Whole blood clot formation phenotypes in hemophilia A and rare coagulation disorders. Patterns of response to recombinant factor VIIa.

Until now, no routinely used clotting assay has demonstrated the power to reflect significantly a patient's response to recombinant factor (rF)VIIa. Adopting a thrombelastographic principle, profiles of continuous whole blood (WB) coagulation were studied in minimally altered WB activated with a small amount of tissue factor (TF). Investigation of the WB clotting profile was performed before and after ex vivo addition of rFVIIa 20 nm to WB from 26 patients with hemophilia A, two patients with severe hemophilia B, and individuals with deficiencies of FV, FX, FXI, and FXIII. In five patients with hemophilia plus inhibitors, the response to ex vivo added rFVIIa and to activated complex concentrate (APCC) was studied. Patients with severe and moderate hemophilia A demonstrated remarkable variance in the hemostatic characteristics at baseline, even in groups with the same FVIII:C activity levels. The response to rFVIIa at 20 nm also varied extensively, the effect correlating with the continuous WB coagulation phenotype at baseline. This indicates that the efficacy of rFVIIa may be optimized by tailoring the dose according to the hemostatic response to varying doses tested prior to in vivo administration. In patients with inhibitors against FVIII and factor IX, rFVIIa and APCC substitution resulted in quite similar response patterns that appeared to be dose dependent. In severe FV, FX, and FXIII-deficient WB, rFVIIa addition induced minor changes only. In FXI deficiency, rFVIIa normalized the dynamic properties of clotting, although a reduced clot firmness remained unchanged. In conclusion, the thrombelastographic analysis of WB clotting, as activated with a minute amount of TF, seems an interesting method that detects phenotypic variation amongst hemophilia patients. The method appears useful for assessment of the hemostatic capacity and it seems a promising tool for evaluation of the individual response to rFVIIa or APCC before and during in vivo administration.