Platform
Company
Coagulation
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Currently under review
Pending specialist review and validation.
Factor XII, also called Hageman factor, is a blood protein that helps start the contact pathway of clotting in the laboratory clotting cascade. The Factor XII 1:5 test measures how well this protein is working by assessing its functional activity in your plasma using a standardized dilution. It is typically performed with other coagulation studies to understand why a clotting time is prolonged or to check for a deficiency in contact factors.
Unlike many other clotting factor deficiencies, low Factor XII activity usually does not cause bleeding. The result mainly helps your care team interpret other tests, especially the activated partial thromboplastin time (aPTT), and to distinguish inherited from acquired causes of an abnormal result.
Your clinician may order this test when the aPTT is unexpectedly prolonged, when there is a family history of a contact factor deficiency, or as part of a workup for possible clotting system abnormalities. Finding a low Factor XII activity can point to a congenital deficiency or to interference from medications or antibodies, which guides next steps and prevents unnecessary procedures.
Although Factor XII deficiency typically does not lead to abnormal bleeding, it can complicate the interpretation of other clotting tests and has been studied for links with thrombosis. Knowing your Factor XII activity helps tailor your evaluation, avoid misdiagnosis, and decide whether additional testing or specialist referral is needed.
If your activity is lower than expected, your clinician may consider inherited deficiency, the presence of an inhibitor, or the effect of anticoagulant medications. Repeat testing, a mixing study, or checking for drug interference can help confirm the cause. If you take blood thinners or have an antiphospholipid antibody, results may appear lower than they truly are.
Higher activity values are usually not clinically significant on their own. Your care team will interpret this result together with your history, medications, and other labs. If results are unexpected, you may be asked to repeat the test, ensure proper sample collection, or see a hematology specialist for guidance.
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.
Underfilling the citrate tube, prolonged tourniquet time, delayed centrifugation, or heparin contamination can falsely lower factor activity. Proper fill level, prompt processing, and avoiding line draws through heparinized catheters help ensure accurate results.
Unfractionated heparin, low molecular weight heparin, direct thrombin inhibitors, and direct factor Xa inhibitors can prolong clot-based assays and make Factor XII activity appear reduced. Tell your clinician about all blood thinners before testing.
Antiphospholipid antibodies and specific factor inhibitors can interfere with phospholipid-dependent assays, mimicking a deficiency. Mixing studies and alternative methods may be needed to clarify true Factor XII activity.
Pregnancy, estrogen therapy, and acute illness or inflammation can change contact factor levels and assay behavior. Your clinician may time testing or interpret results in the context of these conditions.
Newborns naturally have lower levels of several contact factors, and liver disease can affect production of coagulation proteins. Age-appropriate interpretation and assessment of liver health may be important.
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