Mathematical expressions of measuring curves for concentration of clotting factors

Conversion of coagulation time (t) to relative arbitrary substance concentration of coagulation factors (II + VII + X) abbreviated c(ra)) was originally made from a measuring curve corresponding to the equation log t = a(o) +a₁ log c(ra). Three more suitable equations are presented and tested for fit: t = A(o) + A₁ c(ra); t = B(o) + B₁ c(ra) + B₂ c²ra; log t = b(o) + b₁ log c(ra) + b₂ log c(ra)². Their suitability for the Simplastin®-A and Thrombotest® methods is also investigated. The last equation yields the best fit and replaces the error-prone reading of log-log curves by a calculation suitable for routine use.