A study was performed to assess the value of estimation of intracellul
ar magnesium content. A magnesium loading test was used to diagnose ma
gnesium depletion in critically ill patients. Patients were divided in
to magnesium depleted and non-depleted groups according to their respo
nse to the loading test. Pre-infusion plasma and intracellular (blood
cell) magnesium levels were measured. There were no significant differ
ences between the magnesium depleted (mean plasma magnesium 0.81 mmol.
l(-1), red blood cell magnesium 2.34 mmol.l(-1), mononuclear blood cel
l magnesium 25.16 mmol.kg(-1) dry weight) and non-depleted groups (mea
n plasma magnesium 0.90 mmol.l(-1), red blood cell magnesium 2.18 mmol
.l(-1), mononuclear blood cell magnesium 18.1 mmol.kg(-1) dry weight).
We conclude that the diagnosis of magnesium depletion cannot be exclu
ded in the face of normal plasma, red blood cell or mononuclear blood
cell concentrations of magnesium.