Sodium Bicarbonate Infusion Test: A New Method for Evaluating Parathyroid Function

Abstract

Abstract. We have developed a new test for estimating the secretory capacity of parathyroid hormone (PTH) from the parathyroid gland. Sodium bicarbonate solution [8.4% (w/v); 35 ml/m 2 body surface area] was infused for 2 min, and blood samples for the determination of plasma ionized calcium, plasma PTH (intact, midregion, carboxy-terminus) and related parameters were serially obtained. In 8 healthy volunteers, the mean (±SE) plasma ionized calcium fell promptly and significantly (from 1.21 ± 0.01 to 1.11 ± 0.01 mmol/L) after the sodium bicarbonate infusion. The mean (±SE) plasma intact PTH increased promptly and significantly, by more than four fold (42.3 ± 4.2 to 182.4 ± 34.7 pg/ml), and then gradually returned to basal levels. In patients with partial hypoparathyroidism who have detectable basal plasma levels of PTH, the absolute increment in PTH levels was much less, and in the plasma obtained from patients with complete hypoparathyroidism, absolutely no response was observed. Plasma obtained from patients diagnosed with primary hyperparathyroidism (parathyroid adenoma or hyperplasia) has high basal PTH levels. The response to the sodium bicarbonate infusion in these patients was markedly blunted (less than a two-fold increase in all cases examined). No significant adverse effects were observed during the procedure. Therefore, the sodium bicarbonate infusion test is a simple and sensitive method to stimulate PTH release, and is clinically useful for evaluating parathyroid gland function.

Evaluation of Parathyroid Gland Function Using Sodium Bicarbonate Infusion Test for 22q11.2 Deletion Syndrome

“…2 Effects of sodium bicarbonate infusion on plasma intact PTH levels in 5 patients. The dotted line shows the mean response in healthy volunteers according to a previous report [8]. …”

“…A NaHCO 3 infusion test, the new method for evaluating parathyroid function, showed that a prompt and brisk rise in plasma PTH occurred following a minimal decrease in plasma ionized calcium and an increase in blood pH in healthy subjects [8]. The mean (±SE) plasma intact PTH levels increased promptly and significantly more than fourfold (42.3 ± 4.2 to 182.4 ± 34.7 pg/ml), and gradually returned to basal levels in healthy subjects [8].…”

“…The NaHCO 3 infusion test was performed in accordance with previously reported methods [8]. In fasting states, NaHCO 3 solution [7% (w/v); 40 ml/body surface area (m 2 ), maximal dose 40 ml] was infused for 2 min, and blood samples for the determination of plasma ionized calcium and plasma intact PTH were serially obtained at 0, 3, 5, 10, 30 and 60 min following the start of infusion.…”

“…In fasting states, NaHCO 3 solution [7% (w/v); 40 ml/body surface area (m 2 ), maximal dose 40 ml] was infused for 2 min, and blood samples for the determination of plasma ionized calcium and plasma intact PTH were serially obtained at 0, 3, 5, 10, 30 and 60 min following the start of infusion. Referring to a previous report [8], an increment in PTH levels (peak value – basal value) of 50 pg/ml or higher during the test was defined as normal parathyroid gland function, and any lower levels were defined as subclinical hypoparathyroidism.…”

“…Ethylenediaminetetraacetic acid loading was used to analyze parathyroid gland function [3,6,7], but it is not widely performed because of adverse effects. A sodium bicarbonate (NaHCO 3 ) infusion test is a new method for evaluating parathyroid gland function [8]. NaHCO 3 is a weak alkali agent, and ionized calcium decreases with a rise in pH when it is administered, which in turn potently stimulates the release of PTH.…”