Magnesium levels in critically ill patients - What should we measure?

We studied the relation between ionized magnesium, total magnesium, and alb umin levels in serum of 115 critically ill patients and the role of extrace llular and intracellular magnesium in outcome prediction, Levels of serum t otal and ionized magnesium, serum albumin, and magnesium in mononuclear blo od cells and erythrocytes were measured and the APACHE II score and 1-month mortality recorded. Of all patients, 51.3% had a serum total magnesium concentration below the reference range, In 71% of these hypomagnesemic patients, a normal ser-um i onized magnesium concentration was measured None of the patients had an int racellular magnesium concentration below the reference limit. Except for se rum total and ionized magnesium, none of the magnesium parameters correlate d significantly with each other A significantly negative correlation was fo und between serum albumin and the fraction ionized magnesium. There was no association between low extracellular or intracellular magnesium and clinic al outcome. The observation of hypomagnesemia in critically ill patients depends an whi ch magnesium fraction is measured. The lack of correlation with clinical ou tcome suggests hypomagnesemia to be merely an epiphenomenon. Reliable conce ntrations of serum ionized magnesium can be obtained only by direct measure ment and not by calculation from serum total magnesium and albumin.