Quantitative Turbidimetric Assay for Determining Myoglobin Evaluated

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Abstract
A recently introduced turbidimetric immunoassay using shell/core particles for determination of myoglobin (Turbiquant Myoglobin, Behringwerke, Marburg, Germany) was evaluated on the Behring Turbitimer analyzer. Intra-assay CV varied between 1 · 0% and 3 · 2%; interassay CV was between 2 · 0% and 3 · 6%. Linear results were obtained between 2 · 8 nmol/L and 36 · 7 nmol/L. Manual dilution in saline solution allowed measurement of myoglobin concentrations up to 25 400 nmol/L. In the tested range, no high-dose ‘hook’ effect was observed. Haemolysis interfered with the assay when haemoglobin concentrations exceeded 2 g/L. The occurrence of error codes due to the presence of triglycerides was shown to depend on particle size. Repeat assays on diluted samples were necessary at triglyceride concentrations of 2 · 3 mmol/L for post-prandial chylomicrons (200–1000 nm), and at 11–31 mmol/L for very-low density lipoprotein-triglycerides (80–200 nm). No significant interferences of haptoglobin, bilirubin, iodine containing contrast media, and rheumatoid factors were detected for the assay. Treatment of lipaemic samples with Lipoclean (Behringwerke) resulted in lower myoglobin values. Simultaneously drawn serum and heparin-plasma samples gave comparable myoglobin results. However, values obtained in EDTA- or citrate-treated plasma samples occasionally differed significantly from serum values. The upper reference limit for myoglobin concentration was 4 · 2 nmol/L. The turbidimetric assay correlated well with a radioimmunoassay (Byk-Sangtec; r = 0 · 892) and with the automated nephelometric assay (Behringwerke; r = 0 · 944). Values obtained by turbidimetry were comparable to those obtained by the latex agglutination test (Behringwerke).