Regenstrief InstituteLogical Observation Identifiers Names and Codes (LOINC) is one of the most widely adopted standards in health informatics, providing a universal coding system for identifying laboratory tests, clinical observations, survey instruments, and clinical document types. With over 100,000 terms, LOINC serves as the common language enabling electronic health record systems worldwide to exchange clinical results consistently and accurately.
Background
LOINC was created in 1994 by the Regenstrief Institute, a nonprofit medical research organization in Indianapolis, Indiana. The standard emerged in response to the demand for an electronic clinical care and management database that could facilitate the exchange of laboratory results between different healthcare systems. At the time, the same laboratory test might have dozens of different proprietary codes across different hospitals and laboratories, making it nearly impossible to aggregate or compare results electronically.
The standard has grown significantly since its inception. Originally focused on laboratory test identifiers, LOINC has expanded to cover nursing diagnoses, nursing interventions, outcomes classification, patient care data sets, clinical document types, and standardized survey instruments such as the PHQ-9 depression scale and Glasgow Coma Score.
Purpose & Scope
LOINC provides universal code names and identifiers for medical terminology related to electronic health records. Its purpose is to enable the electronic exchange and gathering of clinical results across healthcare networks. The standard has two main divisions:
| Division | Coverage |
|---|---|
| Laboratory LOINC | Laboratory tests, microbiology tests, antibiotic susceptibilities |
| Clinical LOINC | Non-lab concepts (ECG, cardiac echo, obstetric ultrasound), clinical document types, standardized survey instruments |
Key Elements
Each LOINC term is identified by a unique code in the format nnnnn-n and described by a formal six-part naming convention:
| Axis | Description | Example |
|---|---|---|
| Component | What is measured or observed | Urea, Glucose |
| Property | Characteristic measured | Mass concentration, length |
| Time Aspect | Interval of measurement | Point in time, 24 hours |
| System | Specimen or context | Blood, Urine, Serum |
| Scale | Type of measurement scale | Quantitative, Ordinal, Nominal |
| Method | Procedure used | Enzymatic, Immunoassay |
Serializations & Technical Formats
LOINC is distributed as downloadable database files (CSV and other tabular formats) and is accessible through a FHIR-based terminology service. The Regenstrief LOINC Mapping Assistant (RELMA) desktop application assists with searching and mapping local codes to LOINC codes, with support for English, Spanish, Simplified Chinese, and Korean.
Governance & Maintenance
LOINC is developed and maintained by the Regenstrief Institute and is publicly available at no cost, though users must agree to a license. The standard is updated regularly with new terms and corrections. Harmonization efforts between LOINC and SNOMED CT were initiated in 2012 to ensure complementary use of both terminologies.
Notable Implementations
LOINC is designated as a required standard for U.S. federal government systems for electronic exchange of clinical health information. It was identified by the HL7 Standards Development Organization in 1999 as a preferred code set for laboratory test names. The standard is endorsed by the American Clinical Laboratory Association and is used internationally, with translations and implementations across multiple countries and languages.
Related Standards
- HL7 — Uses LOINC as a preferred code set for laboratory transactions
- SNOMED CT — Complementary clinical terminology; harmonization since 2012
- ICD — International Classification of Diseases, used alongside LOINC in health IT
- DICOM — Digital imaging standard that references LOINC codes