Overview
Factor V is an important protein in the blood that plays a key role in helping blood to clot. It is also called Proaccelerin or Labile Factor. Without adequate Factor V, the clotting process becomes slow or ineffective, leading to excessive bleeding. On the other hand, abnormally high Factor V activity—especially due to genetic mutations—can increase the risk of abnormal blood clots forming inside the blood vessels.
The Factor V test checks either the quantity or function (activity) of Factor V in the blood. It is commonly used to diagnose bleeding disorders, clotting disorders, liver disease, and inherited conditions such as Factor V Leiden mutation.
What is Factor V?
Factor V is one of the key clotting factors in the coagulation cascade, a series of steps the body uses to form blood clots. When an injury occurs, the clotting system activates a chain of reactions leading to the formation of a stable clot. Factor V acts as a co-factor—it helps other factors in the cascade work efficiently to form thrombin, which then converts fibrinogen into fibrin (the main structural component of a clot).
A deficiency or malfunction of Factor V leads to prolonged bleeding, while increased Factor V activity—especially due to genetic mutation—may increase the risk of thrombosis (clots forming inside the body).
Where is Factor V Produced in the Body?
Factor V is produced mostly in the liver, which is responsible for making many clotting factors. A smaller amount is produced by megakaryocytes, the large bone marrow cells that eventually form platelets. These platelets store some Factor V and release it during clot formation to help stabilize the clot.
Because the liver is the primary production site, any disorder affecting liver function can reduce Factor V levels.
Main Functions and Importance of Factor V
Factor V plays a central role in the clotting process:
1. Helps activate Prothrombin
Factor V helps convert prothrombin (Factor II) into thrombin, one of the most important enzymes in the clotting pathway.
2. Essential for Fibrin Formation
Thrombin converts fibrinogen into fibrin, forming a net-like structure that seals the injured area.
3. Works as a Co-factor
Factor V works with Factor X to create the prothrombinase complex, which speeds up clot formation.
4. Vital for controlled clotting
Balanced Factor V levels ensure:
- Bleeding stops effectively
- Clots do not form unnecessarily
Because of this, both low and high Factor V can be medically significant.
Causes of Low Factor V Levels
Low Factor V is uncommon but can occur due to several reasons:
1. Inherited Factor V Deficiency (Parahemophilia / Owren’s Disease)
A rare genetic condition where the body does not produce enough Factor V.
2. Liver Disease
Conditions like cirrhosis or hepatitis reduce production of clotting factors.
3. Disseminated Intravascular Coagulation (DIC)
A severe condition where clotting factors get consumed rapidly due to widespread clotting within the body.
4. Severe Infections
Some infections trigger clotting and breakdown of multiple clotting factors.
5. Massive Blood Transfusion
Dilutes clotting factors in the bloodstream.
6. Certain Medications
Drugs that affect clotting can lower Factor V activity.
Symptoms of Low Factor V Levels
Low Factor V leads to bleeding problems, such as:
- Easy bruising
- Prolonged nosebleeds
- Excessive bleeding after cuts or injuries
- Bleeding after surgery or dental procedures
- Blood in urine or stool
- Heavy menstrual bleeding (menorrhagia)
- Internal bleeding into muscles or joints (rare in FV deficiency but possible in severe cases)
Symptoms depend on how low the levels are.
Causes of High Factor V Levels
High Factor V can increase the risk of abnormal clot formation.
Common causes include:
1. Factor V Leiden Mutation
A genetic mutation that makes Factor V resistant to breakdown, increasing clot risk.
2. Pregnancy
Natural increase in clotting factors to reduce bleeding risk during childbirth.
3. Oral Contraceptives or Hormone Therapy
Estrogen increases clotting factor levels.
4. Inflammatory Conditions
Inflammation triggers the body to release more clotting factors.
5. Smoking / Obesity
Can increase clotting activity in the body.
Symptoms of High Factor V Levels
High Factor V alone usually does not cause symptoms, but when combined with mutations such as Factor V Leiden, it can lead to blood clots.
Symptoms may include:
- Swelling or pain in the legs (Deep Vein Thrombosis)
- Sudden chest pain
- Difficulty breathing (Pulmonary Embolism)
- Unexplained shortness of breath
- Pain or warmth in the leg veins
- Stroke-like symptoms in severe cases
These are medical emergencies.
Reference Ranges
Typical laboratory values:
Factor V Activity
50% – 200% of normal activity
Abnormal levels are interpreted based on symptoms and other clotting test results like PT, aPTT, and platelet count.
Sample Type
- Venous blood sample
- Collected in a Light Blue top tube
- Contains sodium citrate, which prevents the sample from clotting
- Plasma is used for Factor V activity or antigen measurement
Test Preparation
- No fasting required
- Avoid heavy exercise 24 hours before the test
- Inform your doctor about:
- Blood thinners
- Hormone therapy
- Pregnancy
- Recent surgeries
- Family history of clotting disorders
- Do not take any vitamin K supplements without informing your doctor
When to Consult a Doctor
Seek medical attention if you experience:
Bleeding-related symptoms
- Frequent nosebleeds
- Easy bruising
- Excessive bleeding after cuts
- Heavy menstrual bleeding
- Bleeding after dental work
Clotting-related symptoms
- Painful swelling in legs
- Sudden chest pain
- Difficulty breathing
- Severe abdominal pain
- Sudden numbness or weakness (possible stroke)
Seek emergency care if symptoms are severe.
Important Word Explanations
- Factor V: A clotting protein needed for normal blood coagulation
- Proaccelerin: Another name for Factor V
- Factor V Leiden: A genetic mutation increasing clot risk
- Thrombin: Enzyme that converts fibrinogen to fibrin
- DIC: A severe condition where clotting factors are overused
- Sodium Citrate Tube: A tube used for collecting coagulation test samples
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