At a Glance
Factor VII deficiency is an inherited bleeding disorder associated with decreased levels of procoagulant factor VII. Factor VII, when appropriately cleaved, forms activated factor VIIa, the trigger of physiological blood clot formation. Deficiency of the factor VII protein, encoded by an autosomal gene on chromosome 13, normally does not cause bleeding manifestations, unless a mutant factor VII gene is inherited from both parents.
One of the most common discoveries of factor VII deficiency results after thorough assessment of the laboratory value of an increased prothrombin time (PT). The clinical phenotype of true factor VII deficient patients is heterogenous and causes asymptomatic disease to severe life-threatening bleeding. When bleeding symptoms do occur from factor VII deficiency, the specific manifestations seen, in decreasing order of occurrence, include:
menorrhagia
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epistaxis
easy bruising
gum bleeding
hemarthrosis
muscle hematoma
gastrointestinal hemorrhage and central nervous system (CNS) bleeding
postoperative bleeding
Uncommon but reported cases of thrombosis may occur with surgery, with replacement therapy, or may happen spontaneously.
What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?
In confirming a suspicion of factor VII deficiency, the ordering clinician should ensure that a fresh sample has been collected and tested within the allotted time requested by the testing laboratory. After confirming the presence of a properly collected intact specimen, an elevated PT with a normal activated partial thromboplastin time (PTT) is consistent with suspicion of factor VII deficiency. Factor VII: coagulant activity (FVII:C) assay is necessary for evaluating the FVII level to rule in or rule out factor VII deficiency. In addition, it should be verified that the patient does not currently take a medication, such as warfarin, associated with decreased FVII:C. (Table 1)
Table 1
| Decreased Factor VII: Coagulant Activity | Normal PTT |
|---|---|
| Type I deficencies result from decreased synthesis of a functional molecule, whereas type II deficencies result from dysfunctional molecules. | An Increased PTT with an elevated PT suggest either warfarin consumption or Vitamin K deficiency, liver disease or deficiency of (a) different protein(s) in the common pathway. |
Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications – OTC drugs or Herbals – that might affect the lab results?
Numerous problems frequently arise because of incorrectly collected or deteriorated specimens. The appropriate ratio of anticoagulant to blood in the testing vessel is also essential. Additionally, the correct anticoagulant solution must be utilized for clinical coagulation times, such as the PT and FVII:C. Most testing sites use 3.2% sodium citrate as the anticoagulant of choice. Although other anticoagulants, such as ethylenediaminetetraacetic acid (EDTA) and/or heparin, are used for some laboratory tests, this is not the case for factor VII testing.
In addition to the patient’s own factor VII protein, the particular thromboplastin utilized by the testing laboratory is a key component in the result obtained. Thromboplasin is the substance that contains the specific cofactor protein “Tissue Factor” that, together with activated factor VII, forms the triggering procoagulation enzyme. Because the particular thromboplastin utilized by many laboratories may be made using a nonhuman tissue factor protein, the possibility of a person’s polymorphic factor VII amino acid 304 termed factor VII Padua may result in a decreased FVII:C that does not result in clinically deleterious physiology.
What Lab Results Are Absolutely Confirmatory?
To determine FVII:C in the clinical laboratory, an inhibitor screen test, frequently termed a “mixing study,” may be performed. In this test, the FVII:C is assessed using a dilution with 1:1 plasma dilution of the patient’s plasma with plasma devoid of any factor VII. Thus, 50% of the FVII will be provided by the patient’s plasma.
What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?
When necessary, factor VII: antigen (FVII:Ag) may be assessed with a specific FVII antigen assay.
Additional specific tests for levels of fibrinogen, thrombin and factor V may be helpful to eliminate a problem with the synthetic function of the liver.
Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications – OTC drugs or Herbals – that might affect the lab results?
Genotyping may be appropriate for counseling and prenatal diagnosis.
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