Multicenter evaluation of five assays for myoglobin determination

Background: Lacking assay standardization, different myoglobin methods may produce results that differ significantly. Methods: A multicenter study was carried out to compare the analytical performance of five commercially available assays for myoglobin measurement. Linearity, imprecision, interferences, and method comparison were studied according to NCCLS guidelines, whereas reference values were determined following IFCC recommendations; Results: The BNA and Opus showed relatively high imprecision (all but one total CV >7.4%). Other assays showed lower CVs, but they varied among laboratories, particularly at a normal myoglobin concentration (Access, 6.0-11%; Hitachi, 3.8-5.8%; Stratus, 3.4-6.5%). Results were lower in anticoagulated samples on the Access, in heparin and citrate samples on the Stratus, and in citrate samples on the BNA and Opus, and increased in heparin and EDTA samples on the Hitachi. Use of separator gel produced results significantly lower (P <0.001) on the Hitachi and higher (P = 0.016) on the Opus. Bilirubin, turbidity, and hemoglobin had no effect on evaluated methods, but rheumatoid factor affected the Access. In method comparisons, high correlation coefficients (greater than or equal to 0.98) were obtained. The Stratus gave higher results; however, the Access and BNA gave the lowest. The following upper reference limits (mu g/L) for men and women, respectively, were obtained: Access, 70 and 52; BNA, 51 and 49; Hitachi, 67 and 58; Opus, 80 and 50; and Stratus, 86 and 63. Conclusion: The possibility of high imprecision and marked disagreement among commercial myoglobin assays should be carefully considered in clinical practice.