Ionised and total magnesium serum concentrations in renal and hepatic diseases.

Ionised and total magnesium concentrations were determined in the serum of different groups of patients suffering from renal or hepatic diseases. Ionised magnesium was measured by Microlyte 6 (KONE, Espoo, Finland) and total magnesium by atomic absorption spectrometry. In renal insufficiency ionised and total magnesium concentrations were almost equally increased. In proteinuria with a normal glomerular filtration rate, "pseudohypomàgnesaemia" was observed, i.e. decreased total magnesium concentration in parallel with a decreased albumin concentration with no significant change in the concentration of ionised magnesium. Hypermagnesaemia occurred in liver diseases combined with renal insufficiency, whereas "pseudohypomagnesaemia" was most often found in the absence of renal failure. Also treatment with an aldosterone antagonist was associated with a normal ionised magnesium concentration, but the total magnesium concentration was decreased; when additional magnesium was administered, the total magnesium concentration approached a normal value, while ionised magnesium slightly exceeded reference values. Only during cyclosporin treatment did both ionised and total magnesium concentrations become lowered. However, the decrease of total magnesium exceeded that of ionised magnesium due to concomitant hypoalbuminaemia with reduction of the protein-bound fraction. It is concluded that especially low total magnesium concentrations should be investigated by measurement of ionised magnesium to exclude "pseudohypomagnesaemia".