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LOINC is a coding system for lab tests, but also for surveys, tests and other clinical procedures or activities that create a result, usually for a diagnostic purpose.


All LOINC source information is obtained from the LOINC websites that is supported by the Regenstrief institute, except the mapping between LOINC and CPT4, which is provided by the NLM: Generic LOINC Concept

  1. LOINC Multiaxial Hierarchy
  2. LOINC Forms and LOINC Answers
  3. LOINC Panel
  4. LOINC Class
  5. LOINC to CPT mapping
  6. LOINC to SNOMED mapping

Standard Concepts

All LOINC Concepts are Standard Concepts, while Concepts of the Source LOINC Class, LOINC Hierarchy are Classification Concepts.

Concept Classes

Concepts in the LOINC vocabulary are assigned Concept Class as following:

SourceResourcedConcept ClassDescription
LOINCCLASSTYPE=1Lab TestThe Universal Lab Order Codes Value Set contains the most frequent lab orders
CLASSTYPE=2Clinical ObservationAnything that can be tested, measured, or observed about a patient without removing a specimen
CLASSTYPE=3Claims AttachmentInformation necessary to adjudicate claims for ambulance, rehabilitation, or emergency room services
CLASSTYPE=4SurveySet of questions on a survey or form
CLASSLOINC ClassSimilar to the Concept Classes of each LOINC Concept, but more detailed and hierarchical
LOINC HierarchyCODELOINC HierarchySimilar to LOINC Class, but separate hierarchical system
LOINC AnswerAnswerStringIDAnswerObservation result value as an answer to a LOINC Concept


LOINC Concepts can have a Measurement or Observation Domain. This is assigned as following:

SourceDepending on Domain
LOINCCLASSTYPE=1 or 2Measurement
CLASSTYPE=3 or 4Observation
LOINC HierarchyConcept_code>'LP76352-1'Observation
LOINC ClassManualObservation or Measurement
LOINC Answer Meas Value


Relationships are defined within LOINC and between LOINC and CPT and LOINC and SNOMED:

Internal LOINC relationships

  1. “Is a” relationships between LOINC Concepts and LOINC Hierarchy and LOINC Class Concepts
  2. “Has Answer” relationships between LOINC Concepts and LOINC Answer Concepts
  3. “Panel contains” relationships between LOINC Concepts

LOINC to SNOMED relationships

These relationships are defined as “LOINC - SNOMED eq” between “LOINC Hierarchy” Concepts and SNOMED Concepts representing the entity that is measured. Note that only a small fraction (1% as of late 2015) are currently mapped. Also, note that some of the mappings seem to confuse the testing for drugs with the drugs themselves.

LOINC to CPT relationships

These relationships are defined as “LOINC - CPT4 eq” between LOINC Lab Test Concepts and SNOMED Concepts. Note that only a small franction (2% as of late 2015) are mapped.


All internal “Is a” and “Panel contains” relationships participate in the creation of the CONCEPT_ANCESTOR table, creating an internal hierarchy within LOINC not connected to the larger Measurement or Observation Domain space.

documentation/vocabulary/loinc.txt · Last modified: 2015/10/11 22:00 by cgreich