Step 4
Segments, one by one
MSH, PID, PV1, OBR, OBX. What each one says and where to find it.
A message is a stack of cards. Each card is a segment, and each segment has a precise role. Good news: a handful of segments covers the vast majority of messages. Let's tour the five you will see all the time, on the polysomnography message.
A sleep study report. The lab sends the hospital record an AHI of 28.5/h, flagged “high”: severe sleep apnea.
Click the color legend at the top of the editor to jump from one segment to another.
MSH, the envelope
Always first. It says who sends, to whom, when, and what type of message it is. If you could only read one segment to place a message, this would be it.
PID, the patient
The identity: name, date of birth, identifiers. This is where a system finds out who we are talking about, and files the information in the right record.
PV1, the visit
The care context: inpatient or outpatient, in which ward, under which doctor. PID says who; PV1 says under what circumstances.
OBR, the test
The order or report of a test: which test, ordered by whom, when. In a result, the OBR heads a group of measurements.
OBX, the result
One measurement, one value. The atomic brick: what, how much, in which unit, normal or not. A test often carries several OBX, one per measured parameter. In our message, the AHI, the minimum saturation and the conclusion are three OBX lines.
And all the others
There are dozens of other segments: NK1 (next of kin), AL1 (allergies),DG1 (diagnosis), ORC (order control), NTE (free note). You do not need to know them all. Spot the three-letter code, look up its role, and the segment reads like the others.