What is HL7?

Reading the Standard

The standard specifies optional segments with square braces [ ] and repeating segments with curly braces { }

Here is what you would typically read in the standard:

And this table explains what the column headings mean:

Label What it means
Description/Name Description of the field.
Item # – ID Number A small integer that uniquely identifies the data item throughout.
Segment What segment you can find the field in.
Seq # or Position The field number to locate the data in.
Len – Normative Length If applicable the number of characters that one occurrence of the data field or component may occupy if populated.
C.Len – Conformance Length

If populated, the conformance length column specifies the minimum length that applications must be able to store.

In addition, the conformance length may be followed by a “=” or a “#”. The “=” denotes the value may never be truncated, and the “#” denotes that the truncation behaviour defined for the data type applies.

DT – Data Type Type of data referenced in.
OPT – Optionality Whether the field is required, optional, or conditional in a segment.
RP/# – Repetition Whether a field may repeatY = Yes / N = No
Table Some fields have tables of recommended or mandatory codes. The field references the table number with the specification for easy reference. Optionality can be defined by the following identifiers:

R = Required

RE = Required/may be empty

O = Optional

C = Conditional on field/Event

X = Not Used

B = Backwards compatibility

W = Withdrawn

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