Can one really measure magnesium deficiency using the short‐term magnesium loading test?

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Abstract
Rob PM, Dick K, Bley N, Seyfert T, Brinckmann CH, Höllriegel V, Friedrich HJ, Dibbelt L, Seelig MS (Medizinische Uniersität zu Lübeck, Freie Universität Berlin, Germany and University of North Carolina, Chapel Hill, USA). Can one really measure magnesium deficiency using the short-term magnesium loading test? J Intern Med 1999 246: 373–378. Objective. To compare a 1-h-version of a magnesium-loading-test (MLT) designed for outpatients in healthy controls with the 8-h standard; to establish the test in patients after renal transplantation prone to develop magnesium (Mg) deficiency; to correlate femur Mg-concentration and percentage retention of the given load. Design. Comparision of mean values from healthy controls with respective from the literature; a prospective, randomized, controlled 4-month study; an intra-individual correlation of Mg-serum values and loading-test data with femur-Mg concentrations. Setting. One centre study in a medical university; outpatients from the transplant unit; inpatients from the orthopedic unit. Subjects. Twenty-four healthy controls aged 36.7 ± 7.4 years; 34 patients after renal transplantation (46.5 ± 14.3 years); 41 patients with hip replacement therapy (63.9 ± 18.6 years). Intervention. Baseline Mg values were measured by atomic absoprtion spectroscopy (AAS) in serum and urine. An intravenous Mg load with 0.1 mmol Mg-aspartate hydrochloride per kilogram bodyweight was given during 1 h. In 24 h-urine, the amount of excreted Mg was measured by AAS and the percentage retention of the given load calculated according to the formula: 1 −[Mg 24 h-urine/Mg test dose] × 100. Femur Mg was measured by AAS in a peace of the femur neck. Patients after renal transplantation were randomized after the first Mg load to either obtain daily 5 mmol Mg-aspartate hydrochloride per kilogram bodyweight, or placebo. Four months later a second loading-procedure was performed. Main outcome measure. Serum Mg, percentage retention of the given Mg load (%Ret) and femur Mg concentration. Results. Mean serum Mg values were within the normal range. In controls, %Ret was –18 ± 21 and not different from the literature. In the first MLT after renal transplantation, %Ret was 47 ± 43. In patients under Mg medication it decreased significantly to 16 ± 26, but was 58 ± 27 in the placebo group. Femur Mg concentration was 62.6 ± 20.9 mmol kg–1 dry substance and the corresponding %Ret was 14 ± 28 with r = – 0.7093. Conclusion. The short-term version of the MLT is as good as the standard and was easily applied in outpatients. The indication from the good correlation between bone-Mg and %Ret and a marked decrease in %Ret in patients after Mg medication was that one can really measure magnesium deficiency.