SummaryWe studied secretory parathyroid function in 16 newborn infants, aged 34-137 hr, before, during, and after exchange transfusion with a radioimmunoassay recognizing mainly intact human parathyroid hormone-(1-84) ). Before the exchange transfusion, serum calcium was normal or decreased, whereas parathyroid hormone (PTH) was within or above the range of normal adults. Serum P T H approached a maximum at decreased serum ionized and total calcium levels which were close to the normal range. During the early period of the exchange transfusion, serum ionized calcium was decreased as a result of the administration of considerable amounts of phosphate and citrate i n the donor-blood and P T H was raised to levels seen in hypocalcemic infants before the exchange transfusion. Thereafter, serum ionized calcium remained low, whereas mean PTH concentrations were below basal levels. These inappropriately low P T H levels in relation to lowered serum-ionized calcium concentrations are probably the result of inadequate P T H secretion, which is enhanced by withdrawal of large-amounts of presumably biologically active PTH-(1-84) during the exchange transfusion. Serum total calcium.. .on the other hang, was rais& during the exchange transfusion probably as a result of calcium mobilization, and the net calcium balance expressed as the difference of calcium administered and in the withdrawn blood was negative. Even though serum ionized calcium decreased to levels below 2.5 mg/dl during the exchange transfusion, tetany was never observed, iv injections of calcium during the exchange transfusion caused temporary increases in total, but not i n ionized calcium levels and shortening of Q-oTc intervals lasting for less than 1 min. We, therefore, advocate that iv calcium injections at regular time intervals during the exchange transfusion with donor blood preserved in citrate and phosphate should no longer be recommended as a prophylactic measure for preventing the decrease in serum-ionized calcium.
SpeculationParathyroid secretory function is inversely related to serum calcium concentrations i n newborn infants. Serum PTH secretion is maximal at serum-ionized and total calcium concentrations close to the normal range despite further reduction to more markedly hypocalcemic levels. ran sit or^ hypoparathyroidism occurs during exchange transfusion as a result of the removal of considerable amounis of biologically active PTH-(1-84).Evidence obtained by David and Anast (10) indicates that serum PTH is low or undetectable during the first 48 hr of life, whereas after 48 hr, there are parallel increases in PTH as well as in total and ionized calcium levels. In newborn infants, exchange transfusion with donor blood preserved in citrate, or citrate and phosphate are used to relieve hyperbilirubinemia (12,21,35,36). This results in a decrease in ionized (1 1, 27, 33) and in a slight increase in total calcium concentrations (1 1, 27). The available evidence indicates that a fall in ionized rather than in total calcium is responsible for a s...