Mononuclear blood cell magnesium in older subjects: evaluation of its use in clinical practice

Serum and mononuclear blood cell (MBC) magnesium were measured in 24 healthy community subjects, average age 76 years (67-93), and in 21 ill hospitalized subjects, average age 79 years (65-90). MBC magnesium, expressed as mumol/mg protein, was significantly lower in the in-patient group (P < 0.001), but tended to be higher in the same group when expressed as fmol/cell (not significant). Further samples from community subjects on the same day, and again at 7 days, revealed coefficients of variation for intrasubject analysis of 12% and 22%, respectively (fmol/cell). The equivalent intrasubject values for serum were 2.8% on the same day and 4% at 1 week. MBC magnesium values for inpatients were probably distorted by changes in cell size and cell protein content caused by illness. Biological variability and the effects of illness on the composition and size of cells seem to limit the usefulness of MBC magnesium measurement as a clinical tool for assessment of body magnesium status.