COUPLED AMIDOLYTIC ASSAY FOR FACTOR-VII - ITS USE WITH A CLOTTING ASSAY TO DETERMINE ACTIVITY STATE OF FACTOR-VII

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  • 1 January 1978
    • journal article
    • research article
    • Vol. 52  (5) , 978-988
Abstract
A coupled amidolytic assay for factor VII (VII) was developed which when used with a clotting assay for VII enables detection of activated VII. In the assay, VII in a test material determines generation of factor Xa in a mixture of purified factor X, tissue factor and calcium. Factor Xa is measured with a chromogenic substrate. Factor VII activity in the coupled amidolytic assay (VIIam) correlated well with VII activity in a 1-stage clotting assay (VIIc) in 57 healthy subjects, 5 patients with hereditary VII deficiency and 11 patients with liver disease. Activation of plasma VII by kaolin, clotting or cold strikingly increased VIIc but not VIIam levels. The ratio VIIc/VIIam (VII activity ratio) is a measure of VII activation. In 27 warfarin-treated patients the mean VII activity ratio was significantly decreased, reflecting a greater decline in VIIc than in VIIam. This probably stems from partially carboxylated VII being able to act during the 3 min incubation of the amidolytic assay but unable to act rapidly enough to affect the clotting assay. Measurement of VIIc/VIIam should enable evaluation of the activity state of VII in thrombotic disorders and in components for transfusion therapy.

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