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:
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:
