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

Background: Intestinal strontium absorption is becoming accepted as a clini cal and diagnostic tool for assessing intestinal calcium absorption in huma ns. 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 me asured in eight healthy men, ages 20-60 years. Before administration of cal citriol, two tests were performed with an interval of 10 days for calculati ng the within-subject variation (SER). Before the third test, 0.5 mu g of c alcitriol was given twice daily for 3 days. In each test, the fractional st rontium absorption (Fc(240)) and the area under the concentration-time curv e (AUC(0-240)) 4 h after an oral strontium load of 2.5 mmol were calculated . Results: The within-subject SER of Fc(240) and AUC(0-240) was 1.7 +/- 0.7 a nd 0.83 +/- 0.1, respectively. The stimulatory effect of calcitriol on Fc(2 40) 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 Fc(240), the Fc(240) 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 Clinic al Chemistry.