What is Alpha-1 Antitrypsin (AAT)?
The Alpha-1 Antitrypsin (AAT) Test is a blood test that measures the level of alpha-1 antitrypsin, a protective protein made by the liver.
This protein acts as a natural shield for the lungs, preventing damage from harmful enzymes such as neutrophil elastase, which can destroy lung tissue during inflammation.
Doctors use the AAT test primarily to:
- Diagnose Alpha-1 Antitrypsin Deficiency (AATD) — a genetic disorder that can cause lung diseases (emphysema, COPD) or liver damage
- Evaluate the cause of unexplained liver disease, especially in infants or young adults
- Investigate early-onset lung conditions in non-smokers
Where is Alpha-1 Antitrypsin Produced in the Body?
AAT is produced mainly in the liver and released into the bloodstream.
Once in the blood, it travels to the lungs and other tissues, where it helps control inflammation and protect cells from enzyme-related damage.
If the liver produces a defective form of AAT (due to genetic mutation), it can accumulate inside liver cells, leading to liver injury, while reduced AAT in blood increases the risk of lung damage.
Main Functions and Importance of Alpha-1 Antitrypsin
AAT has several crucial protective roles in the body:
1. Protects the Lungs
AAT neutralizes neutrophil elastase, an enzyme released by white blood cells that helps fight infections but can destroy lung tissue if not controlled.
2. Prevents Emphysema and COPD
Adequate AAT levels help prevent lung destruction and maintain elasticity, lowering the risk of chronic obstructive pulmonary disease (COPD) and emphysema.
3. Protects the Liver
By preventing enzyme accumulation and inflammation, AAT reduces the risk of liver fibrosis, cirrhosis, and hepatitis.
4. Supports Inflammation Control
AAT acts as an anti-inflammatory agent, regulating enzyme activity during infections or injury.
Causes of Low AAT Levels
Low levels of AAT can be inherited or acquired.
The most common reason is Alpha-1 Antitrypsin Deficiency (AATD) — a genetic disorder caused by mutations in the SERPINA1 gene.
Common causes:
- Genetic deficiency (AATD) – inherited in an autosomal co-dominant manner
- Liver disease – reduces AAT synthesis
- Severe malnutrition – low protein production overall
- Nephrotic syndrome – loss of protein through urine
Symptoms of Low AAT Levels
Low AAT levels usually cause lung or liver-related symptoms, which can appear in adulthood or infancy.
Lung Symptoms:
- Shortness of breath, especially during exertion
- Chronic cough with mucus
- Wheezing or asthma-like symptoms
- Frequent chest infections
- Early-onset COPD or emphysema (even in non-smokers)
Liver Symptoms:
- Jaundice (yellowing of skin or eyes)
- Fatigue and weakness
- Swollen abdomen due to fluid accumulation (ascites)
- Enlarged liver or spleen
- Elevated liver enzymes in blood tests
In Infants:
- Neonatal hepatitis
- Prolonged jaundice
- Poor feeding or growth failure
Causes of High AAT Levels
High levels of AAT are usually temporary and occur as part of the body’s acute phase response to inflammation or infection.
Common causes include:
- Acute infections (bacterial or viral)
- Inflammation (such as arthritis or autoimmune disease)
- Pregnancy (natural increase in plasma proteins)
- Cancer (especially of the liver or lung)
- Stress or trauma
Symptoms of High AAT Levels
High AAT alone usually does not cause symptoms.
Instead, it reflects an underlying inflammatory or disease process.
In such cases, doctors will look for the primary condition causing the elevation.
Reference Ranges
The normal range of Alpha-1 Antitrypsin in blood can vary slightly among laboratories, but generally:
| Category | Normal Range |
|---|---|
| Adults | 90 – 200 mg/dL |
| Mild Deficiency | 80 – 90 mg/dL |
| Severe Deficiency (AATD) | < 80 mg/dL |
⚠️ A level below 80 mg/dL strongly suggests Alpha-1 Antitrypsin Deficiency.
Sample Type and Handling
| Parameter | Details |
|---|---|
| Sample Type | Serum |
| Tube Type | Plain Red-top or Serum Separator Tube (SST) |
| Fasting Required | Not necessary |
| Special Instructions | Avoid testing during acute infections for more accurate results. |
How the AAT Test is Performed
- A healthcare provider draws a blood sample from a vein (usually in the arm).
- The sample is processed in the laboratory to measure AAT concentration using immunoturbidimetric or nephelometric methods.
- In suspected genetic deficiency, genotyping or phenotyping may be done to confirm SERPINA1 gene mutations.
Interpreting AAT Test Results
| Result Type | Possible Interpretation |
|---|---|
| Normal AAT | No deficiency or damage |
| Low AAT | Genetic AAT deficiency, liver disease, or protein loss |
| High AAT | Inflammation, infection, pregnancy, or cancer |
🔹 If AAT levels are low, genetic testing is recommended to confirm Alpha-1 Antitrypsin Deficiency.
Test Preparation
- No fasting required.
- Avoid getting the test during severe infection or inflammation, as AAT is an acute phase reactant and may appear falsely elevated.
- Inform your doctor if you have a family history of early emphysema or liver disease.
When to Consult a Doctor
Consult your doctor if you experience:
- Chronic cough, wheezing, or breathlessness
- Liver-related symptoms such as jaundice or abdominal swelling
- Unexplained fatigue or weakness
- Family history of lung or liver disease
- COPD symptoms at a young age or without smoking history
Your doctor may recommend an AAT Test if they suspect genetic deficiency or chronic lung/liver involvement.
Important Word Explanations
| Term | Simple Meaning |
|---|---|
| Alpha-1 Antitrypsin (AAT) | A protein that protects lung tissue from enzyme damage. |
| Neutrophil Elastase | An enzyme that helps fight infection but can damage lungs if unregulated. |
| AAT Deficiency | A genetic disorder causing low AAT levels. |
| COPD | Chronic Obstructive Pulmonary Disease – a lung condition that makes breathing difficult. |
| Serum | The liquid part of blood used for testing. |
| Acute Phase Reactant | A protein that increases during inflammation or infection. |
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