Factor X assay

Factor X Assay

Factor X assay is a medical laboratory test used to detect deficiencies or elevated levels of factor X, one of the serine proteases involved in the coagulation cascade. Abnormal Factor X results may indicate bleeding disorders, such as hemophilia, or other conditions affecting clotting of the blood.


No special preparation is necessary for a Factor X assay. Some laboratories may request that the patient refrain from taking anti-coagulants, such as aspirin, prior to testing, as such medications can alter results.


Factor X assay generally involves the patient providing a small volume of blood. The blood is processed in a laboratory, which prepares it and measures the levels of Factor X. The laboratory report includes the patient's Factor X levels, which is presented as a numerical figure and results indicate if levels are normal, low, or high.


  • Factor X Activity Assay
  • Factor X Antigen Assay


The risks associated with a Factor X assay are minimal. Minor discomfort and bruising may occur at the site of the blood draw, but this should resolve quickly. Uncommon risks include severe pain or infection from the site of the blood draw due to improper technique.

Why It's Done

The Factor X assay is performed to help diagnose and manage a bleeding disorder. It may also be done to determine if a patient’s clotting factors are slowed, in the event of blood clots or if they are taking a blood-thining medication such as warfarin (Coumadin). Factor X is also sometimes checked to rule out other medical conditions that could interfere with the clotting process.

When to Do It

Your healthcare provider may request a Factor X assay if they suspect you may have a bleeding disorder, such as hemophilia, or if you are experiencing prolonged or excessive bleeding. The test may also be done if you have a history of blood clots, or if you are taking a blood-thinning medication.