Relationship between degree of renal failure and impairment of intestinal calcium absorption

The coefficient of true intestinal calcium absorption (a value) was measured by a double radioisotope technique in 29 chronic renal failure patients (serum creatinine levles 2.5-19.5 mg%) aged 20-75 years. The mean log 10 a (+/- standard error) of these subjects (1.197 +/- 0.031) was significantly lower (p less than 0.001) than that of 52 controls (1.532 +/- 0.024), the geometric mean of the renal failure group (15.7%) being approximately half (46%) of that of the controls (33.9%). The decrease of a value of the uremic patients was more pronounced in the younger than in the older subjects as shown by a statistically significant (r = 0.570; p less than 0.001) positive curvilinear, relationship between a value and age. The lowest intestinal calcium absorptions were observed in patients with a serum creatinine level of approximately 11 mg%, the a values increasing progressively with lower or larger than 11 mg% serum creatinine levels, as shown by a statistically significant (r = 0.485; p less than 0.01) parabolic relationship between a value and serum creatinine. The possible mechanism(s) of this relationship are discussed.