Definition

Alpha-1 antitrypsin (AAT) is a lab test to measure the amount of AAT in your blood. The test is also done to check for abnormal forms of AAT.

Alternative Names

A1AT test

How the Test is Performed

A blood sample is needed.

How to Prepare for the Test

There is no special preparation.

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.

Why the Test is Performed

This test is helpful in identifying a rare form of emphysema in adults and a rare form of liver disease (cirrhosis) in children and adults caused by an AAT deficiency. AAT deficiency is passed down through families. The condition causes the liver to make too little of AAT, a protein that protects the lungs and liver from damage.

Everyone has two copies of the gene that makes AAT. People with two variant copies of the gene have lower blood levels and are at risk for more severe disease. Different gene variants may cause differing severity of illness.

Normal Results

Normal value ranges may vary slightly among different laboratories. Talk to your health care provider about the meaning of your specific test results.

What Abnormal Results Mean

A lower-than-normal level of AAT may be associated with:

• Damage of the large airways in the lungs (bronchiectasis)
• Scarring of the liver (cirrhosis)
• Chronic obstructive pulmonary disease (COPD)
• Liver tumors
• Yellowing of the skin and eyes due to blocked bile flow (obstructive jaundice)
• High blood pressure in the large vein that leads to the liver (portal hypertension)

Risks

There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another, and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight, but may include:

• Fainting or feeling lightheaded
• Multiple punctures to locate veins
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk anytime the skin is broken)

References

Dietzen DJ, Willrich MAV. Amino acids, peptides, and proteins. In: Rifai N, Chiu RWK, Young I, Burnham C-AD, Wittwer CT, eds. Tietz Textbook of Laboratory Medicine. 7th ed. St Louis, MO: Elsevier; 2023:chap 31.

Han MK, Lazarus SC. COPD: diagnosis and management. In: Broaddus VC, Ernst JD, King TE, et al, eds. Murray and Nadel's Textbook of Respiratory Medicine. 7th ed. Philadelphia, PA: Elsevier; 2022:chap 64.

Masson VK, Boas SR. a1 - Antitrypsin deficiency and emphysema. In: Kliegman RM, St. Geme JW, Blum NJ, et al, eds. Nelson Textbook of Pediatrics. 22nd ed. Philadelphia, PA: Elsevier; 2025:chap 442.