1 Introduction

LOINC provides a set of universal names and ID codes for identifying laboratory⁴ and clinical test results⁵. LOINC facilitates the exchange and pooling of results, such as blood hemoglobin, serum potassium, or vital signs, for clinical care, outcomes management, and research. LOINC’s universal identifiers (names and codes) can be used in the context of order and observation exchanges between information systems that use syntax standards such as HL7⁶, CEN TC251, ISO TC215, ASTM⁷, and DICOM. Specifically, the identifier can be used as the coded value for an observation in any other standard that uses the observation/observation value paradigm, whether messages, documents, application programming interface (API), etc. For example, LOINC codes are used widely in the OBX segment “Observation Identifier” field (OBX-3) of an ORU HL7 (HL7 version 2.x or ASTM 1238-9410) message that may be sent between a Clinical Laboratory Information Management Systems⁸ (LIMS) and Electronic Health Record Systems⁹ (EHR). In this way, LOINC codes provide “universal” identifiers that allow the exchange of clinical data between heterogeneous computing environments.

If data producers use only their internal (and idiosyncratic) codes to identify the variables, then receiving medical information systems cannot fully “understand” the results they receive unless they either adopt the producer’s codes (which is impossible if information system receives results from multiple sources, or invest in the work to map each producer’s coding system to their internal code system¹⁰. If medical information producers who wish to communicate with each other adopt LOINC codes to identify their results in data transmissions, this problem would disappear. The receiving system with LOINC codes in its master vocabulary file would be able to understand and properly file HL7 results messages that identified clinical observations via LOINC codes. Similarly, if test and observation codes were reported with the LOINC codes, government agencies would be able to pool results for tests from many sites for research management and public health purpose. LOINC terms should be of interest to many in the healthcare ecosystem, including hospitals, clinical laboratories, outpatient services, state health departments, governmental health care providers, health IT vendors, diagnostic testing vendors, third-party payers, and organizations responsible for quality assurance and utilization review.

In the beginning, we used many sources as substrate that informed the creation of LOINC, including the Silver Book from the International Union of Pure and Applied Chemistry (IUPAC) and the International Federation of Clinical Chemistry¹¹ (IFCC), textbooks of clinical pathology (e.g., Henry¹² and Tietz¹³), the expertise and work of the LOINC members, and EUCLIDES. We also reviewed the master test files of eight sources (Indiana University/Regenstrief, University of Utah, Association of Regional and University Pathologists (ARUP), Mayo Medical Laboratories, LDS Hospital in Salt Lake City, the Department of Veterans Affairs, Quest Diagnostics, and University of Washington). From the start, this was an empirical effort with the goal to provide codes that correspond to the concepts in real world laboratories’ and clinical departments’ master files.

We aim to achieve a level of detail in the definition of a LOINC term that will map one-to-one to the separately reported observations on a clinical laboratory or other clinical system report. If a test has its own column on a clinical report, or has a reference range that is significantly different from other tests, or has a different clinical meaning than other related tests, it will usually be assigned a separate LOINC code and name. LOINC creates terms both for individual variables (reportable tests or clinical measurements) and collections of such variables. We create terms that represent two kinds of collections: Panels, where the child elements are enumerated, and Documents where the terms represent general information collections whose contents are not explicitly enumerated.

The Regenstrief Institute maintains LOINC and makes it available in a number of formats. LOINC and the related files (such as this document) are copyrighted to assure that multiple variants of the standard do not emerge. Having many variants would defeat the purpose of a universal identifier for test results. LOINC is made available at no cost worldwide under the license at http://loinc.org/license. The LOINC Table, supporting documentation and supplemental files, and the RELMA® mapping program are all made available by the Regenstrief Institute on the LOINC website (http://loinc.org). LOINC content and associated documentation has been translated into many languages in further support of adoption globally¹⁴.

Section Contents