Plasma ionized magnesium in tubular disorders with and without total hypomagnesemia

Selective electrodes have been designed for determining plasma ionized magnesium. In kidney disease the relationship between ionized and total circulating magnesium is often altered. Hence plasma ionized magnesium (ETH 7025 membrane) was determined in 25 patients with primary renal tubular disorders; 6 patients had total hypomagnesemia. Total plasma magnesium was never reduced in the remaining 19 patients. Plasma ionized magnesium values were low in the 6 patients with total hypomagnesemia. In 18 of the 19 patients without total hypomagnesemia plasma ionized magnesium values were not reduced. Ionized hypomagnesemia was noted in a patient with normal total plasma magnesium in the context of hypercalciuric nephrocalcinosis of unknown origin. The study demonstrates an excellent concordance between plasma total and ionized magnesium in tubular disorders associated with total hypomagnesemia and a good concordance in tubular disorders that are not linked with total hypomagnesemia. The determination of circulating ionized magnesium is of little value in the diagnostic work-up of the vast majority of renal tubular disorders. The determination might perhaps disclose latent hypomagnesemia in nephrocalcinosis of unknown cause.