A three-stage chromogenic assay for the quantitative determination of unfractionated and low molecular weight heparins in human plasma by measurement of Factor Xa inhibition.
The inhibitory effect of antithrombin III (ATIII) on Factor IIa (thrombin), Factor Xa (fXa) and other coagulation serine proteases in plasma is increased several-thousand fold by heparin. This inhibition accounts for the anticoagulant effect of heparin.