Dose-response relationship between plasma ionized calcium concentration and thrombelastography.
OBJECTIVE
To establish the threshold value for calcium at which coagulation commenced and to investigate the range over which changes in ionized calcium influenced coagulation.


METHODS
Controlled, nonblinded, in vitro observational study.


METHODS
The study was conducted in a university-based laboratory.


METHODS
Blood was obtained from healthy volunteers.


METHODS
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 (Ca(2+)).


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 Ca(2+) < 0.33 mmol/L showed any clot formation. Normal coagulation measures were obtained in almost all samples in which the Ca(2+) was >0.56 mmol/L. Final clot strength appeared to be independent of Ca(2+) once the threshold value of 0.33 mmol/L was exceeded.


CONCLUSIONS
Ca(2+) of <0.33 mmol/L is necessary to prevent coagulation. Ca(2+) > 0.56 is unlikely to be the cause of coagulation abnormalities during surgical procedures in which calcium metabolism is deranged. Between these values, Ca(2+) may exert an effect on the rate of clot formation, but final clot strength should be unaffected.
James
Michael F M
MF
Department of Anaesthesia, Groote Schuur Hospital and University of Cape Town, Western Cape, South Africa. james@cormack.uct.ac.za
Roche
Anthony M
AM
D001777:Blood Coagulation / Q000187:drug effects* / Q000502:physiology; D002118:Calcium / Q000097:blood*; D002122:Calcium Chloride; D006801:Humans; D066298:In Vitro Techniques; D012016:Reference Values; D012044:Regression Analysis; D013916:Thrombelastography / Q000379:methods*; D013997:Time Factors; D014914:Whole Blood Coagulation Time / Q000379:methods
D002122:Calcium Chloride; D002118:Calcium