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Strontium as a Marker for Intestinal Calcium Absorption: The Stimulatory Effect of Calcitriol

¹ Department of Endocrinology and
² Clinical Research Laboratory of Internal Medicine, University Hospital Vrije Universiteit, De Boelelaan 1117, 1081 HV Amsterdam, The Netherlands.
^a Address correspondence to this author at: University Hospital Vrije Universiteit, Room Br 232, De Boelelaan 1117, 1081 HV Amsterdam, The Netherlands. Fax 31-20-4443844; e-mail M.tenBolscher{at}azvu.nl

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 (AUC^0–240) 4 h after an oral strontium load of 2.5 mmol were calculated.

Results: The within-subject SE_R of Fc₂₄₀ and AUC^0–240 was 1.7 ± 0.7 and 0.83 ± 0.1, respectively. The stimulatory effect of calcitriol on Fc₂₄₀ and AUC^0–240 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 AUC^0–240 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.