Intestinal absorption of calcium and whole-body calcium retention in incipient and advanced renal failure

Fractional intestinal absorption of Ca (A(ca)) and fractional whole body retention of Ca (R(ca)) were measured in 130 patients with incipient and advanced renal failure. In fasting patients without prior dietary restrictions, A(ca) was measured with a ⁴⁷Ca double-dose technique using a whole body counter. A(ca) was significantly decreased and R(ca) significantly increased in patients with renal failure. A significant correlation between GFR and A(ca) was observed. A defect of Ca absorption was found in some patients with 75 ml/min x 1.73 m² GFR, earlier than reported by previous investigators. R(ca) increased with decreasing GFR and correlated to serum PTH and histological parameters of PTH action on bone. It is suggested that R(ca) represents a useful indicator of bone turnover.