Overview
Factor II, also known as Prothrombin, is one of the most essential proteins in the blood-clotting system. When an injury occurs, prothrombin is converted into thrombin, a powerful enzyme that helps form a stable blood clot. Without adequate levels of Factor II, bleeding can become excessive or prolonged. On the other hand, too much prothrombin can increase the risk of abnormal clot formation inside the body.
The Factor II – Prothrombin Activity Test measures how much prothrombin is present in the blood and how well it functions. This test is used to investigate unexplained bleeding, clotting disorders, liver problems, vitamin K deficiency, and the effects of medications such as warfarin.
What is Factor II – Prothrombin Activity Test?
The Factor II test measures either:
- Prothrombin activity (how well it works), or
- Prothrombin antigen (how much is present)
This helps doctors identify whether the body is producing enough prothrombin and whether the coagulation system is working normally.
Doctors order this test when patients experience:
- Frequent bleeding or bruising
- Prolonged bleeding after injury
- Unexplained blood clots
- Abnormal coagulation test results (especially prolonged PT)
- Suspected liver disease
- Vitamin K deficiency
- Monitoring of warfarin therapy
This test is essential for diagnosing both bleeding disorders and clotting disorders.
Where is Factor II Produced in the Body?
Factor II is produced in the liver, which manufactures most of the body’s clotting factors.
Its production requires:
1. Vitamin K
A fat-soluble vitamin necessary to activate prothrombin.
Without vitamin K, the liver cannot produce functional Factor II.
2. Healthy Liver Cells
Any disease that affects liver function can reduce Factor II production, leading to bleeding problems.
Main Functions and Importance of Factor II
Factor II plays multiple key roles in the coagulation process:
1. Converts Prothrombin to Thrombin
During the clotting process, Factor II is converted into thrombin, which is essential for advancing the clotting cascade.
2. Thrombin Creates Fibrin
Thrombin converts fibrinogen to fibrin, creating the net-like structure that stabilizes blood clots.
3. Activates Other Clotting Factors
Thrombin activates several other factors, including:
- Factor V
- Factor VII
- Factor VIII
- Factor XIII
This amplifies clot formation and stabilizes the clot.
4. Activates Platelets
Thrombin triggers platelets to clump together, helping seal the injury more effectively.
5. Essential for Stopping Bleeding
Adequate levels prevent excessive bleeding and ensure wounds heal properly.
Causes of Low Factor II Levels
Low prothrombin levels lead to impaired clot formation.
Common causes include:
1. Inherited Prothrombin Deficiency
A rare genetic disorder where the body produces insufficient Factor II.
2. Liver Disease
Conditions like hepatitis, cirrhosis, or liver failure impair clotting factor production.
3. Vitamin K Deficiency
May occur due to:
- Poor diet
- Fat malabsorption
- Long-term antibiotic use
- Newborn vitamin K deficiency
4. Warfarin Use
Warfarin blocks vitamin K, reducing prothrombin production.
5. Disseminated Intravascular Coagulation (DIC)
Clotting factors are rapidly consumed due to widespread clotting.
6. Massive Blood Transfusion
Dilutes clotting factor levels.
Symptoms of Low Factor II Levels
Low Factor II causes bleeding symptoms, including:
- Easy bruising
- Frequent nosebleeds
- Gum bleeding
- Heavy menstrual bleeding
- Prolonged bleeding after cuts or surgery
- Blood in urine or stool
- Internal bleeding (rare but severe)
- Brain bleeding or abdominal bleeding (critical cases)
Severity depends on how low the levels are.
Causes of High Factor II Levels
Excess Factor II increases clot formation risk.
Common causes include:
1. Prothrombin G20210A Mutation
A genetic mutation causing increased prothrombin production.
2. Pregnancy
Natural increase in clotting factors to protect from bleeding during childbirth.
3. Oral Contraceptives or Hormone Therapy
Estrogen increases clotting factor activity.
4. Obesity and Metabolic Syndrome
Associated with hypercoagulable states.
5. Inflammation and Cardiovascular Disease
Some inflammatory or metabolic conditions elevate Factor II levels.
Symptoms of High Factor II Levels
High Factor II usually does not cause direct symptoms, but increases the risk of thrombosis.
Possible signs include:
- Swelling, redness, or pain in legs (Deep Vein Thrombosis – DVT)
- Sudden chest pain
- Breathlessness (Pulmonary Embolism – PE)
- Sudden numbness or weakness (Stroke)
- Chest pain or pressure (Heart attack)
These conditions are medical emergencies.
Reference Ranges
Typical Factor II activity:
50% – 150% of normal
Range may vary depending on the laboratory and testing method.
Levels below 50% often cause bleeding symptoms.
Sample Type
- Venous blood sample collected from the arm
- Collected in a Light Blue Top Tube
- Additive: Sodium Citrate
- Reason: Prevents clotting inside the tube so the lab can measure clotting factor activity accurately
Test Preparation
- No fasting required
- Avoid alcohol 24 hours before the test
- Inform your doctor if you are taking:
- Warfarin
- Blood thinners
- Vitamin K supplements
- Hormonal medications
- Tell your doctor if you have:
- Liver disease
- Malabsorption issues
- Recent infection
- Follow instructions if stopping or adjusting blood thinners
When to Consult a Doctor
Seek medical help if you have:
Bleeding Symptoms
- Heavy or prolonged bleeding
- Frequent nosebleeds
- Blood in urine or stool
- Easy bruising
- Bleeding after dental procedures
Clotting Symptoms
- Leg swelling and pain
- Sudden breathlessness
- Chest pain
- Severe headache
- Vision changes
- Symptoms of stroke
Seek emergency care if clotting symptoms appear suddenly.
Important Word Explanations
- Prothrombin (Factor II): A clotting protein needed to produce thrombin
- Thrombin: Enzyme that forms fibrin for stable clots
- Vitamin K: Nutrient required for clotting factor activation
- DIC: A condition causing overuse of clotting factors
- Warfarin: Blood thinner that lowers Factor II levels
- Antigen vs Activity: Amount of protein vs how well it functions
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