Cystatin C levels in U.S. adults, 1988-1994 versus 1999-2002: NHANES.

BACKGROUND AND OBJECTIVES Creatinine-based estimates of GFR suggest an evolving epidemic of chronic kidney disease (CKD) in U.S. adults that is inadequately explained by conventional, modifiable risk factors. Cystatin C has recently emerged as a promising measure of GFR. To enable further insights into the evolution of CKD in the U.S. population, this study aimed to examine cystatin C levels in U.S. adults. DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS Stored serum samples, measured in 2006, were used to compare cystatin C levels among adult participants in the National Health and Nutrition Examination Survey (NHANES) in two time periods, 1988-1994 (n = 6877) and 1999-2002 (n = 4563). RESULTS Mean cystatin C levels (0.9 versus 0.9 mg/L, P = 0.65) and urinary albumin-creatinine ratios were similar (5.8 versus 5.9 mg/g, P = 0.19) in the 2 study eras. In contrast, standardized serum creatinine (0.8 versus 0.9 mg/dl, P < 0.0001) was higher and estimated GFR (93.2 versus 87.6 ml/min/1.73 m(2), P < 0.001) was lower in 1999-2002. Similar discrepancies in population trends (when cystatin C and creatinine-based methods were used to define GFR) were present when categories of kidney function were considered, and when adjustment was made for demography and comorbid illness. CONCLUSIONS The disparity between temporal trends when kidney function is assessed with different measurements suggests that estimating trends in disease burden remains an open question.