Defibrination essential in the assay of ionized magnesium in mononuclear cells.

Intracellular free (ionized) magnesium concentration was measured in mononuclear cells isolated from healthy volunteers by use of dual wavelength fluorescence (indicator: mag-fura-2). We found a free Mg2+ concentration of 1.28 +/- 0.08 mmol/l in mononuclear cells isolated from heparinized blood. When we defibrinated blood samples prior to the isolation step we measured 0.78 +/- 0.05 mmol/l of free Mg2+ in these cells. We conclude that this difference is caused by the platelets present in the heparinized specimens.