Factor V deficiency, also known as Owren’s disease or parahemophilia, is a very rare blood clotting disorder that results in slow or prolonged blood clotting after an injury or surgery. Factor V (proaccelerin) is a protein made in the liver that helps convert prothrombin into thrombin, an important step in the blood clotting process. If you do not have enough factor V, or if it doesn’t work properly, your blood clots may be too weak to stop you from bleeding.
Factor V deficiency may occur at the same time as factor VIII deficiency, producing more severe blood clotting problems. The combined factor V and factor VIII deficiency is considered to be a separate disorder.
Factor V is one of about 13 clotting factors responsible for normal blood coagulation. To understand factor V deficiency, it helps to know how factor V functions in normal blood clotting. Blood clotting occurs in four stages:
- Vasoconstriction. When a blood vessel is cut, it immediately constricts to slow blood loss. It then releases cells into the blood stream telling the blood clotting factors to start the coagulation process.
- Formation of the Platelet Plug. Blood platelets collect at the site of the wound and begin sticking to the wound and to each other. This forms a soft platelet plug in the wound. This stage is called primary hemostasis.
- Formation of the fibrin plug. Once the platelets form a temporary plug, a complex chain reaction takes place among multiple blood clotting factors. Factor V appears about halfway through this chain of reactions and is responsible for converting prothrombin into thrombin. Thrombin triggers fibrinogen to produce fibrin, the material that makes up the final blood clot.
Fibrin is a stringy protein that wraps itself in and around the temporary soft clot, making it harder and more resistant. This new clot seals the broken blood vessel and creates a protective covering for tissue regeneration. This stage is called secondary hemostasis.
- Wound healing and destruction of the fibrin plug. After a few days, the fibrin clot starts to shrink, pulling the edges of the wound together to allow the damaged tissue to rebuild. As the underlying tissue is rebuilt, the fibrin clot dissolves.
If you have factor V deficiency, secondary hemostasis does not occur properly, resulting in prolonged bleeding.
Factor V deficiency may be inherited or acquired after birth. Hereditary factor V deficiency is extremely rare. It is caused by a recessive gene, which means that you have to inherit the gene from both of your parents in order to show symptoms. There are only 105 documented cases of inherited factor V deficiency in the world.
Acquired factor V deficiency may be caused by medications, underlying medical conditions, or an autoimmune reaction. Underlying conditions that might affect factor V include:
- disseminated intravascular coagulation (DIC) (a condition that causes clotting proteins to become over-active, leading to small blood clots and excessive bleeding)
- liver diseases, such as cirrhosis of the liver
- secondary fibrinolysis (when fibrin clots tend to break down)
- autoimmune diseases such as lupus
- spontaneous autoimmune reactions after surgery or childbirth
- certain types of cancer
Symptoms of factor V deficiency are generally very mild. Factor V levels can be as low as 10-20 percent of normal and your blood will still clot, although a bit more slowly.
In cases of severe factor V deficiency, symptoms may include:
Your doctor will diagnose you based on your medical history, any family history of bleeding problems, and laboratory tests. Common lab tests for factor V include the following:
Factor assays measure the performance of specific clotting factors to identify missing or poorly performing factors.
Factor V assay measures how much factor V you have and how well it works.
Prothrombin time (PT) measures clotting time affected by factors I, II, V, VII, and X.
Partial prothrombin time (PTT) measures clotting time affected by factors VIII, IX, XI, XII and von Willebrand factors.
Inhibitor tests determine if your body’s own immune system is suppressing your blood clotting factors.
Other tests will likely be ordered to identify any underlying conditions resulting in factor V deficiency.
Since factor V deficiency is generally mild, treatment is mostly precautionary. Before surgery or dental procedures, your doctor may recommend you use desmopressin (DDAVP). DDAVP is a nasal spray that temporarily boosts your factor levels. In the event of a severe bleeding episode, you may be given infusions of fresh frozen plasma (FFP) and blood platelets to replace your missing blood clotting factor.
Factor V deficiency is relatively mild compared to other blood clotting disorders. Most sufferers bleed for slightly longer than those without factor V deficiency, but can live very normal lives.