“…But this is very likely due to the non-GFR determinants of cystatin C being predictive of morbidity and mortality rather than just improved estimation of GFR by cystatin C. First, an elevated cystatin C level is just as predictive of mortality in persons without CKD (in whom GFR variation is physiologic) as it is in persons with CKD (in whom GFR variation is pathologic) (6). Second, hyperfiltration by mGFR or urinary creatinine clearance is associated with CKD risk factors and complications (obesity, diabetes, hypertension, left ventricular hypertrophy) (20)(21)(22)(23)(24), with developing albuminuria (25)(26)(27)(28), with structural abnormalities in the kidney (cysts, enlarged kidneys, and decreased glomerular density) (29)(30)(31)(32)(33), and with subsequent GFR decline and ESRD (29,34,35). Although eGFR Cr also identifies hyperfiltration as an increasedrisk state (16,24,28,35,36), eGFR Cys identifies hyperfiltration as a low-risk state (Figure 3) (16,23,24,35).…”