Reduced glomerular function and prevalence of gout: NHANES 2009-10

Abstract

Background: The renal tubule is a major route of clearance of uric acid, a product of purine metabolism. The links between reduced glomerular filtration rate (GFR), hyperuricemia, and gout in the general population are not well understood. The objective of the present study was to estimate prevalence of gout and hyperuricemia among people with impaired GFR in the US general population.

Study design: Cross-sectional, survey-weighted analyses of data on adults (age>20 years) in the 2009-10 cycle of the US National Health and Nutrition Examination Surveys (n = 5,589). Associations between self-reported physician diagnosis of gout and degrees of renal impairment were the primary focus of the present analyses.

Results: In the 2009-2010 period, there was an estimated 7.5 million people with gout in the US. There were 1.25 million men and 0.78 million women with moderate or severe renal impairment and gout. The age standardized prevalence of gout was 2.9% among those with normal GFR compared to 24% among those with GFR<60 ml/min/1.73 m(2).In multivariable logistic regression analyses that adjusted for age, gender, body mass index, hypertension, diabetes, hypertension medications, including diuretics, blood lead levels, and hyperlipidemia, the odds ratios of gout and hyperuricemia were 5.9 (2.2, 15.7) and 9.58 (4.3, 22.0) respectively among those with severe renal impairment compared to those with no renal impairment. Approximately 2-3 fold increase in prevalence of gout was observed for each 30 ml/min/1.73 m(2) decrease in GFR, after accounting for the above factors.

Conclusions: Renal glomerular function is an important risk factor for gout. The prevalence of hyperuricemia and gout increases with decreasing glomerular function independent of other factors. This association is non-linear and an eGFR of 60 ml/min/1.73 m(2) appears to be a threshold for the dramatic increase in the prevalence of gout.

Figure 1. Age-standardized prevalence rates of gout and hyperuricemia.

Gout was defined as self-reported physician/provider diagnosis. Hyperuricemia was defined as serum urate >7.0 mg/dL for men and >6 mg/dL for women. Trend tests performed by survey weighted logistic regressions where age and estimated glomerular filtration rates were utilized as continuous measures were statistically significant in both the cases (p<0.001). Conversion factors for units: serum urate in mg/dL to µmole/L, × 59.48.

Figure 2. Bivariate association between estimated glomerular filtration rate and serum urate concentrations.

The curves based on mean serum urate concentration vs. eGFR were fitted by locally weighted scatterplot smoothing (lowess) regressions using unweighted data. Conversion factors for units: serum urate in mg/dL to µmole/L, × 59.48.