At a Glance
The patient has a very long partial thromboplastin time (PTT) with a normal prothrombin time (PT) without a bleeding history. The patient had major surgery without bleeding. Factor XII deficiency is seen in individuals of Finnish or northern European extraction, but it has been recognized in all ethnic groups. It is autosomal recessive in inheritance. Its deficiency is not associated with bleeding.
What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?
Confirm that the PTT is prolonged and be certain that the patient does not have a lupus anticoagulant. Confirmatory assay is a factor XII assay. If low, an inhibitor to factor XII must be excluded by performing a specific factor XII inhibitor assay (i.e. a mixing study with factor deficient plasma). (Table 1)
Table 1
| APTT | Factor XII |
|---|---|
| >60 sec | <10% |
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?
It must be excluded that the patient is not on anticoagulants, such as unfractionated heparin, enoxiparin, fondapariux, warfarin, hirudin, argatroban, bivalirudin, or dabigatran. Also, a lupus anticoagulant must be excluded.
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What Lab Results Are Absolutely Confirmatory?
The confirmatory test is a factor XII coagulant assay.
What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?
Factor XII coagulant assay is the confirmatory assay. A specialized laboratory can be contacted to perform a factor XII western blot assay.
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?
As mentioned, anticoagulants will interfere with any coagulation assay. Also, elevated plasma lipids and bilirubin will interfere with some instrument-based coagulant assays.
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