LOINCLogical Observation Identifiers Names and Codes

What it is

LOINC is a common language (identifiers, names and codes) for identifying health measurements, observations and documents. It covers laboratory tests, clinical measures such as vital signs and anthropometrics, standardized survey instruments, and panels, forms and documents. It was started in 1994 by Clem McDonald, then an investigator at the Regenstrief Institute, because laboratories sent their results over HL7 with internal codes that the receiving system could not interpret without a map for each source.

How it is built

A LOINC code is a number, a dash and a check digit, for example 806-0. The code has no meaning of its own and is permanent. Its fully specified name combines six parts:

So 806-0 is a manual count of leukocytes in cerebrospinal fluid. Each part has its own code with an "LP" prefix, which makes translation easier.

Versions and licence

As of October 2026, the current version is 2.83, released on 19 August 2026. Regenstrief releases two versions a year, in February and August, and has announced a move to monthly releases in 2027.

The licence allows LOINC to be used, copied and distributed without licence fees or royalties, for commercial or non-commercial purposes. It forbids using it to develop a different standard for identifying observations and changing the contents of its fields; local codes that are added must start with "X".

Common misconceptions

• LOINC identifies the question, not the answer. The value can be a number with units, and qualitative results are often coded with SNOMED CT.
• It is not for diagnoses or for billing procedures: that is what ICD and, in the US, CPT are for.
• It does not force you to drop local codes. HL7 v2 and FHIR allow sending the local code and the LOINC code together.
• Mapping a laboratory catalogue to LOINC is expert work: the same test name can correspond to different codes depending on the specimen, scale or method.