THE RELATIONSHIP OF CALCIUM ION CONCENTRATION TO THE COAGULATION OF CITRATED PLASMA

Abstract

Citrated plasma was recalcified and the coagulation time plotted against Ca++ concn. as calculated from total Ca and total citrate concns. The minimal Ca++ concn. at which coagulation occurred at pH 7-8 averaged 0.35 [plus or minus] s.d. 0.04 mil/ per liter for human plasma and 0.24 [plus or minus] s.d. 0.02 mM per liter for dog plasma. For a given plasma at constant pH the relationship between Ca++ concn. and coagulation time can be expressed by the equation t = K /(Ca++ - m) +n in which t= time, Ca++:=: Ca++ concn. in mM per liter, K is a constant, m is a constant expressing Ca++ concn. for clotting at infinite time, and n is a constant expressing coagulation time at infinite Ca+ + concn. The values of the constants vary for different samples of plasma. At any given Ca++ concn. the minimum coagulation time is observed when the pH is between 7 and 8. A shift of pH beyond these limits in either direction results in an increase in coagulation time, as well as in the minimum Ca++ concn. required for clotting. The effect of change in pH increases with decreasing Ca++ concn.