Citrate anticoagulation and divalent cations in hemodialysis.

Anticoagulation with citrate in combination with a calcium-free, magnesium-containing dialysate (Ca-Mg+) and intravenous supplementation of calcium is a safe procedure in renal failure patients at high risk of bleeding. Since magnesium may antagonize the anticoagulant effect of citrate by forming complexes with citrate, we studied the in vitro and in vivo interactions of calcium and magnesium on citrate anticoagulation. In the in vitro studies the activated partial thromboplastin time (APTT) was 88 s, both after addition of 3.0 mumol magnesium and after addition of 1.0 mumol calcium. The combination of 2.4 mumol magnesium and 1.0 mumol calcium achieved similar APTT values of about 35 s as 3.5 mumol calcium alone. Moreover, in a Lee-White blood clotting time, the anticoagulant effect of 7 mumol citrate was neutralized by either 10.5 mumol of a mixture of the two cations or 10.5 mumol calcium chloride alone. In 6 chronic hemodialysis patients the in vivo interactions of calcium and magnesium on citrate were measured. At the dialyzer outlet, the whole blood activated clotting time (ACT) was significantly (p < 0.05) shorter during dialysis with a Ca-Mg+ dialysate than during dialysis with a calcium- and magnesium-free dialysate (Ca-Mg-). With the Ca-Mg- dialysate the ACT at the dialyzer outlet was still significantly longer than the ACT in the arterial line before citrate infusion. We also compared the serum concentrations of calcium and magnesium during the Ca-Mg- dialysate which was used in combination with intravenous calcium and magnesium supplementation - 0.18 and 0.08 mmol/min respectively--and during a conventional calcium- and magnesium-containing dialysate (Ca+Mg+).(ABSTRACT TRUNCATED AT 250 WORDS)