Evaluation of the albumin cobalt binding (ACB) assay for measurement of ischaemia-modified albumin (IMA) on the Beckman Coulter LX-20.

Background: In the presence of ischaemia, albumin undergoes changes resulting in the formation of ischaemia-modified albumin (IMA). Increased serum concentrations of IMA have been found in patients with myocardial ischaemia. The purpose of this study was threefold: to evaluate the albumin cobalt binding (ACB) assay for measurement of IMA on the Beckman Coulter LX-20; to establish a reference range for IMA; and to investigate the relationship between IMA and total albumin concentrations.

Methods: The ACB assay was evaluated under the following headings: imprecision, accuracy and reliability. A reference range was established on a population of 81 healthy subjects.

Results: The within-batch coefficient of variation (CV) at IMA concentrations of 88, 99 and 120 KU/L were 1.4, 2.0 and 2.5%, respectively. The between-batch CVs at 74, 84 and 123 KU/L were 3.4, 3.3 and 3.0%, respectively. Comparison with the Cobas Mira Plus showed a mean negative bias of 7 KU/L. The 97.5th percentile established on our reference population was 110 KU/L. A significant inverse relationship was found between total serum albumin and IMA concentrations (r = -0.66, P < 0.0001). Correcting the IMA concentrations for total albumin in our reference population, using a formula devised in this study, yielded a range similar to that of uncorrected IMA.

Conclusions: The ACB assay was found to have acceptable precision and performed very satisfactorily on the Beckman Coulter LX-20. A correction to measured IMA concentrations, to take into account total albumin concentrations, may need to be applied for the proper interpretation of IMA results.