Cystatin C Levels in US 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. Clin J Am Soc Nephrol 4: 965-972, 2009. doi: 10.2215/CJN.05281008