THE EFFECT OF HEPARIN AND ITS NEUTRALIZATION ON FUNCTIONAL ASSAYS FORFACTOR VIIA, FACTOR-VII AND TFPI

Recently methods have become available to assay the haemostasis protei ns tissue factor pathway inhibitor (TFPI) and activated factor VII (FV IIa). These assays are primarily used in research and in some studies patients may be receiving heparin therapy. We investigated the effect of heparin and its neutralisation by protamine sulphate, hexadimethrin e bromide (polybrene) and triethylaminoethyl (TEAE) cellulose, on func tional assays for TFPI, FVIIa and also factor VII (FVII). In the clott ing assay for FVIIa using truncated recombinant tissue factor, heparin had little effect up to 1 U/ml, but concentrations higher than this g rossly prolonged the clotting time. Protamine and polybrene neutralisa tion of heparin resulted in some prolongation of the clotting time des pite adequate heparin neutralisation, and in addition, in the absence of heparin each of these substances themselves affected the clotting t ime. TEAE neutralisation of heparin appeared to be effective in the FV IIa assay, although in the absence of heparin we observed a 5% decreas e in the clotting time. In the amidolytic substrate assays for TFPI an d FVII, heparin with or without neutralisation resulted in only small changes in the optical density at 405nm and hence plasma levels of the se factors were not significantly changed. Copyright (C) 1996 Elsevier Science Ltd