Sarah Stewart, Amanda Phipps-Green, Greg D. Gamble, Lisa K. Stamp, William J. Taylor, Tuhina Neogi, Tony R. Merriman, Nicola Dalbeth
University of Auckland
Background: Elevated serum urate is the most important 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. It is unclear whether repeated testing of serum urate improves the ability to accurately predict development of gout.
Objective: To examine whether single or repeat testing of serum urate more accurately predicts incident gout over time.
Methods: 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 models of serum urate measurement 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 from logistic regression analyses adjusted for age, gender, sex and cohort to compare the four models of urate measurement.
Results: 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. Overall, there was a small increase in the mean serum urate between the first and second measures (5.42 mg/dL vs. 5.71 mg/dL, P < 0.001), but the first and second measures were highly correlated (r = 0.814, P < 0.001). No differences were observed in the predictive ability of incident gout between the four models of serum urate measurement with ROC curve AUC statistics ranging between 0.81 and 0.84.
Conclusion: Repeat serum urate testing is not superior to a single measure of serum urate for prediction of incident gout over approximately one decade. These results may inform the design of longitudinal studies of incident gout, and clinical practice when providing advice to individuals about their risk of developing gout.