ELEVATED CIRCULATING IMMUNOREACTIVE PARATHYROID MONE (iPTH) IN PREMATURE INFANTS

Abstract

Serum iPTH was measured in 160 AGA full-term and premature normocalcemic and hypocalcemic infants during the first 96 hours of life. In normal full-term infants, iPTH was low in cord blood and remained low during the first 12 hours of life as serum Ca declined. Thereafter the serum iPTH rose to the mid-normal range. Consistent with our previous studies, in only 20% of serum samples from hypocalcemic full-term infants was iPTH elevated; in the remainder, iPTH was inappropriately low, though usually in the normal detectible range. By contrast, serum iPTH was elevated in 75% of samples of hypocalcemic prematures. Moreover, elevated iPTH was found in approximately 15% and 35% serum samples of normocalcemic full-term and premature infants, respectively. At any given Ca level the serum iPTH appeared to vary inversely with gestational age. The results suggest 1) That parathyroid responsiveness is greater in premature than full-term infants, possibly related to lesser period of exposure to hypercalcemia in utero and 2) That a factor(s) other than parathyroid insufficiency acts in the newborn to reduce plasma Ca; in some infants, compensatory increases in parathyroid activity may be sufficient to maintain normocalcemia, while in others there is either no compensatory increase or the increase is insufficient and hypocalcemia results. It is possible that metabolic clearance of iPTH varies with gestation and accounts, in part, for our findings.

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