Cystatin C is a cysteine protease inhibitor that is freely filtered by the glomerulus and is therefore a measure of renal function. In this study of elderly persons, the serum cystatin C level was a better predictor of the risk of death and cardiovascular disease than was the serum creatinine level. Cystatin C is a useful alternative measure of renal function, as well as an effective prognostic tool. In this study of elderly persons, the serum cystatin C level was a better predictor of the risk of death and cardiovascular disease than was the serum creatinine level. The presence of renal dysfunction in elderly persons has been associated with an increased risk of death among healthy persons in outpatient care 1 , 2 and among those with several clinical factors, including heart failure, 3 acute hospitalization, 4 inpatient surgery, 5 , 6 and acute myocardial infarction. 7 , 8 However, the primary clinical tool for measuring renal function, the serum creatinine level, is insensitive for the detection of moderate reductions in renal function and is affected by factors unrelated to renal function, such as age, sex, race, and lean muscle mass. Creatinine-based equations to estimate the glomerular filtration rate (GFR) have been derived to compensate . . .