What are the initial laboratory tests for a patient suspected of having alpha 1 antitrypsin deficiency, particularly for an adult presenting with symptoms of Chronic Obstructive Pulmonary Disease (COPD) or liver disease?

Laboratory Testing for Alpha-1 Antitrypsin Deficiency

For adults with suspected alpha-1 antitrypsin (A1AT) deficiency presenting with COPD or liver disease, begin with serum A1AT level measurement, and if the level is <23 mmol/L (<1.2 g/L), proceed immediately to DNA sequencing of the SERPINA1 gene coding regions (exons 2-5). 1

Risk Stratification Determines Testing Pathway

The Canadian Thoracic Society 2025 guidelines provide a clear algorithmic approach based on clinical suspicion level 1:

High Clinical Suspicion (Simultaneous Testing)

Measure serum A1AT levels AND perform DNA sequencing of SERPINA1 gene simultaneously if the patient has ANY of these features 1:

• Early-onset COPD (age <40 years)
• COPD with minimal smoking history (<10 pack-years)
• Basal panlobular emphysema on imaging
• Family history of COPD or A1AT deficiency
• History of perinatal jaundice

Moderate Clinical Suspicion (Sequential Testing)

Start with serum A1AT level measurement, then proceed to DNA sequencing only if level is <23 mmol/L (<1.2 g/L) for patients with 1:

• COPD (without high-risk features)
• Unexplained bronchiectasis
• Adult-onset asthma with persistent airflow obstruction
• Liver cirrhosis
• Granulomatosis with polyangiitis (GPA) vasculitis or panniculitis

The Two Essential Tests

1. Serum A1AT Protein Level

• Collection method: Either serum or plasma is acceptable; most studies use serum (79.7%) 1
• Interpretation threshold: A level ≥23 mmol/L (≥1.2 g/L) rules out severe A1AT deficiency in moderate-risk patients 1
• Severe deficiency: <11 mmol/L (<0.57 g/L) 1
• Critical limitation: A1AT is an acute phase reactant that increases during inflammation, infection, or acute illness, making test-retest reproducibility weak 1

2. DNA Sequencing of SERPINA1 Gene

• Gold standard test: Sequence coding exons 2-5 of the SERPINA1 gene 1
• Superiority over traditional methods: Detects all >300 genetic variants in a single assay, including rare and dysfunctional variants (like Pi*F) that may show normal serum levels 1, 2
• Advantage over targeted genotyping: Traditional PCR-based genotyping only tests for PiS and PiZ alleles, missing other pathogenic variants 1
• Practical benefit: Genetic mutations are invariable, unlike fluctuating A1AT protein levels 1

Critical Testing Pitfalls to Avoid

Do not test during acute illness, recent surgery, or active inflammation - these conditions artificially elevate A1AT levels and can mask deficiency 2. The acute phase response can raise levels as high as 1.4 g/L even in deficient patients 1.

Do not rely solely on serum levels in high-risk patients - even with levels >23 mmol/L (>1.2 g/L), proceed to DNA sequencing if the patient has early-onset COPD, minimal smoking exposure, panlobular emphysema, or family history 1, 2.

Do not use liver biopsy for diagnosis - it is not recommended for diagnosing A1AT deficiency, though it may be used for staging liver disease severity in patients with clinically overt liver disease 2.

Family Screening Protocol

Test all first-degree relatives (parents, siblings, children) of confirmed A1AT-deficient patients with serum A1AT levels followed by genetic testing if indicated 2, 3. Siblings and offspring of a heterozygous individual have a 25% chance of being heterozygous themselves 3.

Practical Laboratory Considerations

• Single tube collection: It is possible to measure A1AT levels in plasma and sequence the gene from the buffy coat using one collection tube 1
• Unit reporting variability: Be aware that 12 different units of measurement are used across laboratories; 87.9% report in mass units (g/L or mg/dL) while 7.8% use molar units (mmol/L) 1
• Confirmatory testing: DNA sequencing provides definitive genotype classification (PiZZ, PiMZ, Pi*SZ, etc.) which is essential for accurate risk assessment and cannot be achieved by protein levels alone 1

When Genetic Testing Is Mandatory

Proceed directly to DNA sequencing regardless of serum level in these situations 1, 2:

• First-degree relatives of known A1AT-deficient patients (even if asymptomatic)
• Patients with intermediate A1AT deficits where overlapping levels across genotypes make differentiation impossible
• Any patient where precise genotype knowledge is needed for risk stratification and family counseling

Clinical Context for Testing

The irreversible nature of lung damage in A1AT deficiency makes early diagnosis critical 1. Delayed diagnosis (average 5.3 years after first symptoms) is associated with worse overall survival, transplant-free survival, reduced functional status, and diminished quality of life 1. Late diagnosis occurs at a mean FEV1 of 52% predicted, representing substantial irreversible damage 1.