Serum cystatin C in the United States: the Third National Health and Nutrition Examination Survey (NHANES III).

<bold>Background: </bold>Serum cystatin C increasingly is used as a marker of glomerular filtration rate and cardiovascular risk. However, information for serum cystatin C levels in the general population, specifically across a wide age range and different ethnicities, is lacking.<bold>Objectives: </bold>To determine nationally representative serum cystatin C levels, estimate the prevalence of increased cystatin C levels in the general population, and identify factors associated with increased cystatin C levels.<bold>Study Design: </bold>Cross-sectional survey.<bold>Setting and Participants: </bold>A nationally representative subsample of 7,596 participants aged 12 years or older in the Third National Health and Nutrition Examination Survey conducted in 1988-1994.<bold>Predictors: </bold>Age, sex, race/ethnicity, risk factors for chronic kidney disease.<bold>Outcomes: </bold>Continuous serum cystatin C levels and serum cystatin C level greater than 1.12 mg/L.<bold>Measurements: </bold>Cystatin C was measured in 2006 from stored sera by using an automated particle-enhanced nephelometric assay.<bold>Results: </bold>Overall median serum cystatin C level was 0.85 mg/L. Median cystatin C levels increased steeply with age and were greater in males and non-Hispanic white persons, even in a healthy subgroup of 20- to 39-year-olds. Prevalences of increased serum cystatin C levels (>1.12 mg/L) were 1%, 41%, and greater than 50% in all persons aged younger than 20 years, 60 years or older, and 80 years or older. In persons aged 60 years and older, older age, non-Hispanic white ethnicity, hypertension, current smoking, lower levels of education and high-density lipoprotein cholesterol, and increased body mass index, C-reactive protein, and triglyceride values were associated significantly with increased serum cystatin C levels.<bold>Limitations: </bold>No measured glomerular filtration rate, single measurement of cystatin C, cross-sectional study design.<bold>Conclusions: </bold>Serum cystatin C level is related to sex and ethnicity, even in young healthy individuals. The prevalence of increased cystatin C levels increases dramatically with age, reaching greater than 50% after the age of 80 years in both sexes and all ethnic groups. [ABSTRACT FROM AUTHOR]