Factor VII Deficiency Workup

Updated: Nov 06, 2019
  • Author: Muhammad A Mir, MD, FACP; Chief Editor: Perumal Thiagarajan, MD  more...
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Workup

Laboratory Studies

Routine initial hemostatic tests for suspected factor VII deficiency include the following:

  • Activated partial thromboplastin time (aPTT)
  • Prothrombin time (PT)
  • Platelet count

A normal aPTT and a prolonged PT in a patient with a lifelong history of a tendency for mild or severe bleeding is consistent with the diagnosis of factor VII deficiency or the presence of an inhibitor to factor VII.

Bleeding time is usually within the reference range.

With no significant clinical bleeding but a prolonged PT and a normal aPTT, the patient has either mild factor VII deficiency or is taking oral anticoagulants.

To distinguish between factor VII deficiency and the presence of an inhibitor to factor VII, mixing studies are useful. PT testing is repeated using a 1:1 mixture of the patient's plasma and normal plasma. Normal plasma is a source of factor VII; therefore, when such a mixture normalizes the prolonged PT, the patient likely has a deficiency of factor VII. When the mixture still results in a prolonged PT, sometimes after initial correction, an inhibitor to factor VII is probably present.

A specific assay for factor VII, using known factor VII–deficient plasma, is required to confirm the diagnosis. Factor VII antigen can be measured using a radioimmunoassay.

Functional factor VII assays are as follows:

  • To determine the severity, factor VII activity levels (factor VII:c) are measured using a single-stage, PT-based assay.

  • The factor VII:c assay uses the ability of tissue factor to promote the conversion of factor VII to factor VIIa and measures the total clotting activity of factor VII and factor VIIa. Results can vary dramatically depending on the source of tissue factor used in the in vitro assay.

Immunological factor VII assays can be used to measure factor VII:Ag (antigen levels). This can be an enzyme-linked immunosorbent assay or an immunoradiometric assay.

A factor VIIa:c assay is used to evaluate therapeutic factor VIIa levels. This is an enzyme-linked immunosorbent assay using specific antibodies or soluble mutant tissue factor that is insensitive to native factor VII but that serves as a cofactor for factor VIIa catalyzed activation of factor X.

A more definitive approach involves genetic analysis of mutant genes in involved families.

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Imaging Studies

CT scan and ultrasound have been used to localize, quantify, and serially monitor the location and response of bleeding to specific therapy.

Plain radiography is not useful for evaluating soft tissue damage.

MRI can be used to assess soft tissue damage; is a better modality to evaluate joint effusion, synovial hyperplasia, and cartilage loss; and can help localize the bleeding site. MRI is beneficial for evaluating reversible joint changes for earlier intervention in persons with hemophilia A and B.

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