In general population settings, diagnosis of CKD, identification of risk and treatment allocation may be improved by additionally testing serum cystatin C. Cystatin C is a low-molecular-weight protein produced by all nucleated cells and its non-GFR determinants (such as smoking, adiposity, inflammation and glucocorticoid treatment [5]) differ from those of creatinine [6–8]. This evidence concerns the gene CST3 and chronic kidney disease.