At a Glance
Inhibitors to factor XI have been reported. Most commonly, they are seen in factor XI deficient patients who have had bleeding and who have required previous fresh frozen plasma replacement. Spontaneous specific inhibitors to factor XI have been seen in patients with lupus anticoagulants. Inhibitors to factor XI promote bleeding, especially from surgical procedures on mucous membranes (e.g., bladder, oral mucosa). Such inhibitors need to be respected and treated.
What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?
Tests valuable to confirm the diagnosis include APTT greater than 45 seconds and a specific inhibitor assay to factor XI. (Table 1)
Table 1
| APTT | Factor XI Assay | Factor XI Inhibitor Assay |
|---|---|---|
| >45 sec | <30% | mixing normal plasma with the patient plasma and then assaying for factor XI |
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 of any sort (i.e., unfractionated heparin, enoxiparin, fondapariux, hirudin, argatroban, bivalirudin, and dabigatran) interfere with any factor XI coagulant assay.
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What Lab Results Are Absolutely Confirmatory?
Laboratory test results that are confirmatory include a low factor XI assay and evidence for a specific factor XI inhibitor on an inhibitor assay.
What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?
-
Low factor XI assay
-
Evidence for a specific factor XI inhibitor on a specialize inhibitor assay
-
No evidence for a lupus anticoagulant
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, hyperlipidemic states and elevated bilirubin affect lab results.
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