Antithrombin analysis causes results and risks

The antithrombin test is one of the most important blood coagulation tests, especially for people who suffer from recurrent blood clots or have a family history of thrombosis.Antithrombin is a natural protein in the body, and its primary function is to prevent clot formation and maintain the balance of the blood coagulation process within blood vessels. Any imbalance in its levels, whether increased or decreased, can expose a person to serious complications such as venous thrombosis or excessive bleeding.

For this reason, doctors request the antithrombin test in specific situations to:

Determine the cause of blood clots
Evaluate the effectiveness of anticoagulant therapy
Diagnose inherited or acquired coagulation disorders

In this Daleeli Medical article, you will learn in detail about the uses of the antithrombin test, reasons for performing it, normal values, interpretation of results, potential risks, and clear answers to the most frequently asked questions.

What is the Antithrombin Test?
The antithrombin test is an important blood test that measures the level or activity of the antithrombin protein in the body.
This protein plays a key role in preventing excessive blood clot formation and maintaining the balance of the coagulation process in blood vessels. Any abnormality in its levels can increase the risk of blood clots or bleeding.

Why Does the Doctor Request an Antithrombin Test?
Doctors order this test in certain situations, including:

Recurrent blood clots without a clear cause
Blood clots occurring at a young age
Poor response to heparin therapy
Family history of blood clots
Suspected inherited or acquired clotting disorders

The test helps determine the underlying cause of blood clots and guide an appropriate treatment plan.

Is the Antithrombin Test a Routine Test?
No, the antithrombin test is not routine. It is only requested when there is suspicion of blood clotting disorders or antithrombin deficiency, not as a regular screening test.

Does the Antithrombin Test Require Fasting?
In most cases:

Fasting is not required
However, it is always best to follow the instructions of the doctor or laboratory
Some special cases may require additional instructions depending on the health condition

Does Pregnancy Affect the Antithrombin Test Result?
Yes, during pregnancy:

A slight, normal decrease in antithrombin levels may occur
Therefore, results should be interpreted carefully
Follow-up with a specialist is recommended for accurate evaluation

Does Heparin Affect the Antithrombin Test?
Yes, heparin affects the results because it works through antithrombin.

It is preferable to perform the test before starting heparin therapy
Or after stopping it for a period determined by the doctor
This ensures accurate results

What is the Difference Between Antithrombin Activity and Antithrombin Level Tests?
There are two types of antithrombin tests, each with a different purpose:

Activity test: Measures how effectively antithrombin prevents clot formation
Level (quantity) test: Measures the amount of antithrombin protein in the blood

Doctors often use both tests together to determine whether a deficiency is due to a quantitative lack or a functional defect.

Does Low Antithrombin Mean You Will Have a Blood Clot?
Not necessarily, but:

Low antithrombin increases the risk of clot formation
Especially if other risk factors are present, such as pregnancy, surgery, immobility, or family history
Medical follow-up is essential even without a clot

Is Antithrombin Deficiency Genetic?
Yes, antithrombin deficiency can be:

Inherited (congenital): present from birth
Acquired: due to liver disease, acute clotting events, or certain medications

Differentiating between the two types is important for determining the monitoring and treatment plan.

Can Antithrombin Deficiency Be Treated?
There is no definitive cure for inherited deficiency, but the condition can be managed by:

Preventing blood clots
Using anticoagulants when needed
Regular medical follow-up
Avoiding risk factors such as immobility and smoking

When Might Antithrombin Test Results Be Inaccurate?
Results may be inaccurate if the test is performed during:

Acute clot formation
Heparin therapy
Severe infections
Recent major surgery

In such cases, the doctor may request a repeat test after the condition stabilizes.

Do Children Need an Antithrombin Test?
Rarely, but it may be requested in children in specific situations, such as:

Unexplained blood clots
Strong family history of inherited clotting disorders

The test should be performed under medical supervision.

Does the Antithrombin Test Detect All Causes of Blood Clots?
No, it only detects one cause of clotting disorders.
It is often requested along with other tests such as:

Protein C
Protein S
Factor V Leiden

Together, these tests provide a more comprehensive picture of clotting risks.

