Factor VII Antigen Assay

Coagulation

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Description

Factor VII antigen may be used to help fully characterise the deficiency type in subjects with heritable factor VII deficiency.

Factor VII is a vitamin K dependent clotting factor, which shares many features with the other vitamin K dependent factors (i.e. II, VII, IX, X and Protein S). Factor VII is synthesised in the liver and requires vitamin K to complete the synthesis of the physiologically competent proenzyme.

Factor VII activity is reduced in liver disease and also reduced in vitamin K deficiency and in the presence of oral anticoagulation by vitamin K antagonists such as warfarin. Under these latter two conditions, a Factor VII deficient in calcium binding sites appears in the peripheral blood - this is PIVKA VII which can be demonstrated by a low ratio of Factor VII coagulant activity to Factor VII antigen in plasma. In anticoagulated patients, the Protein C antigen can be compared (by ratio) to antigen levels of two other vitamin K dependent clotting factors (usually factors VII and X) to indicate whether PC deficiency is likely or unlikely. However, guidelines recommend against measuring protein C in these patients because results have reduced power to detect protein C deficiency.

FVII antigen assay may be used to help characterise FVII deficiency type in subjects with inherited FVII deficiency.

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Indications

Investigation of heritable FVII deficiency. Detection of type 1 protein C deficiency in subjects who have been on Warfarin for several weeks and have stable INR within the therapeutic range. However, testing for protein C and protein S deficiency whilst on warfarin may not be reliable and is not recommended.

The assay incorporates blocking agent to minimise the influence of Rheumatoid factor that can cause ‘non-specific binding’ in ELISA assays; rarely, assays may be affected and results falsely increased. If this affect is suspected, the laboratory will attempt to remove the affect or may be unable to report the FVII antigen level. 

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Sample Type

Plasma (Citrate Blue) x 1

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Reference Range

Reference range indicated on the report.

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Turnaround Time

Within 4 weeks

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Testing Frequency

Monthly.

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External Notes

A low ratio of PCag/FVIIag or PCag/FXag on at least two occasions can suggest protein C deficiency. Family studies may be required to confirm or deny the diagnosis which is made by a consultant Haematologist.

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Patient Preparation

No special requirements.

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See Also

Protein C Antigen, FX Antigen

Please note: the above information is subject to change and we endeavour to keep this website up to date wherever necessary.