What this test measures
Alpha-1 antitrypsin (AAT) is a glycoprotein made by the liver that circulates in blood and travels to the lungs, where it neutralises neutrophil elastase — an enzyme that, if unchecked, breaks down lung tissue. The test quantifies AAT concentration in serum, reported in mg/dL.
AAT is also an acute-phase reactant, meaning it rises during inflammation, infection, pregnancy, and oestrogen use — so a "normal" or "high" value during acute illness does not rule out deficiency. Confirmatory testing for genetic deficiency uses phenotyping (PI typing) or genotyping for the common Z and S alleles.
Why it matters
AAT deficiency is one of the most common life-shortening genetic disorders in people of European descent but is much rarer in India — under-diagnosed rather than absent. It causes early-onset emphysema (typically panlobular, basal) in non-smokers in their 30s–50s, and liver disease in children and adults (cirrhosis, hepatocellular carcinoma). Testing is recommended in: every patient with COPD, any unexplained chronic liver disease in adults, neonatal jaundice that does not resolve, family history of AAT deficiency, and unexplained bronchiectasis.
A low AAT level (< 100 mg/dL or < 20 µmol/L) should always trigger genotyping. AAT is also used clinically as a non-specific inflammation marker — it rises 2–4 fold in acute inflammation alongside CRP and SAA.
How to prepare
No fasting needed. Avoid testing during an acute infection if the question is "deficiency" — inflammation falsely raises the level. Wait at least 2 weeks after recovery from any significant illness. Disclose pregnancy and any oestrogen-containing medications (combined oral contraceptive, hormone replacement) as these elevate AAT.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Alpha-1 Antitrypsin (mg/dL)[1][2][3] | 90 – 200 mg/dL (adults) | < 90 mg/dL: suggests AAT deficiency — refer for PI phenotyping or genotyping. < 50 mg/dL: severe deficiency (usually PiZZ homozygote); high risk of early emphysema and liver disease. | > 200 mg/dL: usually reflects acute-phase response — infection, inflammation, post-operative state, malignancy, pregnancy, or oestrogen use. Not clinically actionable on its own; assess CRP and clinical context. |
AAT levels and genotype correlation
| AAT (mg/dL) | Typical phenotype | Risk |
|---|---|---|
| 90 – 200 | PiMM (normal) | Baseline population risk |
| 60 – 100 | PiMZ / PiMS heterozygote | Mildly increased; smokers at higher risk |
| 40 – 60 | PiSZ | Moderate deficiency |
| < 50 | PiZZ (homozygote) | Severe deficiency; early emphysema and liver disease |
| > 200 | Acute-phase rise | Infection, inflammation, pregnancy, oestrogen |
Frequently asked questions
Who should be tested for AAT deficiency?
Anyone diagnosed with COPD or emphysema (especially under age 45 or in non-smokers), unexplained chronic liver disease, neonatal jaundice that persists, unexplained bronchiectasis, and first-degree relatives of a known AAT-deficient patient.
How is AAT deficiency inherited?
Autosomal codominant. Each parent contributes one of the SERPINA1 gene variants (M = normal, S = mild deficiency, Z = severe deficiency). PiZZ homozygotes have severe deficiency; PiMZ heterozygotes have mild deficiency and increased risk with smoking.
Why does smoking matter so much in AAT deficiency?
Cigarette smoke inactivates whatever AAT is present in the lungs and floods them with neutrophil elastase. A PiZZ smoker often develops disabling emphysema in their 30s; a PiZZ non-smoker may live decades longer with milder disease.
What is the treatment for AAT deficiency?
Stop smoking. Standard COPD treatment (inhalers, pulmonary rehab, vaccinations). In severe deficiency, weekly IV augmentation therapy with purified AAT is used in some countries — currently not widely available in India. Liver disease may need transplantation in severe cases.
Why might a normal AAT result still hide deficiency?
AAT rises during any inflammation. A PiMZ heterozygote with a chest infection may have a "normal" level — repeat testing after recovery, or proceed directly to genotyping if suspicion is high.
Is AAT deficiency common in India?
It is much rarer than in Europe but is under-diagnosed. Indian guidelines now recommend AAT testing in any COPD patient under 45, non-smoking COPD, unexplained adult cirrhosis, and family screening of confirmed cases.
Will my result tell me my genotype?
No — this test measures the protein level. If the level is low, a separate genotype or phenotype (PI typing) test confirms which variant you carry. This is critical for family counselling.
Related Immunology tests
Tests commonly ordered alongside ALPHA-1-ANTITRYPSIN (AAT), or that help interpret an unexpected result.
Sources & references
- NCBI StatPearls — Alpha 1 Antitrypsin Deficiency · accessed 2026-05-30T00:00:00.000Z
- NIH MedlinePlus — Alpha-1 Antitrypsin Test · accessed 2026-05-30T00:00:00.000Z
- Mayo Clinic Labs — Alpha-1 Antitrypsin · accessed 2026-05-30T00:00:00.000Z
- Alpha-1 Foundation — Testing and Diagnosis · accessed 2026-05-30T00:00:00.000Z
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