National Health and Nutrition Examination Survey

Cystatin C, β-trace protein (BTP) and β2 microglobulin (B2M) assayed from stored surplus serum samples from the NHANES III Second Examination (1988-1994).

Cystatin C, BTP, and B2M were measured in a subsample of stored surplus serum samples obtained from NHANES III Second Examination participants aged 12 years or older who had previous measurements of cystatin C conducted in First Examination NHANES III samples.

Cystatin C, BTP and B2M were measured in 2009 at the University of Minnesota (1, 2). Cystatin C measurements were conducted using the Siemens (formerly Dade Behring) N Latex Cystatin C assay, an automated particle-enhanced nepholometric assay (Siemens Diagnostics). BTP was assayed using the N Latex β-trace protein assay (Siemens Diagnostics). B2M was assayed using the N Latex β2 microglobulin assay (Siemens Diagnostics).

All data have been made publicly available.

The inter-assay coefficients of variation for the cystatin C, βTP and β2M assays were 4.0% (mean 0.698 mg/L), 5.7% (mean 0.594 mg/L) and 2.7% (mean 1.757 mg/L), respectively.

The Second Examination of NHANES III is a convenience sample of the larger NHANES III population and no sample weights are applied to this subsample. Cystatin C calibration has varied substantially across laboratories between 2006—when the original NHANES III (First Examination) cystatin C stored surplus sera study was conducted —and 2009—when the present measurements were conducted. Due to differences in laboratory calibration of assays, there are systematic differences in the cystatin C values from the First Examination and those from the Second Examination and other NHANES surveys. Users need to consider the shift in laboratories when comparing cystatin C measurements from the Second Examination samples to measurements from the First Examination and other NHANES samples, conducted at different time points.