Supplementary Material for: Threshold Effects of Serum Uric Acid on Chronic Kidney Disease in US Women without Hypertension and Diabetes: A Cross-Sectional Study

Background: Serum uric acid (SUA) has been associated with increased risk of chronic kidney disease (CKD) in observational studies; however, data in women without hypertension and diabetes are sparse. Purpose: To examine the association between SUA and CKD among women without hypertension and diabetes. Methods: In this cross-sectional study of 6,776 US women without hypertension and diabetes from the National Health and Nutrition Examination Survey (1999–2006), we investigated the relationship between SUA and CKD using multivariable logistic regression models. Moreover, a generalized additive model and smooth curve fitting (penalized spline method) and a 2 piecewise logistic regression models were conducted to address for nonlinearity. Results: The prevalence of CKD was 8.3%. Multiple logistic analyses showed that per 1 mg/dL increase in SUA was associated with 39% increased prevalence of CKD. Analyses using restricted cubic spline confirmed that the association between SUA and CKD was nonlinear. Further, threshold and saturation effect analysis showed that the inflection point of SUA was 4.5 mg/dL. The ORs (95% CIs) were 0.84 (0.66–1.08) on the left side of inflection point and 1.87 (1.56–2.24) on the right side of inflection point, respectively. Subgroup analysis showed that the stronger association between SUA and CKD was observed in elder women with never/former smoking and higher fasting blood glucose levels (all p values for interaction <0.05). Conclusion: Our study suggested threshold effects of SUA on the prevalence of CKD among US women without hypertension and diabetes. SUA levels >4.5 mg/dL were positively and independently associated with CKD.