HL7 SI Sequence ID
HL7 datatype components SI components from HL7 v2.5.1 Hide components
These are the generated components for the version selected at the top of the page. The article stays practical, and this panel follows the chosen HL7 version.
Components
SI is a sequence ID. It is a simple ordinal number used to keep repetitions or related rows in order, not a business identifier.
In this guide, SI appears in AFF.1, AIG.1, AIL.1, AIP.1, AIS.1, AL1.1 and related fields. That used-by list is a good reality check: the datatype is only half the story, and the field that uses it tells you the workflow.
The component panel above is expanded by default because most datatype pages are used as quick lookup pages. Start there for the exact HL7 v2.5.1 shape, then use the notes below for the practical gotchas.
The Value
SI is primitive in this v2.5.1 reference data, so there are no caret-separated components to expand. The whole field value is the datatype value. That makes it quick to read, but it also means validation has to happen at the field level: the datatype will not give you extra components to explain what the value means.
Practical Notes
Keep numeric values numeric. Do not mix display formatting, unit text, or currency labels into the number component when the datatype has a separate place for that meaning. A format validator for whole numbers or decimals is a simple way to catch this before the receiving system has to complain.
In HL7 Soup Web, click a field that uses SI to see the field meaning beside the raw value. For primitive datatypes, that quick field-level check is usually more useful than looking for components that do not exist.
Official and Reference Notes
For formal reference, compare the generated HL7 v2.5.1 panel above with the HL7 v2.5.1 datatype list and the HL7 Terminology data type code system. Local implementation guides can narrow allowed values, tables, and component usage.