Platform
Company
Coagulation
Review status
Currently under review
Pending specialist review and validation.
This test measures the functional activity of coagulation factor XI in your blood plasma using a standardized dilution, which helps evaluate how well the intrinsic pathway of clotting is working. Factor XI, also called plasma thromboplastin antecedent, is a protein made in the liver that helps your body form stable blood clots after injury.
The assay reports activity in units per milliliter and reflects how effectively factor XI works compared with a normal plasma standard. It assesses how the protein performs in real time, which is different from a genetic test that looks for changes in the DNA sequence.
Clinicians order this test when there is a history of easy bruising, nosebleeds, heavy menstrual bleeding, bleeding after surgery or dental work, or when the activated partial thromboplastin time is prolonged. It helps diagnose inherited factor XI deficiency, sometimes called hemophilia C, and can identify acquired problems such as inhibitors or reduced production due to liver disease.
Results can guide planning before procedures, inform strategies to reduce bleeding risk, and in selected situations contribute to evaluating possible relationships between higher factor XI activity and clotting risk. Understanding your factor XI status helps your care team choose monitoring or treatment tailored to your needs.
If your factor XI activity is lower than expected, it may point to a deficiency. Some people have minimal bleeding in daily life yet experience problems after surgery or dental work. Your clinician may repeat testing, review your bleeding history, and order additional studies such as a mixing study, other factor levels, or tests for inhibitors to clarify the cause and guide care.
If your activity is higher than expected, your clinician will interpret it alongside your history, medications, and other laboratory results. Temporary changes can occur with illness or physiologic stress. An abnormal result does not by itself confirm a disorder. Your care team will discuss whether watchful waiting, preventive treatment before procedures, or referral to a specialist is appropriate.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
Underfilled or overfilled blue-top citrate tubes, clotted samples, hemolysis, or delayed processing can falsely alter factor XI activity. Proper tube fill, prompt centrifugation, and testing within recommended time frames are important.
Heparins and some direct oral anticoagulants can interfere with one-stage clotting assays, sometimes lowering apparent factor activity. Always tell your care team about all prescription and over-the-counter medications and supplements.
Factor XI is produced in the liver, so liver disease can reduce levels. Acute illness, inflammation, or stress can transiently influence clotting proteins, which may affect results.
Circulating inhibitors, including specific anti–factor XI antibodies or lupus anticoagulant, can interfere with the assay. Follow-up testing such as mixing studies helps distinguish deficiency from inhibition.
Physiologic changes in pregnancy and with estrogen-containing therapies can shift multiple clotting factors and may affect interpretation. Your clinician may use clinical context rather than isolated results to guide decisions.
Inherited factor XI deficiency varies in severity and can be more common in certain populations. Family history and background can help your clinician interpret results and decide on additional testing.
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