Overall haemostasis potential assays performed in thrombophilic plasma: the effect of preactivating protein C and...

The overall haemostatic potential (OHP) assay records fibrin polymerisation in plasma by areas under the opacity curve. The authors reported high area values in pregnancy, and still higher values in preeclampsia. We wanted to see if the assay detects thrombophilia, and particularly, if the area values were high in congenital combined protein S (PS) and the FV R506Q Leiden mutation, since low protein S and increased activated protein C (APC) resistance occur in pregnancy and preeclampsia.

The original overall haemostatic potential assay and our modified version with Protac and pentasaccharide to enhance inhibition by activation of protein C and by antithrombin (AT) were performed in plasma from 18 persons with thrombophilia. Seven had combined protein S deficiency and heterozygous FV Leiden mutation.

In the original assay, median area values in controls and thrombophilic plasma samples were similar. In the modified assay, area values tended to be lower in controls than in the thrombophilia group (P=0.035). The enhanced inhibition reduced area values more in control plasmas (median reduction 34.7%) than in thrombophilic plasmas (median reduction 2.2%) (P=0.0017). The responses to activation were also low in warfarin-treated patients with thrombophilia.

High area values in pregnancy with the original assay are probably not caused by insufficient inhibition. The response to activation of protein C and antithrombin, as calculated by the difference between the original and a modified assay, was subnormal in thrombophilic plasma, but there was an overlap with the results in controls.