OBX-5 in HL7 v2: A Field Guide to Observation Value
OBX-5 is the field everyone actually cares about — the result itself — but it has no fixed shape of its own; its meaning only makes sense once you already know what OBX-2 declared it to be.
OBX-5 is the fifth field of the HL7 v2 OBX segment — it carries the actual observation value, formatted according to whatever data type was declared in OBX-2, whether that is a number, a coded value, or free text.
What this field contains
Example
4.2 in OBX-5 is the numeric potassium value, valid only because OBX-2 declared this segment as NM. Synthetic result — not a real patient.
Where this trips people up
Long narrative results, like a radiology or pathology report, are frequently split across multiple repeating OBX segments because a single field or line has a practical length limit in some systems. Integrations that only read the first OBX-5 for a given report and never reassemble the rest end up storing a truncated impression, and nobody notices until a clinician opens the full report elsewhere and finds it cut off mid-sentence.