What are the diagnostic steps and treatment options for alpha 1 antitrypsin deficiency?

Diagnosis of Alpha-1 Antitrypsin Deficiency

Who Should Be Tested

All patients with COPD, adult-onset asthma with persistent airflow obstruction (FEV1/FVC <0.7), and unexplained bronchiectasis should be tested for alpha-1 antitrypsin (A1AT) deficiency. 1 Additionally, testing is indicated for individuals with early-onset emphysema regardless of smoking history, liver disease of unknown cause, and family members of known A1AT-deficient patients. 2

Diagnostic Algorithm

The optimal diagnostic approach involves collecting two blood tubes simultaneously: a red-top tube for serum A1AT level measurement and a lavender-top tube for DNA analysis from the buffy coat. 1 This dual-tube approach allows for both quantitative and genetic confirmation in a single blood draw.

Step 1: Measure Serum A1AT Level

• Draw serum or plasma for A1AT quantification (these are considered equivalent). 1
• Critical caveat: Never test during acute illness, infection, or inflammatory states. 3 A1AT is an acute phase reactant and levels can rise to 1.4 g/L even in deficient patients during inflammation, creating false-negative results. 3
• If A1AT level is < 23 μmol/L (< 1.2 g/L), this indicates severe deficiency and warrants immediate genetic confirmation. 1, 2
• If A1AT level is ≥ 23 μmol/L (≥ 1.2 g/L) in moderate clinical suspicion cases, severe deficiency is ruled out. 2

Step 2: Genetic Confirmation

Phenotyping by isoelectric focusing (IEF) is the gold standard for diagnosis, but DNA sequencing of the SERPINA1 gene is increasingly preferred for definitive diagnosis. 1

• Phenotyping limitations: IEF can identify most common variants (PiZ, PiS) but may miss rare variants like M malton, M duarte, and null alleles. 1
• Genotyping advantages: DNA-based testing from genomic DNA extracted from circulating mononuclear blood cells provides definitive, invariable results. 1 Genetic mutations do not fluctuate like protein levels. 1
• For borderline or normal A1AT levels with high clinical suspicion, proceed directly to SERPINA1 DNA sequencing rather than repeat protein measurements. 1, 3

Key Diagnostic Pitfalls to Avoid

Do Not Rely on A1AT Level Alone

Serum A1AT protein level should never be used as the sole basis for establishing or excluding the diagnosis. 1 In heterozygotes (PiMZ), plasma levels are often normal, and even PiZZ patients can have transiently increased levels during systemic inflammation. 1

Recognize Rare Variants

• Some genetic variants produce normal circulating A1AT levels but the protein is nonfunctional (e.g., Pi*F variant). 1
• Rare M-like phenotypes (M malton, M duarte, S iiyama) may be undetectable by routine IEF and require DNA sequencing. 1
• Commercial test kits detecting only S and Z alleles will miss null alleles. 1

Timing of Testing Matters

Avoid testing during acute exacerbations, infections, or any inflammatory condition. 3 If initial testing occurs during acute illness and shows borderline results, do not simply repeat the A1AT level—proceed to genetic testing. 1, 3

Diagnostic Methods Comparison

Isoelectric Focusing (Phenotyping)

• Identifies AAT protein variants based on altered isoelectric point. 1
• Can be performed on serum, plasma, or dried blood spot samples. 1
• Dried blood spots are suitable for screening but require confirmation on serum/plasma. 1
• Limitation: Often fails with rare, unknown, or null alleles. 4

DNA Sequencing (Genotyping)

• Detects specific mutations in SERPINA1 gene. 1
• Results are reliable, definitive, and do not fluctuate. 1
• Used for prenatal diagnosis via chorionic villus sampling or amniocentesis. 1
• Limitation: Standard genotyping assays restricted to common variants; full gene sequencing needed for rare variants. 4

Special Populations

Liver Disease Diagnosis

For suspected A1AT deficiency-associated liver disease, phenotyping plus abdominal ultrasound establishes the diagnosis—liver biopsy is not necessary. 1 However, biopsy may be useful for staging severity or when multiple risk factors for liver disease coexist. 1

• PAS-diastase (PAS-D) positive inclusions >3 μm have 94% specificity for Pi*Z allele but only 47% sensitivity. 1
• Rule out other causes: viral hepatitis, hemochromatosis, Wilson's disease, alcoholic and autoimmune liver disease. 1

Prenatal and Neonatal Testing

• Prenatal diagnosis via amniocentesis or chorionic villus sampling uses DNA amplification techniques. 1
• Postnatal detection can utilize heel blood samples with DNA amplification. 1
• Risk of homozygous offspring is 25% when both parents are Pi*MZ carriers. 1

Nomenclature Considerations

The Canadian Thoracic Society recommends adopting HGVS (Human Genome Variation Society) nomenclature for genetic variants alongside traditional Pi typing during a transition period. 1 This improves accuracy in identifying rare variants and enables better registry data for research. 1