Factor V deficiency is also known as Owren’s disease or parahemophilia. It’s a rare bleeding disorder that results in poor clotting after an injury or surgery. Factor V deficiency shouldn’t be confused with factor V Leiden mutation, a much more common condition that causes excessive blood clotting.
Factor V, or proaccelerin, is a protein made in your liver that helps convert prothrombin into thrombin. This is an important step in the blood clotting process. If you don’t have enough factor V or if it doesn’t work properly, your blood may not clot effectively enough to stop you from bleeding. There are different levels of severity of factor V deficiency based on how little or how much factor V is available to the body.
Factor V deficiency may also occur at the same time as factor VIII deficiency, producing more severe bleeding problems. The combination of factor V and factor VIII deficiencies is considered to be a separate disorder.
Factor V is one of about 13 clotting factors responsible for normal blood coagulation, or clotting. Blood clotting occurs in stages:
- When one of your blood vessels is cut, it immediately constricts, or narrows, to slow blood loss. This is called vasoconstriction. Chemical messages are sent into the bloodstream to signal the body to release blood clotting factors and start the coagulation process.
- Blood platelets collect at the site of the wound and begin sticking to the wound and to each other. These form a soft platelet plug in your wound. This stage is called primary hemostasis.
- 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 converts prothrombin into thrombin.
- Thrombin triggers fibrinogen to produce fibrin. Fibrin is the material that makes up the final blood clot. It’s a stringy protein that wraps itself in and around the temporary soft clot, which makes the clot harder. This new clot seals the broken blood vessel and creates a protective covering for tissue regeneration. This stage is called secondary hemostasis.
- 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.
Secondary hemostasis doesn’t occur properly if you have factor V deficiency. This results in prolonged bleeding.
Factor V deficiency may be inherited or acquired after birth.
Hereditary factor V deficiency is rare. It’s caused by a recessive gene, which means that you have to inherit the gene from both of your parents in order to show symptoms. This form occurs in about 1 in 1 million people.
Acquired factor V deficiency may be caused by certain medications, underlying medical conditions, or an autoimmune reaction.
Conditions that might affect factor V include:
- disseminated intravascular coagulation (DIC), which is a condition that causes small blood clots and excessive bleeding due to overactive clotting proteins
- liver diseases, such as cirrhosis
- secondary fibrinolysis, which occurs when clots tend to break down due to medications or health conditions
- autoimmune diseases, such as lupus
- spontaneous autoimmune reactions after surgery or childbirth
- certain types of cancer
The symptoms of factor V deficiency vary depending on the amount of factor V available to the body. The levels necessary to cause symptoms depend upon the individual. A certain level that may cause bleeding in one person may not clause bleeding in another person.
In cases of severe factor V deficiency, the symptoms often include:
Many people who have this condition received their diagnosis when doctors ran blood coagulation tests before surgery. 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.
- Activated partial prothrombin time (aPTT) measures clotting time affected by factors I, II, V, VIII, IX, X, XI, XII, and von Willebrand factors.
- Inhibitor tests determine if your immune system is suppressing your blood clotting factors.
Your doctor will likely order other tests to identify any underlying conditions resulting in factor V deficiency.
Factor V deficiency is treated with infusions of fresh frozen plasma (FFP) and blood platelets. These infusions are typically needed only after surgery or a bleeding episode.
Factor V deficiency is relatively manageable compared to other bleeding disorders. Many people can tolerate low levels of factor V without symptoms. People who have this condition often need treatment only after surgery or a very serious injury. These people usually have normal lives and only bleed a little bit longer than people who have blood that coagulates normally.