Effects of hemodialysis on protein-bound calcium

This study evaluates whether hemodialysis alters the affinity of plasma proteins for calcium. We have used a new automated methodology for the determination of the dialyzable calcium fraction. Protein-bound calcium was estimated as the difference between the total and dialyzable calcium fractions. All measurements were made after adjustment of the sample pH to 7.40 +/- 0.02. The calcium fractions were determined in 12 patients before and after hemodialysis. In addition, we added calcium to the predialysis specimens to evaluate the effect of increased ionic calcium on protein binding and corrected the protein-bound calcium in these specimens for the increase in total protein observed in the postdialysis specimens. Hemodialysis significantly increased total, dialysable, and protein-bound calcium. The mean ratio of protein-bound calcium in the postdialysis specimens to the corrected protein-bound calcium in the predialysis specimens with calcium added was 0.97 +/- 0.02. We conclude that (1) the increase in protein-bound calcium to the predialysis specimens, and that (2) the binding affinity of serum proteins for calcium is not altered by hemodialysis.