The magnesium load test: II. Correlation of clinical and laboratory data in neonates.

Parenteral magnesium load tests were conducted on 91 infants less than one month of age, most of whom had marked hyperirritability and symptoms compatible with the diagnosis of electrolyte imbalance with relative or absolute magnesium deficiency. Most of the patients studied had a 40-hour test, with an eight-hour preload and a 32-hour postload collection of urine. Of 43 premature infants studied, only three retained less than 40 per cent of the load: one was untreated, one had low retention of a second load following a course of therapy, and the mother of the third had received magnesium within 24 hours of delivery. Of 48 full-term infants studied, ten retained less than 40 per cent of the load. These were asymptomatic or had minor problems. Irritability was common in both high and low retention groups. Ten per cent of the low retention group and 50 per cent of the high retention group manifested two or more of the nonspecific signs compatible with the diagnosis of magnesium deficiency; the difference was significant (P smaller than 0.025). Eleven premature and six full-term infants with very high initial retention received five or six intramuscular injections of magnesium, after which the magnesium retention was about 30 per cent lower than the initial value. For most patients, repletion therapy was given orally. Although low plasma magnesium values related to high magnesium retention, correlation on an individual basis was poor. The plasma calcium levels of three patients with combined hypomagnesmia and hypocalcemia failed to respond to calcium therapy and remained low until the plasma magnesium value was corrected. Magnesium appeared to be specific therapy for symptomatic infants found to be deficient. More males than females had sufficient symptoms to warrant study.