A 20-Year Evaluation of LOINC in the United States' Largest Integrated Health System.

CONTEXT.—: Clinical laboratories are obligated to implement Logical Observation Identifier Names and Codes (LOINC), an informatics standard used to uniquely identify laboratory tests. The historical progress of laboratories in achieving this goal is unknown. OBJECTIVE.—: To evaluate the implementation of LOINC by clinical laboratories with attention to LOINC's adoption, diversity, and correctness over time. DESIGN.—: We aggregated data from 130 facilities within the Veterans Health Administration (VA), an early adopter of LOINC, during a 20-year period (1999-2018). To assess the adoption of LOINC, we calculated the annual proportion of tests and results without a LOINC. To assess the diversity of LOINC, we counted the yearly number of distinct LOINCs in active use. To assess the correctness of LOINC over time, we compared the assigned LOINCs to a manually reviewed gold standard for each year. RESULTS.—: We reviewed a total of 586 000 tests and 9.162 billion results. LOINC adoption, measured as a proportion of both tests and results, improved over time (P < .001). In the final year reviewed, 85% (172 142 of 202 125) of laboratory tests and 99% (547 229 066 of 551 205 087) of results had LOINCs. The number of distinct LOINCs in active use from 1999 to 2018 increased 2.78-fold from 4502 to 12 503 (P < .001). Correctness generally improved but varied considerably by test and across time. CONCLUSIONS.—: The adoption of LOINC has improved during the past 2 decades. More diverse LOINCs were associated with increased adoption and were a challenge to keep up-to-date. The correctness of LOINCs has improved but remains an issue that likely necessitates supplemental review for most applications.