Inherited factor XIII deficiency affects 1 to 3 per million people worldwide. Researchers suspect that mild factor XIII deficiency, including the acquired form of the disorder, is underdiagnosed because many affected people never have a major episode of abnormal bleeding that would lead to a diagnosis.

Inherited factor XIII deficiency results from mutations in the F13A1 gene or, less commonly, the F13B gene. These genes provide instructions for making the two parts (subunits) of a protein called factor XIII. This protein plays a critical role in the coagulation cascade, which is a series of chemical reactions that forms blood clots in response to injury. After an injury, clots seal off blood vessels to stop bleeding and trigger blood vessel repair. Factor XIII acts at the end of the cascade to strengthen and stabilize newly formed clots, preventing further blood loss.

Mutations in the F13A1 or F13B gene significantly reduce the amount of functional factor XIII available to participate in blood clotting. In most people with the inherited form of the condition, factor XIII levels in the bloodstream are less than 5 percent of normal. A loss of this protein's activity weakens blood clots, preventing the clots from stopping blood loss effectively.

The acquired form of factor XIII deficiency results when the production of factor XIII is reduced or when the body uses factor XIII faster than cells can replace it. Acquired factor XIII deficiency is generally mild because levels of factor XIII in the bloodstream are 20 to 70 percent of normal; levels above 10 percent of normal are usually adequate to prevent spontaneous bleeding episodes.

Acquired factor XIII deficiency can be caused by disorders including an inflammatory disease of the liver called hepatitis, scarring of the liver (cirrhosis), inflammatory bowel disease, overwhelming bacterial infections (sepsis), and several types of cancer. Acquired factor XIII deficiency can also be caused by abnormal activation of the immune system, which produces specialized proteins called autoantibodies that attack and disable the factor XIII protein. The production of autoantibodies against factor XIII is sometimes associated with immune system diseases such as systemic lupus erythematosus and rheumatoid arthritis. In other cases, the trigger for autoantibody production is unknown.