Preparation of highly purified monomeric human serum albumin as secondary reference material for standardization of urinary albumin immunoassays

Background: International external quality assessments have shown variation in results of urinary albumin among various immunoassays. A well-defined candidate reference material for urine albumin (cRM-UA) was prepared to improve standardization. Methods: cRM-UA was prepared from a commercially available preparation of human serum albumin by using gel-filtration HPLC. The value was assigned by transfer from ERM-DA470 using immunoassay systems qualified based on the linearity and variability observed in dilution tests of pooled urine and the calibrators. Effectiveness of recalibration using the cRM-UA was evaluated by measuring 129 urine specimens. Results: The cRM-UA had a monomeric albumin peak which accounted for 98.9% of the total area by gel filtration HPLC. The lyophilized preparation of the cRM-UA had suitable homogeneity, and short- and long-term stability. Nine of 14 immunoassays met the criteria were used for value assignment. The assigned concentration was 225.1 +/- 9.11 mg/l [mean +/- U: expanded uncertainty with k = 2] when reconstituted with 3.00 ml of purified water on weight basis. Recalibration of 7 qualified immunoassays using the cRM-UA resulted in between-method CV of 6.6%. Conclusions: The cRM-UA was successful in achieving standardization of urine albumin results among 7 immunoassays which possess performance attributes representing uniform reactivity to both cRM-UA and clinical urine samples. (C) 2011 Elsevier B.V. All rights reserved.