Precision of the magnesium determination in mononuclear blood cells and erythrocytes.

OBJECTIVE Establishing the analytical variation and reproducibility of the intracellular magnesium (Mg) assay in mononuclear blood cells (MBC) and erythrocytes (RBC). DESIGN AND METHODS We assessed the analytical variation of the several determination steps, and the reproducibility for the complete intracellular Mg-assay (combination of preanalytical, analytical, and biological variation). The influence of platelets was determined by comparing Mg concentrations obtained from heparinized blood and defibrinated blood. RESULTS Coefficients of variation of the several determination steps used in the MBC- and RBC-assay were < or = 5.4%. The overall analytical variation was 5.0-6.8%, and reproducibility of the complete Mg-assay 11.6-14.0%. Mg measurements in MBC (expressed as fmol/cell) obtained from heparinized blood showed significantly higher values than those obtained from defibrinated 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 removal of platelets is essential in the determination of Mg in MBC.