Glycated Albumin in Pristine and Non-Pristine Stored Samples in the National Health and Nutrition Examination Survey (NHANES) 1999-2004.

Abstract

Glycated albumin is cleared by the Food and Drug Administration (FDA) for clinical use in diabetes care. To understand its performance in the general US population, we conducted measurements in >19 000 samples from the National Health and Nutrition Examination Survey (NHANES). Of these samples, 5.7% had previously undergone at least 2 freeze-thaw cycles and were considered "non-pristine." We measured glycated albumin and albumin using the Lucica GA-L (Asahi Kasei) assay in stored serum samples from NHANES 1999-2004. Serum albumin (Roche/Beckman) was previously measured. We examined the correlations of percent glycated albumin with hemoglobin A1C (HbA1c)and fasting glucose in the pristine and non-pristine samples. We also measured cystatin C (Siemens) and compared these to cystatin C (Dade Behring) previously obtained in a subsample. Glycated albumin (%) was significantly lower in pristine vs non-pristine samples (13.8% vs 23.4%, P < 0.0001). The results from the Asahi Kasei albumin assay (g/dL) were highly correlated with albumin originally measured in NHANES (Pearson's correlation coefficient, r = 0.76) but values were systematically higher (+0.25 g/dL, P < 0.0001). Cystatin C (Siemens) was similar to previous cystatin C measurements (r = 0.98) and did not differ by pristine status (P = 0.119). Glycated albumin (%) was highly correlated with HbA1c and fasting glucose in pristine samples (r = 0.78 and r = 0.71, respectively) but not in non-pristine samples (r = 0.11 and r = 0.12, respectively). The performance of the glycated albumin assay in the pristine samples was excellent. Performance in non-pristine samples was highly problematic. Analyses of glycated albumin in NHANES 1999-2004 should be limited to pristine samples only. These results have major implications for the use of these public data.