Logical Observation Identifiers Names and Codes (LOINC) are self-defining names (source vocabulary) for laboratory and clinical observations included as a reference terminology in the Unified Medical Language System (UMLS). The LOINC database provides a set of universal names and ID codes for identifying laboratory and clinical results in the context of widely adopted existing observation report messaging standards including HL7. LOINC, as a controlled vocabulary standard together with other health information technology standards, is an essential element that enables semantic interoperability through efficient electronic translation processing (exchange) and storage of clinical results coming from many different independent sources (systems) in an understandable way.
LOINC is a voluntary effort housed in the Regenstrief Institute for Health Care, an internationally respected non-profit medical research organization associated with Indiana University. LOINC system was initiated in 1994 by Dr. Clem McDonald, an investigator at the Regenstrief Institute. The LOINC committee was formed by Regenstrief to develop a definitive standard for identifying clinical information (tests and observations) in electronic reports as a response to the growing demand for electronic movement of clinical data to hospitals, physician's offices, and payers who use the data for clinical care and management purposes. Prior to LOINC, many systems were sending procedure and measurement results using institution-specific names and codes which made health data exchanges across systems difficult to do efficiently due to a lack of a standardized structure.
Since its start, LOINC has been an open standard and distributed at no cost worldwide. LOINC has been widely adopted in both the public and private sector, in the U.S. and internationally to share and aggregate health data. Many countries outside of the U.S. have adopted LOINC as a national standard or use in large health information exchange systems. Within the U.S., the HITECH Act and its "meaningful use" criteria for certified EHR technology resulted in the adoption of LOINC as the standard for lab orders and their results. Also, in the U.S., LOINC is used by several major organizations for health data exchange including large reference laboratories, healthcare organizations, software vendors, federal agencies, insurance companies, in vitro diagnostic manufacturers, regional health information networks, and national standard bodies. There are presently over 69,500 registered users from 172 countries. To date, LOINC content and documentation has been translated into 13 languages in 21 countries to meet the needs of different jurisdictions.
LOINC is a universal coding system for identifying laboratory and clinical observations to enable the exchange and accumulation of results for clinical care, research, and outcomes management. The intent of LOINC codes is to identify the test result or clinical observation. LOINC codes represent the “question” for a test or measurement. Where needed, codes from other standards (e.g. SNOMED CT) represent the “answer”. The overall scope of LOINC is anything that one can test, measure, or observe about a patient.
There are two major divisions of the content in LOINC: Laboratory and Clinical. The laboratory portion of LOINC covers anything that can be tested, measured, or observed about a specimen. It contains the usual categories of chemistry, hematology, serology, microbiology, toxicology; and more. The clinical portion of LOINC covers anything that can be tested, measured, or observed about a patient without collecting a specimen from them. LOINC has codes for clinical observations including vital signs, hemodynamics, intake/output, EKG, obstetric ultrasound, cardiac echo, urologic imaging, gastro-endoscopic procedures, pulmonary ventilator management, radiology studies, clinical documents, selected survey assessment instruments (e.g. Glasgow Coma Score, PHQ-9 depression scale, CMS-required patient assessment instruments), and other clinical observations.
LOINC constructs “fully specified” names (FSN) according to an established model that has six main axes (fields) for each term for a laboratory or clinical observation identity. The LOINC database currently has over 87,860 observation terms (Version 2.64 – released June 2018) that can be applied and understood universally. Of note, the first publication of the LOINC database was in 1995 with less than 10,000 terms. Each database record has the following axes (fields):
- Component (analyte) – the substance or entity being measured or observed.
- Property – the characteristic or attribute of the analyte.
- Time (aspect) – the interval of time over which an observation was made.
- System (specimen) – the specimen or thing upon which the observation was made
- Scale (Precision) - how the observation value is quantified or expressed: quantitative, ordinal (ranked choices), nominal (unranked choices) or narrative.
- Method (OPTIONAL axis) – a high-level classification that identifies how the observation was made. It is only needed to distinguish observations when the technique affects the clinical interpretation of the results.
LOINC code 806-0 represents a “manual count of white blood cells in cerebral spinal fluid specimen” and the breakdown by its fields is the following:
- Component = Leukocytes (white blood cells)
- Property = NCnc (number concentration)
- Time = Pt (Point in time)
- System = CSF
- Scale = Qn (Quantitative)
- Method = Manual count
LOINC creates several different text names (labels) to represent each concept. The 6-part formal name described above is the Fully-specified Name (FSN). There are two other more clinician-friendly displays called the Long Common Name (LCN) and a Short Name that can be useful when there is a need for a column header in a report. Using LOINC code 806-0 as an example again, here are its associated names:
- Fully-Specified Name (FSN) = Leukocytes: NCnc: Pt: CSF: Qn: Manual count
- Long Common Name (LCN) = Leukocytes [#/volume] in Cerebral spinal fluid by Manual count
- Short Name = WBC # CSF Manual
LOINC is distributed at no cost from the LOINC website (http://loinc.org ) as a database table (available in several formats) containing the LOINC codes, names, and many additional attributes including synonyms, alternate names, example units, and reference ranges, etc. New versions of the LOINC codes database are published twice yearly – in June and December. In addition, Regenstrief maintains and distributes at no cost a software program called RELMA (the REgenstrief LOINC Mapping Assistant) that helps users map their local terms or lab tests to universal LOINC codes. RELMA contains many tools that will help search for the correct LOINC codes to map to local terms or lab tests.
LOINC can be explored by viewing directly in web browsers at . Updated versions of LOINC and the RELMA desktop Microsoft Windows-based mapping utility program can be accessed at . Between the public releases, a “pre-release” view of new codes that have been requested by users and processed for development by the LOINC team can be viewed at .
- Edward H. Shortliffe and James J. Camino, Biomedical Informatics: Computer Applications in Health Care and Biomedicine, Fourth Edition (New York: Springer 2014) 232-233.
- LOINC.org “About LOINC” ( )
- LOINC.org “LOINC Get Started” ( )
- LOINC.org “LOINC Frequently Asked Questions” ( )
- LOINC – A Universal catalog of individual clinical observations and uniform representation of enumerated collections. Int J Inform Personal Med 2010; 3(4):273-291. 
Submitted by Richard Hammel