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Is repeat serum urate testing superior to a single test to predict incident gout over time?

ABSTRACT: Elevated serum urate is the most important causal risk factor for developing gout. However, in longitudinal cohort studies, a small proportion of people with normal urate levels develop gout and the majority of those with high urate levels do not. These observations may be due to subsequent variations in serum urate over time. Our analysis examined whether single or repeat testing of serum urate more accurately predicts incident gout over time. Individual participant data from three publicly-available cohorts were included. Data from paired serum urate measures 3–5 years apart, followed by an assessment of gout incidence 5–6 years from the second urate measure were used to calculate the predictive ability of four measures of serum urate on incident gout: the first measure, the second measure, the average of the two measures, and the highest of the two measures. Participants with prevalent gout prior to the second measure were excluded. Receiver operator characteristic (ROC) curves and area under the curve (AUC) statistics were computed to compare the four measures. A total of 16,017 participants were included across the three cohorts, with a mean follow-up from the first serum urate test of 9.3 years (range 8.9–10.1 years). Overall, there was a small increase in the mean serum urate between the first and second measures (322 μmol/L (5.42 mg/dL) vs. 340 μmol/L (5.71 mg/dL), P<0.001) which were a mean of 3.5 years apart, but the first and second measures were highly correlated (r = 0.81, P<0.001). No differences were observed in the predictive ability of incident gout between the four measures of serum urate measurement with ROC curve AUC statistics ranging between 0.81 (95% confidence intervals: 0.78–0.84) and 0.84 (95% confidence intervals: 0.81–0.87). These data show that repeat serum urate testing is not superior to a single measure of serum urate for prediction of incident gout over approximately one decade.

SUBMITTER: Stewart S

PROVIDER: S-EPMC8806054 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundPrevious studies have noted significant variation in serum urate (sUA) levels, and it is unknown how this influences the accuracy of hyperuricemia classification based on single data points. Despite this known variability, hyperuricemic patients are often used as a control group in gout studies. Our objective was to determine the accuracy of hyperuricemia classifications based on single data points versus multiple data points given the degree of variability observed with serial measurements of sUA.MethodsData was analyzed from a cross-over clinical trial of urate-lowering therapy in young adults without a gout diagnosis. In the control phase, sUA levels used for this analysis were collected at 2-4 week intervals. Mean coefficient of variation for sUA was determined, as were rates of conversion between normouricemia (sUA ≤6.8 mg/dL) and hyperuricemia (sUA > 6.8 mg/dL).ResultsMean study participant (n = 85) age was 27.8 ± 7.0 years, with 39% female participants and 41% African-American participants. Mean sUA coefficient of variation was 8.5% ± 4.9% (1 to 23%). There was no significant difference in variation between men and women, or between participants initially normouricemic and those who were initially hyperuricemic. Among those initially normouricemic (n = 72), 21% converted to hyperuricemia during at least one subsequent measurement. The subgroup with initial sUA < 6.0 (n = 54) was much less likely to have future values in the range of hyperuricemia compared to the group with screening sUA values between 6.0-6.8 (n = 18) (7% vs 39%, p = 0.0037). Of the participants initially hyperuricemic (n = 13), 46% were later normouricemic during at least one measurement.ConclusionSingle sUA measurements were unreliable in hyperuricemia classification due to spontaneous variation. Knowing this, if a single measurement must be used in classification, it is worth noting that those with an sUA of < 6.0 mg/dL were less likely to demonstrate future hyperuricemic measurements and this could be considered a safer threshold to rule out intermittent hyperuricemia based on a single measurement point.Trial registrationData from parent study ClinicalTrials.gov Identifier: NCT02038179 .

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Is repeat serum urate testing superior to a single test to predict incident gout over time?

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