Is High Antithrombin Dangerous?
In most cases, elevated antithrombin is not considered dangerous and usually has no significant medical implication.
Medical concern is usually focused on low antithrombin because it increases the risk of clot formation.

Can the Antithrombin Test Be Repeated?
Yes, repeating the test is common to:

Confirm accuracy of results
If performed during an acute clot
Or during use of medications that may affect results

Repeating the test helps the doctor make a more precise diagnosis.

Does Dehydration Affect Antithrombin Test Results?
Severe dehydration may indirectly affect blood protein concentrations.
It is recommended to drink adequate water before the test.

Are Antithrombin Levels Different Between Men and Women?
Reference values are very similar between men and women.

During pregnancy, there may be a slight temporary decrease
Results should be interpreted carefully in this case

Can Antithrombin Deficiency Cause Miscarriage?
Low antithrombin may increase the risk of:

Blood clots in the placenta
This may affect pregnancy in some cases

Regular medical follow-up during pregnancy is important.

Does Age Affect Antithrombin Test Results?
Yes:

Newborns naturally have lower antithrombin levels.
Levels gradually increase with age until reaching the normal adult range.

Can the Test Be Done During Menstruation?
Yes, menstruation does not directly affect antithrombin test results, and the test can be performed at any time.

Does Diet Affect the Test Result?
Food itself does not directly affect the test, but:

Poor nutrition
Liver disease
can affect antithrombin levels in the blood.

Is the Antithrombin Test Painful?
The test is almost painless:

It involves only a small needle prick.
It usually does not cause complications.

Are Special Preparations Needed?
No complex preparations are needed, but it is important to:

Inform the doctor about all medications, especially anticoagulants like heparin.

Is Low Antithrombin an Emergency?
If the decrease is:

Severe
Accompanied by a clot or serious symptoms
it may require urgent medical attention.

Can Antithrombin Deficiency Complications Be Prevented?
Yes, risks can be reduced by:

Regular medical follow-up
Avoiding prolonged sitting or bed rest
Following preventive treatment if prescribed

Can Test Results Be Normal Despite a Blood Clot?
Yes, some clots occur due to factors other than antithrombin deficiency.

Diagnosis should not rely solely on this test.
Usually, other coagulation tests are requested to determine the cause accurately.

When Might Genetic Testing Be Requested Alongside Antithrombin Testing?
Genetic tests may be requested in cases such as:

Recurrent unexplained blood clots
Strong family history of clots
Clots occurring at a young age

These tests help diagnose inherited clotting disorders and guide follow-up and prevention strategies.

Types of Antithrombin Tests

Antithrombin testing has two main types that complement each other for accurate diagnosis:

1️⃣ Antithrombin Activity Test

Measures how efficiently antithrombin prevents clot formation.
Indicates whether the protein is functioning properly.

When is it Used?

Recurrent clots
Poor or no response to heparin therapy
Most commonly requested by doctors as the first step

Interpretation:

Low activity → Functional defect or deficiency
Normal activity → Usually indicates proper function

2️⃣ Antithrombin Antigen (Level) Test

Measures the actual amount of antithrombin in the blood without assessing functionality.

When is it Used?

After an abnormal activity test
Determines the type of deficiency:
- Quantity deficiency
- Functional defect

This distinction helps choose the correct follow-up and treatment plan.

Uses of Antithrombin Testing

1️⃣ Diagnosing Inherited Clotting Disorders

Some people are born with antithrombin deficiency, increasing the risk of deep vein or pulmonary clots.
Deficiency may be partial or complete and often causes recurrent clots from adolescence or young adulthood.

2️⃣ Diagnosing Acquired Antithrombin Deficiency

Caused by liver or kidney disease, certain medications, or chronic medical conditions.
Examples: liver failure or nephrotic syndrome (protein loss in urine).

3️⃣ Evaluating Causes of Recurrent Clots

Helps determine if clots are due to antithrombin deficiency.
Especially important for individuals with a family history or pregnant women who experienced clots.

