These formulae use serum creatinine concentrations, as advocated for screening [7]; however, additional CKD-EPI equations include cystatin C. Cystatin C has been evaluated as an alternative filtration marker to serum creatinine and has been reported to be a better marker than creatinine [12]; estimated GFR (eGFR) based on cystatin C equations may be used as a confirmatory test for renal disease [13]. The gene discussed is CST3; the disease is chronic kidney disease.