How to use these specifications

Start by searching for the thing you want. The rest of this page shows what you get when you land on it.

If you want to read a whole message instead, how to read an HL7 v2 message takes one apart line by line.

1. Search for anything

Press / on any page. Type a segment code, a field like PID-5, a data type or a table number. Arrow keys move, Enter opens.

The search box open with PID-5 typed, showing the Patient Name field as a result — Searching `PID-5` opens the field itself, not the top of the PID page.

2. A segment page

Search a segment code and you get the page for that segment. Every one ends with a table of its fields. Four columns are links:

DTthe data type. Opens the panel showing what is inside the field.
TBL#the code table the field takes its values from.
OPTthe heading itself. Explains what R, O, C and B mean.
CARDINALITYthe heading explains how 0..1 and 1..* are worked out.

A field number with a dotted underline has components inside it. Click the number to see them without leaving the page.

The PID field table, with the data type, table number, OPT and CARDINALITY columns as links — The 7 busiest segments also carry a worked message, notes on the fields that cause trouble, and a FHIR mapping.

3. A message type page

Search ADT and you get the message type. The page tells you what goes in MSH-9. It then draws each structure as a tree, so you can see which segments the message carries and which of them you have to send.

An ADT message structure drawn as a tree of segments, with required ones marked R — A segment marked `R` inside a group is required only if you send that group.

4. A data type

Search a data type, or click one in the DT column, and it opens on the data types page. You get a diagram of the parts in order, a worked example, and the full component table.

The CX data type open, showing its parts in order and its component table — Opening another closes this one, so the page never grows under you.

5. A code table

Search a table number and you get its values. The badge says whether the standard fixes the list or only suggests it, which decides whether an unknown code is an error.

Table 0004 open, showing its nine patient class values — The page also names the segments that bind a field to this table.

6. A chapter

The standard is split into chapters by subject. A chapter page lists the segments, trigger events and message types defined in it, so you can work through one subject at a time.

Chapter 03, Patient Administration, listing the segments defined in it — Chapter 03 is patient administration, chapter 04 is orders, chapter 07 is results.

7. Browsing instead of searching

The tabs along the top are the five complete lists. The sidebar lists the segments and message types you will meet most often, and it is on every page.

The sidebar beside a segment page, listing the common segments and message types — On a narrow screen the sidebar moves behind a button at the top.

The long lists carry a chapter filter at the top right. Tick a chapter to see only what belongs to it.

The chapter filter open, listing the chapters with a checkbox beside each — Tick more than one to see them together.

8. Internal linking

The standard keeps a field, its data type, its table and the messages that carry it in four different chapters. Here they are one click apart, both ways:

Fieldslink to their data type and their table.
Tablesname the segments that use them.
Segmentslist the message types that carry them.
Termsa word with a dotted underline is in the glossary. Hover to read it where you are.

9. Open a message in HL7 Studio

The 7 segments that are written up carry a real message. Open it in HL7 Studio and you get that message, not a generic sample.

The link that opens the worked message in HL7 Studio — Change any value and the parse updates as you type.

That is the whole interface. Next: how to read an HL7 v2 message, or the 151 segments.