Interaction of calcium ions with serum albumin in chronic renal failure

In order to study the effect of the uremic environment on serum calcium-albumin interaction, ten adult subjects with chronic renal failure (creatinine clearances below 20 ml/min) and five adult normal subjects, had their serum ionic calcium (Orion SS-20) determined at three different serum pH values. At similar serum protein levels, the correlations between serum ionic calcium pH were: (a) normals: number of pairs = 15, r = -0.90, p less than 0.01, Ca2+ = 4.54-0.484 pH. (b) uremics: number of pairs=15, r=-0.97, p less than 0.01, Ca2+=4.02-0.429 pH. These regressions were similar as far as the slopes (Fslope=0.62, p greater than 0.05) but had different intercepts (Fintercepts=64.34, p less than 0.01). These results confirm that uremics, when compared to normal subjects, present an ionic hypocalcemia at any level of serum pH. They also show that serum calcium-albumin interaction is normal in uremia. In view of the above results, it can be suggested that, among several possible causes, alterations in the binding-affinity of calcium ions to serum albumin can be excluded as an additional factor of secondary hyperparathyroidism in uremia.