Platform
Company
Coagulation
Review status
Currently under review
Pending specialist review and validation.
This test measures the activity of coagulation Factor XII in your plasma. Factor XII, also called Hageman factor, helps start the contact activation pathway of blood clotting and also interacts with inflammation and kallikrein-kinin systems. The result reflects how well the factor functions compared with a normal control.
Your blood is collected in a citrate tube and analyzed with a functional assay that uses a defined dilution. The test assesses activity, not just the amount of the protein, and is typically interpreted together with other clotting studies such as the activated partial thromboplastin time and, when needed, mixing studies or tests of related factors.
Doctors order this test to evaluate a prolonged activated partial thromboplastin time, to look for inherited or acquired Factor XII deficiency, or to clarify unexpected results before procedures. Unlike deficiencies of many other clotting factors, low Factor XII activity usually does not cause bleeding, so identifying it can prevent unnecessary worry and guide appropriate care.
Results can also point toward other explanations for abnormal clotting tests, including medication effects or the presence of inhibitors that interfere with assays. Some research links abnormal Factor XII activity to certain clotting or inflammation conditions, but these associations are complex and are best interpreted alongside your history, exam, and other laboratory findings.
A low activity result may be due to a congenital deficiency, an acquired decrease from illness, or an effect of anticoagulant medicines that interfere with the assay. If your activated partial thromboplastin time is prolonged but you do not have bleeding symptoms, a low Factor XII level can explain the laboratory finding without indicating a bleeding disorder.
If results are unexpected, your clinician may repeat the test, review how the sample was collected, or order companion studies such as mixing tests or assays of other contact factors. Tell your care team about all medicines and supplements. If you are taking heparin or direct oral anticoagulants, the blood draw may be timed or testing deferred to reduce interference and improve accuracy.
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 blue-top citrate tube alters the blood-to-anticoagulant ratio and can artifactually lower measured activity. Proper fill and gentle mixing help ensure reliable results.
Heparin and some direct oral anticoagulants can interfere with clot-based assays, making Factor XII activity appear lower than it really is. Your team may adjust timing or use heparin-neutralizing approaches.
Delays in centrifugation, improper storage, or repeated freeze-thaw can activate or degrade proteins and skew results. Prompt processing and correct temperature control are important.
Phospholipid-dependent inhibitors and nonspecific antibodies can prolong clotting tests and confound activity assays. Additional studies, such as mixing tests, may be needed to clarify the picture.
Acute illness, inflammation, liver disease, and hormonal therapies like estrogen can change contact pathway proteins. Your clinical context helps determine whether a change is meaningful.
Congenital Factor XII deficiency is often discovered during evaluation of a prolonged aPTT and typically does not cause bleeding. Family testing may be discussed if a hereditary pattern is suspected.
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