Laboratory Studies
The prothrombin time (PT) is prolonged in factor VII (FVII) deficiency and the international normalized ratio (INR) is elevated. The activated partial thromboplastin time (aPTT) is within the reference range in isolated factor VII deficiency.
Specific factor VII assays are required for diagnosis.
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Factor VII assays are performed by using a tissue factor (TF; thromboplastin)–dependent, one-stage clotting assay.
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The sensitivity of the assay depends on the choice of assay reagents. The less sensitive animal-derived thromboplastins cannot be used to accurately measure levels less than 5%.
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The more sensitive thromboplastins, usually recombinant human thromboplastin, are preferred for measuring factor VII activity in the very low range.
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When the deficiency is due to mutations that affect formation of the TF/factor VIIa/FX complex, the measured factor VII levels may significantly vary depending on the type of reagent used (ie, rabbit vs human thromboplastin).
Genetic studies, including genotyping, may be warranted for counseling and prenatal diagnosis.
Factor assays in family members are indicated to identify other affected individuals.
Although factor VII levels are statistically lower in "bleeders" than in "nonbleeders," they may not predict bleeding risk in individual patients.
Imaging Studies
Appropriate imaging studies may be useful in the evaluation of suspected bleeding. For instance, CT scanning or MRI of the brain is indicated for suspected CNS hemorrhage.
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Intrinsic and extrinsic pathways of coagulation. Factor VII/tissue factor complex activates factor IX and factor X. Factor IXa along with factor VIIIa results in formation of more factor Xa. Factor Xa along with factor Va converts prothrombin to thrombin.
