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

Abstract 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.