Abstract
Calcium absorption was measured in 37 patients, 23 with azotemia not treated with hemodialysis and 14 on hemodialysis. Nine of the 14 were also studied after dialysis. Simultaneous measurements of serum calcium, serum phosphorus, blood urea nitrogen (BUN), serum creatinine, estimated usual calcium intake, and recorded time on dialysis treatments were obtained. In nondialyzed patients, when the BUN concentration was low, calcium absorption was negatively correlated with the BUN; at higher BUN levels, calcium absorption was normal or elevated. Mean calcium absorption in hemodialysis patients was significantly below normal before dialysis and not significantly different from normal after dialysis; however, the data were variable and no conclusion may be reached. Fractional calcium absorption was higher in patients with lower dietary calcium intakes which suggests that these patients retained the ability to regulate calcium absorption in response to body calcium needs. Higher fractional absorption was seen in patients who had been on chronic hemodialysis treatments for longer periods of time. While defective calcium absorption tends to be present in uremic patients, it is not an invariable finding; severe uremia may coexist with supernormal absorption.