What LOINC is

LOINC is a common language (set of identifiers, names, and codes) for identifying health measurements, observations, and documents. If you think of an observation as a "question" and the observation result value as an "answer."

LOINC codes represent the “question” for a test or measurement

Where needed, codes from other standards (e.g. SNOMED CT) represent the “answer.” Of course, you don't always need a code for the result value. For quantitative results, the "answer" is just the numeric value—with its associated units of measure.

Most laboratory and clinical systems today are sending data out using the HL7 version 2 messaging standard. Looking at an example of the place in the HL7 message where the test results go, you can see how a LOINC code identifies the question and a SNOMED CT code represents the answer:

Coded Results in an HL7 message

Related: Common questions about LOINC and other data standards

Sending local test codes and names along with LOINC codes

We think it is always a good idea to send your local concept identifier and name along with codes from a vocabulary standard. It makes troubleshooting a whole lot easier! Fortunately, this is easy to do within the HL7 message standard. The OBX-3 slot allows 2 sets of triplets, one for your local concept and one for the concept from the vocabulary standard:

Local code and LOINC code in a numeric result message

Related: Watch a presentation on HL7 standards