Measurement of Serum Albumin by Capillary Zone Electrophoresis, Bromocresol Green, Bromocresol Purple, and Immunoassay Methods

Background/aims: The introduction of capillary zone electrophoresis (CZE) to this laboratory has highlighted discrepancies in albumin measured on an Abbott Aeroset by bromocresol green (BCG) and that calculated by CZE on the basis of total protein measured by Biuret.

Methods: This study examined differences in albumin estimation by CZE, Abbott Aeroset BCG, and Aeroset bromocresol purple (BCP), and compared these with albumin estimated by Beckman Array immunoassay.

Results: Altman and Bland analysis of results showed a positive bias of BCG with CZE (4.51 g/litre; 95% limits of agreement, 3.77 to 5.26; n = 72) and BCP (3.85 g/litre; 95% limits of agreement, -1.42 to 9.12; n = 72). CZE and BCP agreed closely (0.67 g/litre; 95% limits of agreement, -4.39 to 3.06; n = 72). Analysis of 57 of those samples in which BCG and CZE differed > or = 5 g/litre showed a positive bias of BCG with immunoassay (8.35 g/litre; 95% limits of agreement, 1.54 to 15.16; n =57), with good agreement between CZE and immunoassay (-0.44 g/litre; 95% limits of agreement, -2.82 to 1.94; n = 57).

Conclusions: BCP is superior to BCG for the assay of albumin and has replaced BCG as the routine test for albumin in this laboratory.