Approach Considerations
Laboratory studies
Laboratory studies for suspected hemophilia C should include the following:
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Complete blood count (CBC)
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Measurement of factor XI levels
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Measurement of factor VIII and von Willebrand factor
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Prothrombin time (PT), aPTT, and thrombin time (TT) (usually performed before the measurement of factors)
With regard to the last item, the aPTT is usually prolonged in factor XI deficiency (but depends on the sensitivity of the reagent and test system--partial deficiency can be missed), whereas the PT and TT are normal.
A specific assay for factor XI activity is necessary to confirm the diagnosis. Assays of other clotting factors and platelet function may be needed to exclude a combined hereditary deficiency of factor XI and other factors. In terms of predicting bleeding tendency, findings show that the aPTT test measures factor XI activation via the contact system, which is not the relevant physiologic pathway. Research demonstrates that the thrombin-generation test, under conditions of low tissue factor and with inhibition of contact factors, may give a better indication of the risk of bleeding than the specific factor XI activity assay based on the aPTT. A retrospective study by Désage et al found that among factor XI–deficient operative patients who were not prescribed hemostatic treatment for surgery and had three impaired thrombin-generation assay parameters, 15 out of 34 operations (44%) reportedly led to bleeding. [18, 19]
A study by Gidley et al indicated that bleeding risk in patients with severe or partial factor XI deficiency can be assessed by using turbidity assays to reveal decreased clot formation and reduced fibrinolysis resistance in corn trypsin inhibitor–treated platelet-poor plasma. [20]
Imaging studies
No imaging studies are necessary in diagnosing factor XI deficiency. However, imaging studies may be obtained to evaluate the extent of bleeding in the management of bleeding at any site.
Genetic analysis
Genetic analysis for the mutation in factor XI is helpful in determining which mutation caused the deficiency.
