Ra. Cardigan et al., THE EFFECT OF HEPARIN AND ITS NEUTRALIZATION ON FUNCTIONAL ASSAYS FORFACTOR VIIA, FACTOR-VII AND TFPI, Thrombosis research, 84(4), 1996, pp. 237-242
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