use the internal Test code (alternate code) to represent the test.
| Component | Usage |
| identifier (ST) | R |
| text (ST) | R |
| name of coding system (IS) | R |
| alternate identifier (ST) | RE |
| alternate text (ST) | RE |
| name of alternate coding system (IS) | RE |
Examples:
2089-1^LDL Cholesterol^LN^576X^LDL Chol^L
[LOINC code for LDL Cholesterol, plus a lab-specific code]
7564ZZ^Hep B SAg^L
Lab-specific code for Hep B surface antigen, coded per lab’s
proprietary coding system; note that Hep.
CL^Chloride^LA01^2075-0^Chloride^LN
The above example, local code appear first and LOINC Code appear second (2075-0 IS LOINC Code for Chloride)
The following example contain only Local Code representation
OBX|1|NM|164858^Antinuclear Antibodies Direct^L||22|AU/mL|0-99|||N|F|20041222||200807311545|CB
OBX-8 Abnormal flags (IS)
We can extract the abnormal flag from this field i.e status of the result. The valid values are as follows
| Value | Description |
| L | Below Low Normal |
| H | Above High Normal |
| LL | Below lower panic limits |
| HH | Above upper panic limits |
| < | Below absolute low-off instrument scale |
| > | Above absolute high-off instrument scale |
| N | Normal (applies to non-numeric results) |
| A | Abnormal (applies to non-numeric results) |
| AA | Very abnormal (applies to non-numeric units, analogous to panic limits for numeric |
| U | Significant change up |
| D | Significant change down |
| B | Better--use when direction not relevant |
| W | Worse--use when direction not relevant |
| S | Susceptible. Indicates for microbiology susceptibilities only. |
| R | Resistant. Indicates for microbiology susceptibilities only. |
| I | Intermediate. Indicates for microbiology susceptibilities only. |
| MS | Moderately susceptible. Indicates for microbiology susceptibilities only. |
| VS | Very susceptible. Indicates for microbiology susceptibilities only |
Examples:
OBX|2|NM|35005420^PROTHROMBIN TIME^^35005420^PROTHROMBIN TIME^||23.8|Seconds||H|||F|||20090615165900|MH^^L|||
Results status change to Final. without retransmitting results already sent as ‘preliminary.’ E.g., radiology changes status from preliminary to final
OBX-11 Observation Result Status (ID)
This field contains the observation result status. Refer to HL7 table 0085 as follows
Value Description C Record coming over is a correction and thus replaces a final result D Deletes the OBX record F Final results; Can only be changed with a corrected result. I Specimen in lab; results pending P Preliminary results R Results entered -- not verified S Partial results X Results cannot be obtained for this observation U W Post original as wrong, e.g., transmitted for wrong patient
Examples:
OBX|10|NM|BCR^BUN / Creat Ratio^LA01^3097-3^BUN / Creat Ratio^LN||8||||||F||N|200807170527||RECHELTJ
Complete OBX Segment Examples:
OBX|1|NM|NA^Sodium^LA01^2951-2^Sodium^LN||140|mmol/L|135-146|N|||F||N|200807170527||RECHELTJ
OBX|2|NM|K^Potassium^LA01^2823-3^Potassium^LN||5.8|mmol/L|3.5-5.3|H|||F||N|200807170527||RECHELTJ
OBX|3|NM|CL^Chloride^LA01^2075-0^Chloride^LN||101|mmol/L|98-110|N|||F||N|200807170527||RECHELTJ
OBX|4|NM|CO2^CO2^LA01^2028-9^CO2^LN||23|mmol/L|21-33|N|||F||N|200807170527||RECHELTJ
OBX|5|NM|GAP^Anion Gap^LA01^X330373^Anion Gap^LN||16|mmol/L|3-16|N|||F||N|200807170527||RECHELTJ
OBX|6|NM|BUN^BUN^LA01^3094-0^BUN^LN||52|mg/dL|7-25|H|||F||N|200807170527||RECHELTJ
OBX|7|NM|CREAT^Creatinine^LA01^2160-0^Creatinine^LN||6.22|mg/dL|0.50-1.20|H|||F||N|200807170527||RECHELTJ
OBX|8|NM|GLU^Glucose^LA01^6777-7^Glucose^LN||101|mg/dL|65-99|H|||F||N|200807170527||RECHELTJ
OBX|9|NM|CA^Calcium^LA01^2000-8^Calcium^LN||7.2|mg/dL|8.6-10.2|L|||F||N|200807170527||RECHELTJ
OBX|10|NM|BCR^BUN / Creat Ratio^LA01^3097-3^BUN / Creat Ratio^LN||8||||||F||N|200807170527||RECHELTJ
OBX|11|NM|GFRAA^GFR MDRD Af Amer^LA01^X33914^GFR MDRD Af Amer^LN||8|See Note|||||F||N|200807170527||RECHELTJ
References:
1. What are LOINC Codes ?
2. HL7 Data Types
3. Complete set of LOINC codes and associated documentation