LabMed

Factor XI Deficiency – Congenital

At a Glance

Factor XI deficiency is a bleeding disorder frequently associated with mucosal bleeding. It is autosomal recessive in inheritance. It is frequently seen in the Ashkenazi Jewish population of eastern European origin (~50% in the United States), but it has been associated with every ethnic group. It can be quite dormant in most patients and is usually picked up by a prolongation of the partial thromboplastin time (PTT). It is usually not associated with spontaneous hemarthosis but is associated with surgical bleeding.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

Tests useful to confirm a clinical diagnosis include PTT greater than 45 seconds and a low factor XI assay with no evidence of an inhibitor to factor XI or a lupus anticoagulant. (Table 1)

Table 1

Test Results Indicative of the Disorder
APTT Factor XI Assay
>45 sec <30%

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?

Any anticoagulant, such as heparin, enoxiparin, fondaparinux, warfarin, hirudin, bivalirudin and dabigatran, will interfere with factor XI coagulant assays. Lupus anticoagulants will also interfere with assay.

What Lab Results Are Absolutely Confirmatory?

Low factor XI coagulant assay with no evidence of an inhibitor to factor XI or a lupus anticoagulant is absolutely confirmatory.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

Tests useful to confirm a clinical diagnosis include Factor XI coagulant assay and inhibitor to factor XI. Any other assay is in the realm of the research laboratory.

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?

Anticoagulants, hyperlipidemia and hyperbilirubin affect lab results.

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