Can one really measure magnesium deficiency using the short-term magnesiumloading test?

Objective. To compare a 1-h-version of a magnesium-loading-test (MLT) desig ned for outpatients in healthy controls with the 8-h standard; to establish the test in patients after renal transplantation prone to develop magnesiu m (Mg) deficiency; to correlate femur Mg-concentration and percentage reten tion of the given load. Design. Comparision of mean values from healthy controls with respective fr om 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 tra nsplant 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 re placement therapy (63.9 +/- 18.6 years). Intervention. Baseline Mg values were measured by atomic absoprtion spectro scopy (AAS) in serum and urine. An intravenous Mg load with 0.1 mmol Mg-asp artate 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 ret ention of the given load calculated according to the formula: 1 - [Mg 24 h- urine/Mg test dose] x 100. Femur Mg was measured by AAS in a peace of the f emur neck. Patients after renal transplantation were randomized after the f irst Mg load to either obtain daily 5 mmol Mg-aspartate hydrochloride per k ilogram bodyweight, or placebo. Four months later a second loading-procedur e 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, %R et was -18 +/- 21 and not different from the literature. In the first MLT a fter renal transplantation, %Ret was 47 +/- 43. In patients under Mg medica tion it decreased significantly to 16 +/- 26, but was 58 +/- 27 in the plac ebo group. femur Mg concentration was 62.6 +/- 20.9 mmol kg(-1) dry substan ce and the corresponding %Ret was 14 +/- 28 with 0.7093. Conclusion. The short-term version of the MLT is as good as the standard an d was easily applied in outpatients. The indication from the good correlati on between bone-Mg and %Ret and a marked decrease in %Ret in patients after Mg medication was that one can really measure magnesium deficiency.