Is High Serum Uric Acid a Risk Marker or a Target for Treatment? Examination of its Independent Effect in a Large Cohort With Low Cardiovascular Risk

Background: Cohort studies evaluating increased uric acid level as a cardiovascular disease (CVD) risk factor have shown variable results; studies are particularly lacking in lower risk populations. Study Design: Prospective cohort study. Setting & Participants: 484,568 adults participating in a medical screening program in Taiwan since 1994 were followed up for a median of 8.5 years. Two subgroups were constructed: the first (n = 246,697; 51%) excluded participants with either overt CVD or overt CVD risk factors (including hypertension, diabetes, obesity, and hypertriglyceridemia) and the second (n = 157,238; 32%) further excluded individuals with early-stage CVD risk factors (including prehypertension, prediabetes, overweight, and borderline hypertriglyceridemia). Predictor: Serum uric acid. Outcomes & Measurements: All-cause and CVD mortality risk assessed using Cox proportional hazards models for categorical and continuous serum uric acid levels. As applicable, models adjusted for 14 variables. Population-attributable fraction was applied to compare contributions to mortality between high uric acid level and other CVD risk factors. Results: In the total cohort, mean age was 41.4 +/- 4.0 years and 26.2% had serum uric acid levels >= 7 mg/dL. Through 2007, there were 16,246 deaths (3.4% of all participants), with 35.2% of deaths occurring in individuals with hyperuricemia. Adjusted HRs associated with serum uric acid levels mg/dL for all-cause and CVD mortality were 1.10 (95% CI, 1.04-1.17) and 1.38 (95% CI, 1.20-1.58), respectively. In individuals with hyperuricemia, 64.3% had overt CVD risk factors and 82.5% had either overt or early-stage CVD risk factors. Individuals with serum uric acid levels >= 8 mg/dL without overt CVD risk factors constituted 13.5% of the total study population with hyperuricemia; in analyses excluding those with overt CVD risk factors, serum uric acid level >= 8 mg/dL was significantly associated with all-cause and CVD mortality, with HRs of 1.37 (95% CI, 1.18-1.60) and 2.30(95% CI, 1.51-3.49), respectively. In the subgroup of those with serum uric acid levels >= 8 mg/dL but who lacked both overt and early-stage CVD risk factors, the HRs for all-cause and CVD mortality were also significant and were 1.39 (95% CI, 1.08-1.78) and 2.38 (95% CI, 1.24-4.54), respectively. HRs for individuals with the same risk profiles but with serum uric acid of 7.0-7.9 mg/dL were not significant. In all groups, inclusion of proteinuria and glomerular filtration rate in models substantially attenuated the association between uric acid level and outcomes. High uric acid levels contributed a relatively insignificant portion to mortality (1.2%) and CVD deaths (4.5%) in this population. Limitations: A single measurement of uric acid was used. Conclusion: Increased serum uric acid level is a minor, but significant, risk factor for all-cause and CVD mortality. However, except for a small proportion (13.5%), increased serum uric acid level is more a risk marker than a target for treatment and is not an independent risk. Determining appropriate groups to target in clinical trials for uric acid lowering therapy is critical. Am J Kidney Dis 56:273-288. (C) 2010 by the National Kidney Foundation, Inc.