Description

Evaluating Clotting Function and Bleeding Risk

What is it?

The Factor XI Activity Test measures the level of Factor XI, a key protein involved in blood clotting. This test helps identify Factor XI deficiency, a rare bleeding disorder that affects how well blood clots after injury or surgery.

Normal Range:

65–130 U/dL (or 65–130% activity)

Why is this test important?

Factor XI deficiency may not cause spontaneous bleeding, but it can lead to prolonged bleeding after surgery, trauma, or dental procedures—especially involving the mouth, nose, urinary tract, or menstrual cycle. It is more common in individuals of Ashkenazi Jewish descent.

Symptoms of Factor XI Deficiency may include:

  • Excessive or prolonged bleeding after surgery or injury
  • Frequent or unexplained nosebleeds
  • Easy bruising
  • Bleeding under the skin
  • Bleeding gums
  • Heavy or prolonged periods (menorrhagia) in women

Note: Some people with factor XI deficiency have mild or no symptoms.

How the test works:

A Factor XI activity assay is performed on a blood plasma sample. After adding calcium to the plasma, the test measures how long it takes to form a clot. The result is compared to a normal control sample to determine Factor XI activity.

Fasting not required.