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Factor XII deficiency is an inherited disorder that affects a protein (factor XII) involved in blood clotting.

When you bleed, the body launches a series of reactions that help the blood clot. This is called the coagulation cascade. The process involves special proteins called coagulation factors. (Factor XII is a coagulation factor in this series of reactions.)

Each factor has a reaction that triggers the next reaction. The final product of the coagulation cascade is the blood clot.

A lack of factor XII does not cause the affected person to bleed abnormally, but the blood takes longer than normal to clot in a test tube.

Factor XII deficiency is a rare inherited disorder.

There are usually no symptoms.

Factor XII deficiency is usually found when clotting tests are done for routine screening.

Tests may include:

• Factor XII assay
• Partial thromboplastin time (PTT)

Treatment is generally unnecessary.

The outcome is expected to be good without treatment.

There are usually no complications.

This condition is usually discovered by the health care provider, when prolonged clotting is noticed in the process of running other laboratory tests.

This is an inherited disorder. There is no known way to prevent it.

Kessler C. Hemorrhagic disorders: Coagulation factor deficiencies. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 180.

Updated by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and Yi-Bin Chen, MD, Leukemia/Bone Marrow Transplant Program, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.