Effects of Haemodialysis on Fractional Intestinal Absorption of Calcium in Uraemia

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Abstract
Fractional intestinal absorption of Ca was measured in 41 hemodialysed patients 4 h after an oral dose of 47Ca. Fractional intestinal Ca absorption was 40.3 .+-. 1.9% (SE of the mean) when measured 10-12 h after a hemodialysis session (dialysate Ca concentration: 1.75 mmol/l). This value was significantly lower (P < 0.001) than that in 26 healthy controls (56.8 .+-. 1.8%) and higher (P < 0.05) than that of 35 patients with chronic renal failure treated conservatively (34.5 .+-. 2.1%). In 17 patients, fractional intestinal Ca absorption was measured just before and just after a dialysis session. Pre-dialysis fractional intestinal Ca absorption (33.7 .+-. 3.0%) was not significantly different from fractional intestinal Ca absorption in uremic patients treated conservatively, while after dialysis fractional intestinal Ca absorption had increased significantly to 42.0 .+-. 2.6% (P < 0.001). The transient increase in fractional intestinal Ca absorption observed after dialysis could be related to dialysis induced volume depletion rather than to a vitamin D-dependent mechanism.