Mapping to LOINC
This Implementation Guide is designed with the idea of using pre-harmonized LOINC-coded tests to identify certain kinds of laboratory test types. Pre-harmonized coding is an approach being championed by the SHIELD (Systemic Harmonization and Interoperability Enhancement for Laboratory Data) public-private partnership, and includes a process where the identification of which LOINC term to use for a particular test is vetted through a sole authoritative source. Such an approach helps ensure that the same diagnostic test is coded consistently throughout the health ecosystem.
Best Practices for Mapping to LOINC
Guides for using LOINC Terms
One component of the FDA and other SHIELD stakeholder's work is to develop LOINC coding guides to help laboratories, in vitro diagnostic testing companies, and others apply consistent approaches to identifying the proper LOINC term for a diagnostic test.
A series of these guides are under development by the Regenstrief Institute through a rigorous process that involves pilot testing and multiple rounds of community review by experts. When finalized, these guides represent the best practices for locating the appropriate LOINC term for a given laboratory test.
Presently, a Guide for Using LOINC Microbiology Terms has been published, and a Guide for Using LOINC Allergy Terms and a Quick Start Guide for Mapping to Laboratory LOINC are in draft. Guides for Using LOINC Chemistry Terms and Using LOINC Drug and Toxicology Terms are also under development, but are not available at this time.
We used the available drafts of the these guides to review and modify the Synthea modules and to develop our quality review process.
Although the laboratory test types included in our pilot are not yet covered by published guides, we believe that when available, these guides will be "must reads" for anyone linking local test codes to LOINC terms.
LOINC to Vendor IVD (LIVD) Specification
Another key component of the FDA and other SHIELD stakeholder's approach is the development of the LIVD specification. The LIVD specification is an industry-defined format to publish and exchange the appropriate LOINC terms for vendor IVD test results.
When IVD vendors follow best practices for mapping to LOINC and distribute those mappings in one of the precise and easy to consume LIVD format, laboratories should be able to more consistently, correctly, and efficiently map their tests to LOINC, for the benefit of all downstream recipients of those data.
LIVD specifications can be made available in either a spreadsheet (Microsoft Excel) format or a more computable JSON format. As of the March 18, 2021 publication of LIVD V2.0, the original IICC-developed JSON definition has been replaced by the HL7 FHIR LIVD definition.
SHIELD is actively advancing work towards having an authoritative source for IVD vendor mappings to LOINC. Presently, this effort has primarily been applied to the coding for reporting SARS-CoV-2 test results. A multi-stakeholder team has worked tirelessly to keep an up to date LIVD publication of all SARS-CoV-2 tests listed on FDA Emergency Use Authorizations.
This implementation guide and our pilot incorporates and leverages this authoritative mapping reference for all of the SARS-CoV-2 tests. Because the SARS-CoV-2 LIVD file is published by CDC only in Excel format and is updated frequently, we have not included a copy in this implementation guide, but rather refer users to the CDC site.
We look forward to the more widespread availability of authoritatively curated and centrally available LIVD publications of other laboratory tests.
LOINC Mappings from Reference Laboratories
Within the U.S., nearly all large reference laboratories have comprehensively mapped their laboratory test results to LOINC terms. Most publish those mappings in their online test catalog (or make them available by other means). For example, our pilot clinical site sends some tests to AURP Laboratories, who have been systematically assigning LOINC terms to its assays and makes the mappings available in a spreadsheet for download.
For tests performed by referral laboratories (whether sent out as referral tests or performed directly), the laboratory's published LOINC mappings serve as excellent reference and should enable more efficient and accurate coding of those test results.