Role of magnesium loading test in detecting hypomagnsemia in critically ill Patients

Magnessium [Mg] deficiency has not usually been considered in clinical practice due to lack of relevant blood tests and because the symptoms are often vague and non-specific. Serum concentrations may not adequately reflect Mg status. Mg Loading Test [MLT] can provide information on total body Mg stores. We prosectively studied 21 critically ill patients [10 males, 11 females] admitted to the ICU, to investigate the prevalence of Mg deficiency. Their mean age was 50 +/- 21 years. To determine serum Mg, venous blood specmens were obtained just before the MLT. Mg sulfate [30 mmol] was infused during an 8-hr period and 24-hr urine samples were collected from the starting of Mg infusion. Although low serum Mg [<1.8 mmol/L] was present only in 2 patients, MLT showed Mg deficiency in 18 patients. MLT detected Mg deficiency in 13 out of 14 patients with normal serum Mg, in 2 out of 2 subjects with hypomagnesemia, and in 3 out of 5 cases with hypermagnesemia. Of 7 fetal cases, 6 occurred in individuals with hypomagnesemia [6/18] and 1 death occurred in the normomagnesemic group [1/3]. There was no relationship between Mg retention, age [r=0.33, p=0.63] and serum Mg concentrations [r=0.15, p=0.925]. There was a significant correlation between Mg uptake and APACHE II score [r=0.46, p=0.035]. In conclusion, Mg depletion is highly prevalent in ICU patients according to MLT. MLT is superior to serum Mg in determining actual Mg status in this group. Therefore, we suggest that MLT, and not serum Mg, should be carried out in patients when Mg deficiency is suspected