Background/Purpose: Elevated serum uric acid (UA) concentration is associated with the urate crystal deposition disorders gout and nephrolithiasis, as well as hypertension, the metabolic syndrome, chronic kidney disease, and cardiovascular disease. Hyperuricemia is often defined as a serum urate level greater than 6.8 – 7.0 mg/dL, a physicochemical cutoff above which monosodium urate crystals precipitate in body fluids. Here, we determined whether leading United States (U.S.) hospitals used this physicochemical cutoff in their definition of the reference ranges for serum UA, and if the reference ranges were consistent across institutions.

Methods: The top 20 hospitals listed in the U.S. News & World Report Best Hospitals 2018-2019 rankings were queried. Data were obtained in May 2019 using either online publicly available information, or by telephone contact with the laboratory. Information about the type of assay used to measure serum uric acid was obtained. Reference ranges reported by each laboratory for adult males and females were obtained. If a given laboratory reported age-dependent reference ranges for a given sex, the median UA thresholds for that sex were used.

Results: All surveyed laboratories reported utilizing enzymatic (uricase) methods, which were obtained from a variety of instrument manufacturers. The median reported upper limit of the reference range (ULRR) for UA in males was 8.0 mg/dL (range 7.0 – 9.0 mg/dL). The median reported ULRR for females was 6.6 mg/dL (range 5.7 – 8.0 mg/dL). Among the 20 laboratories, 12 different upper limits were used for males, and 11 different upper limits were used for females. For adult males, 15% of hospitals reported an ULRR of 6.8 – 7.0, while 85% used an ULRR greater than 7.0, and 0% used an ULRR less than 6.8. For adult females, 15% of hospitals used an ULRR of 6.8 – 7.0, 30% used an ULRR greater than 7.0, and 55% used an ULRR less than 6.8. Only one laboratory used an age-adjusted reference range.

Conclusion: The upper limits of the reference ranges for serum UA reported by leading U.S. hospitals do not consistently align with the physicochemical definition of hyperuricemia. Additionally, there is considerable variability in the ULRR among surveyed hospitals. This likely reflects use of population-based distributions rather than physicochemical criteria to define hyperuricemia. Most surveyed hospitals used an ULRR for adult females which was lower than 6.8. Most hospitals surveyed used an ULRR for adult males which was higher than 7.0. This practice may result in under-recognition of clinically significant hyperuricemia and under-dosing of uric acid lowering agents in the treatment of gout in male patients.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/inconsistency-in-uric-acid-reference-ranges-among-20-top-united-states-hospitals-what-is-normal/