Third, as more than two measurements of serum creatinine and cystatin C were available for only 17,841 patients, and those measurements were taken more than 2 years apart, we relied on a single eGFR calculated using the baseline serum creatinine and cystatin C measurements for CKD diagnosis, rather than continuous measurements, which might have resulted in misclassification bias. This evidence concerns the gene CST3 and chronic kidney disease.