A New Oral Isotopic Test of Calcium Absorption *

Abnormal absorption of dietary calcium has been recognized for many years in intestinal diseases, sarcoidosis (1), idiopathic hypercalciuria (2), hypoparathyroidism (3, 4), hyperparathyroidism (5-7), and more recently in calcinosis universalis (8). Understanding of calcium absorption in the past has been limited by the requirement of 18 to 20 days of metabolic balance procedures; interpretation has been limited by the paucity of data in normal subjects. This paper describes a safe and simple 4-hour isotopic test of calcium absorption that has been evaluated statistically in 21 normal subjects and in 31 patients with disorders known to alter calcium absorption.