In adults with CKD stages 3–4, serum creatinine, cystatin C and β2-microglobulin demonstrated high discriminatory performance for separating stage 3 from stage 4 kidney dysfunction when classification was defined using the 2021 CKD-EPI equations, including eGFRcr and eGFRcr–cys. This evidence concerns the gene CST3 and chronic kidney disease.