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.