[Clinical Importance of GFR-Estimating Equations (eGFRcreat and eGFRcys)]

Evaluation of the renal function is fundamental for the diagnosis and treatment of kidney diseases. It is also important for adjustment of the doses of drugs that are excreted by the kidney. The incidence of contrast-induced nephropathy is high in subjects with a low GFR. Assessment of the renal function is required prior to contrast medium injections. Renal inulin clearance with continuous venous injection is the gold standard for measuring GFR. However, the method is time-consuming. The recent Japanese CKD guide and KDIGO guidelines for CKD management recommended the use of the estimated GFR based on serum creatinine (eGFRcreat) or serum cystatin C (eGFRcys). Because the serum creatinine level is affected by the muscle mass, eGFRcreat is under- or overestimated in subjects with a high or low muscle mass, respectively. The serum cystatin C concentration is less influenced by the muscle mass. Assessment of the renal function by eGFRcys may be useful in subjects with a low or high muscle mass. Recently, it was reported that the association between eGFRcys and the risk of all-cause mortality was much closer compared with eGFRcreat. eGFRcys may be useful for detecting a high risk of complications in a general population and in subjects with CKD.