Overview
Factor X is a crucial blood-clotting protein also known as the Stuart-Prower Factor. It plays a central role in the coagulation cascade because it sits at the point where both the intrinsic pathway and the extrinsic pathway join together. When Factor X becomes activated (Factor Xa), it triggers the final major steps of clot formation, leading to the production of thrombin and fibrin, which help create a stable blood clot.
The Factor X Activity Test measures the level or activity of Factor X in the blood. It is used to diagnose bleeding disorders, evaluate liver function, investigate vitamin K deficiency, and assess unusual clotting tendencies.
What is Factor X?
Factor X is a protein found in the bloodstream in an inactive form. When bleeding occurs, a series of clotting steps activates this protein into Factor Xa, one of the most important enzymes in coagulation. Factor Xa works with Factor V to create the prothrombinase complex, which converts prothrombin into thrombin.
Without adequate Factor X, the clotting cascade becomes weak or incomplete. Too much Factor X may increase the risk of developing abnormal blood clots.
Where is Factor X Produced in the Body?
Factor X is produced in the liver, where most clotting factors are made. Its production requires:
1. Vitamin K
A critical nutrient needed for the activation of several clotting factors, including Factor X.
2. Healthy Liver Function
Diseases that damage liver cells reduce the body’s ability to make Factor X.
Main Functions and Importance of Factor X
Factor X plays a central role in the clotting process:
1. Convergence Point of Both Clotting Pathways
Both the intrinsic and extrinsic pathways activate Factor X, making it a crucial “gateway” to final clot formation.
2. Formation of the Prothrombinase Complex
Activated Factor X (Factor Xa) combines with Factor V, calcium, and phospholipids to form the prothrombinase complex.
3. Converts Prothrombin into Thrombin
This complex converts Prothrombin (Factor II) into Thrombin, the enzyme that drives multiple steps of clot formation.
4. Formation of Fibrin
Thrombin converts Fibrinogen into Fibrin, forming the mesh-like structure of a stable clot.
5. Prevents Excessive Bleeding
Factor X is essential to form strong, stable clots that protect the body from blood loss.
Causes of Low Factor X Levels
Low Factor X levels can be inherited or acquired.
1. Inherited Factor X Deficiency
A rare genetic disorder causing low functional Factor X.
Symptoms may appear early in life.
2. Severe Liver Disease
Cirrhosis, hepatitis, or other liver conditions decrease clotting factor production.
3. Vitamin K Deficiency
Occurs due to:
- Poor diet
- Fat malabsorption
- Liver problems
- Long-term antibiotics
Vitamin K is required for Factor X activation.
4. Warfarin or Vitamin K Antagonist Medications
These drugs block vitamin K, lowering Factor X activity.
5. Disseminated Intravascular Coagulation (DIC)
A serious condition where clotting factors, including Factor X, are quickly consumed.
6. Massive Blood Transfusions
Dilutes clotting factor levels, leading to temporary deficiency.
Symptoms of Low Factor X Levels
Symptoms of low Factor X levels include:
- Easy bruising
- Frequent or prolonged nosebleeds
- Gum bleeding
- Heavy menstrual bleeding
- Blood in urine or stool
- Prolonged bleeding after injury, surgery, or dental procedures
- In severe deficiency:
- Bleeding into joints or muscles
- Internal bleeding
- Brain hemorrhage (rare but life-threatening)
Severity depends on how low the Factor X activity is.
Causes of High Factor X Levels
High Factor X levels are less commonly discussed but may occur in:
- Inflammation
- Pregnancy
- Oral contraceptive pills
- Hormone replacement therapy
- Obesity or metabolic syndrome
- Some cardiovascular conditions
Elevated Factor X may increase the risk of thrombosis.
Symptoms of High Factor X Levels
High Factor X usually does not cause symptoms directly but may increase clot risk.
Possible clotting symptoms include:
- Pain, redness, warmth, and swelling in the leg (Deep Vein Thrombosis – DVT)
- Sudden chest pain
- Shortness of breath (Pulmonary Embolism – PE)
- Sudden weakness or speech difficulty (Stroke)
- Severe chest pain (Heart attack)
These are medical emergencies.
Reference Ranges
Typical Factor X activity levels:
50%–150% of normal activity
Lower than 40–50% may result in bleeding symptoms.
Ranges may vary slightly by laboratory technique.
Sample Type
- Venous blood sample from an arm vein
- Collected in a Light Blue Top Tube
- Additive: Sodium citrate
- Reason: Prevents clotting so the laboratory can accurately measure Factor X activity
The sample is processed to separate plasma, where clotting factor tests are performed.
Test Preparation
- No fasting required
- Avoid strenuous activity before testing
- Inform your doctor about:
- Warfarin or other blood thinners
- Vitamin K supplements
- Oral contraceptives or hormone therapy
- Liver disease
- Malabsorption problems
- Follow medical advice if you are adjusting blood thinner dosage
When to Consult a Doctor
Seek medical attention if you have:
Bleeding Symptoms
- Frequent nosebleeds
- Excessive bleeding after injuries
- Blood in urine or stool
- Easy bruising
- Heavy menstrual bleeding
- Bleeding after dental or surgical procedures
Signs of Possible Clots
- Leg swelling and pain
- Sudden chest discomfort
- Shortness of breath
- Severe headache
- Sudden weakness or numbness
Seek emergency care if clot symptoms appear.
Important Word Explanations
- Factor X: Clotting protein where the intrinsic & extrinsic pathways converge
- Stuart-Prower Factor: Another name for Factor X
- Prothrombinase Complex: Factor Xa + Factor V complex that produces thrombin
- Thrombin: Key enzyme that forms fibrin for clot stability
- DIC: Dangerous condition causing overuse of clotting factors
- Vitamin K: Nutrient needed for clotting factor activation
- Sodium Citrate Tube: Tube used for collecting coagulation samples
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