Plasma calcium fraction dynamics in uremic patients undergoing hemodialysis.

22 patients with chronic renal failure, maintained on chronic maintenance dialysis with a dialysate calcium of 1.5 mmol/l, were randomly selected for measurement of pre- and postdialysis plasma calcium fractions. Total, ionized and protein-bound calcium fractions in plasma showed significant increases following dialysis, but with correction for hemoconcentration due to ultrafiltration from dialysis, only protein-bound calcium showed a significant increase. Change of in vitro pH from 7.35 to 7.44 did not influence calcium binding. Similarly, in vitro addition of calcium to pre- and postdialysis blood samples did not result in significant differences for protein-bound calcium fractions. Comparison of dissociation constants for protein-bound calcium between pre- and postdialysis samples showed a significant change. Our results indicate that dialysis alters the affinity of serum protein by some unexplained mechanism and may contribute to the genesis of dialysis-bone disease.