Dose-response relationship between plasma ionized calcium concentration and thrombelastography

Objectives: To establish the threshold value for calcium at which coagulation commenced and to investigate the range over which changes in ionized calcium influenced coagulation. Design: Controlled, nonblinded, in vitro observational study. Setting: The study was conducted in a university-based laboratory. Participants: Blood was obtained from healthy volunteers. Interventions: One hundred samples of citrated blood were recalcified using varying quantities of 10% calcium chloride solution. Heparinized samples from the recalcified blood were obtained for measurement of ionized calcium concentration (Ca2+). Measurements and Results: Coagulation of the recalcified samples was analyzed using thrombelastography. The ionized calcium concentration in recalcified blood was measured using a calcium electrode in a blood gas analyzer. No sample with a Ca2+ < 0.33 mmol/L showed any clot formation. Normal coagulation measures were obtained in almost all samples in which the Ca2+ was >0.56 mmol/L. Final clot strength appeared to be independent of Ca2+ once the threshold value of 0.33 mmol/L was exceeded. Conclusions: Ca2+ of <0.33 mmol/L is necessary to prevent coagulation. Ca2+ > 0.56 is unlikely to be the cause of coagulation abnormalities during surgical procedures in which calcium metabolism is deranged. Between these values, Ca2+ may exert an effect on the rate of clot formation, but final clot strength should be unaffected. (C) 2004 Elsevier Inc. All rights reserved.