LOINC is a code system (i.e., set of identifiers, names, and codes) for clinical and laboratory observations, health care screening/survey instruments, and document type identifiers. Each LOINC record corresponds to a single observation of almost any type (i.e., observables) and is best known for concepts that represent laboratory tests. LOINC also includes representation of document types and thus, frequently represents a document section in consolidated clinical document architecture (C-CDA) and other templated exchange standards. There is no intent for LOINC codes to transmit all possible information about a test or observation; the intent is only to identify the observations. The LOINC code for a name is unique and permanent. Systems should always transmit LOINC codes with a hyphen before the check digit (e.g., 10154-3) and transmit the numeric code as a variable length number, without leading zeros. LOINC codes are available for commercial use without charge, subject to the terms of a license that assures the integrity and ownership of the codes.

Special Situations with LOINC Survey/Evaluation Tools

Measure developers can use LOINC to represent survey instrument questions (observations). In survey instruments, there is tight alignment between the question and the acceptable set of answers. Because of this, LOINC often also includes specific answer sets for the survey questions, called LOINC Answers (LA codes). When defining the set of answers specifically within the survey, the LA set is normative, which means only the specified LA codes are acceptable responses (values) for that LOINC observable. Defined normative LA sets can occur anywhere in LOINC, and because they are a requirement when defined, users of LOINC must look for and respect these restrictions.

Assignment of a LOINC code to most LOINC survey/evaluation tools for the overall tool is a type of LOINC Panel because that is the LOINC construct that collects other LOINC codes used together. In addition, LOINC curators assign a different LOINC code for each evaluation question/observation included in the survey or evaluation tool. In some cases, the LOINC survey will reuse observations defined in a different (usually related) survey. In many cases, the LOINC survey will include information on the ownership of the survey and indicate whether the individual observations are copyright protected and whether survey users can use the independent observations outside of the complete survey instrument as a complete questionnaire.

Many survey instruments include summary final scores (i.e., a LOINC observation) based on a sum of the values associated with the specified LA codes allowed for all the component questions. The measure developer should consider all elements of a LOINC tool before use and take care when using LOINC observables with specified answer codes to determine whether there is a requirement for use of the LA codes of that set.

A measure developer may need to request new LOINC concepts and can find instructions and tools to request LOINC concepts on the LOINC website. Measure developers should account for contractual timelines when considering applying for new concepts.