4️⃣ Monitoring Heparin Therapy

Heparin requires antithrombin to be effective.
Testing evaluates the body’s response and guides dose adjustment.

5️⃣ Assessing Clot Risk Before Surgery or During Pregnancy

Major surgeries and pregnancy increase clot risk.
The test helps doctors take preventive measures, including anticoagulant use if necessary.

6️⃣ Monitoring Chronic Diseases

Liver disease decreases protein production, affecting antithrombin levels.
Kidney disease causes protein loss in urine.
Regular monitoring prevents clotting complications.

7️⃣ Determining Type of Defect in Other Clotting Disorders

Deficiency may be partial or functional, guiding appropriate treatment.
Often combined with other tests like fibrinogen, prothrombin, and platelet counts for a comprehensive coagulation assessment.

How the Test is Performed

1️⃣ Preparation

Inform the doctor about medications (e.g., heparin, warfarin).
Avoid extreme physical or psychological stress.
Fasting is usually not required but follow doctor’s instructions.
Mention chronic diseases like liver/kidney disease or previous clots.

2️⃣ Blood Draw Preparation

Select a suitable vein (usually in the arm).
Clean the skin with alcohol.
Technician wears sterile gloves.

3️⃣ Blood Collection

Small needle used to draw 2–5 mL of blood into a tube containing anticoagulant (EDTA or citrate).
Sit still and avoid moving the arm.

4️⃣ Laboratory Processing

Gently mix the tube to combine anticoagulant with blood.
Send immediately to chemistry or coagulation lab.

5️⃣ Laboratory Analysis

Special devices measure antithrombin activity or level.
Results expressed as Activity % (most common) or Antigen level.
Compared to reference values to detect deficiency or functional defect.

Risks of the Test

1️⃣ Risks Related to Blood Draw

Bruising or minor bleeding: usually resolves in days. Press on the site to reduce bruising.
Pain or prick at needle site: normal and temporary.
Dizziness or fainting: common with needle fear or insufficient food. Sit during the draw and drink water afterward.
Rare infection: minimized by sterilization and proper equipment.

2️⃣ Risks Related to Results

Inaccurate results may lead to misdiagnosis or inappropriate treatment.
To avoid this: follow instructions, inform the doctor about medications and conditions, repeat test if needed.

3️⃣ Risks for Specific Groups

People with bleeding disorders: higher risk of bleeding.
Immunocompromised individuals: extra caution to avoid contamination.

4️⃣ Tips to Minimize Risks

Sit still and avoid moving the arm.
Press on the puncture site after the draw.
Drink water afterward.
Inform the doctor of bleeding disorders or immune deficiencies.
Ensure lab uses clean, sterile equipment.

Antithrombin Test Results

Measures antithrombin level or activity, responsible for preventing clots and maintaining coagulation balance.
Expressed as Activity % or sometimes as quantitative level (mg/dL or g/L).

1️⃣ Normal Values

Activity: 80% – 120%
Quantitative level: ~20–40 mg/dL (may vary by lab)

2️⃣ Interpretation of Results

Result	Possible Meaning	Notes
Normal	Normal activity, low risk of clots	No additional follow-up if asymptomatic
Low activity/level (<80%)	Antithrombin deficiency, increased clot risk	May be inherited or acquired (liver/kidney disease, medications)
High activity/level (>120%)	Rare, usually clinically insignificant	May be temporary after certain conditions or medications

3️⃣ Causes of Low Antithrombin

Inherited deficiency (partial or complete)
Liver disease (reduced production)
Kidney disease (protein loss in urine)
Certain medications (e.g., long-term heparin, anticoagulants affecting activity measurement)
Pregnancy or acute infections (temporary decrease)

4️⃣ Causes of High Antithrombin

Rare, usually temporary, and clinically insignificant
Certain medications (bone marrow stimulants or some anticoagulants)
Pregnancy or physiological changes (slight temporary increase)
Compensation after prior temporary decrease (disease or protein loss)
Lab/technical issues (delayed processing, equipment differences); repeat testing or interpretation with a doctor is recommended