PRECISION OF THE MAGNESIUM DETERMINATION IN MONONUCLEAR BLOOD-CELLS AND ERYTHROCYTES

Objective: Establishing the analytical variation and reproducibility o f the intracellular magnesium (Mg) assay in mononuclear blood cells (M BC) and erythrocytes (RBC). Design and Methods: We assessed the analyt ical variation of the several determination steps, and the reproducibi lity for the complete intracellular Mg-assay (combination of preanalyt ical, analytical, and biological variation). The influence of platelet s was determined by comparing Mg concentrations obtained from heparini zed blood and defibrinated blood. Results: Coefficients of variation o f the several determination steps used in the MBC- and RBC-assay were less than or equal to 5.4%. The overall analytical variation was 5.0-6 .8%, and reproducibility of the complete Mg-assay 11.6-14.0%. Mg measu rements in MBC (expressed as fmol/cell) obtained from heparinized bloo d showed significantly higher values than those obtained from defibrin ated blood. Conclusion: This is the first study to describe in detail reproducibility data for the individual steps in the overall procedure to measure intracellular magnesium. It is shown that results obtained in daily practice should be interpreted with care. Moreover, the remo val of platelets is essential in the determination of Mg in MBC.