Strontium as a marker for intestinal calcium absorption: The stimulatory effect of calcitriol

Abstract

Background: Intestinal strontium absorption is becoming accepted as a clinical and diagnostic tool for assessing intestinal calcium absorption in humans. However, little is known about whether intestinal strontium absorption, like that of calcium, is stimulated by calcitriol in healthy humans. Methods: The effect of calcitriol on intestinal strontium absorption was measured in eight healthy men, ages 20-60 years. Before administration of calcitriol, two tests were performed with an interval of 10 days for calculating the within-subject variation (SE(R)). Before the third test, 0.5 μg of calcitriol was given twice daily for 3 days. In each test, the fractional strontium absorption (Fc240) and the area under the concentration-time curve (AUC0-240) 4 h after an oral strontium load of 2.5 mmol were calculated. Results: The within-subject SE(R) of Fc240 and AUC0-2240 was 1.7 ± 0.7 and 0.83 ± 0.1, respectively. The stimulatory effect of calcitriol on Fc240 and AUG0-2240 was 35% (21.8 ± 2.0 to 28.8 ± 2.4; P = 0.003) and 61% (8.97 ± 0.97 to 14.4 ± 1.3 mmol · L-1 · min; P = 0.001), respectively. Conclusions: Although the reproducibility of AUG0-240 and its sensitivity to calcitriol were better than those of Fc240, the Fc240 of strontium is preferred for a clinical test because of its simplicity, requiring only two instead of five blood samples. (C) 2000 American Association for Clinical Chemistry.