Alpha-1-Antitrypsin Deficiency

Alpha-1-antitrypsin deficiency (AATD) is an inherited, substantially underdiagnosed disorder of the SERPINA1 gene on chromosome 14, which encodes alpha-1 antitrypsin (AAT) — a serine protease inhibitor made mainly in the liver and released into the circulation, where its principal job is protecting the delicate elastin architecture of the alveoli from neutrophil elastase.^[1]

AATD produces two clinically opposite disease mechanisms in two different organs, and understanding that difference is the single most important concept in this chapter:

• Lung disease is a loss-of-function problem. Too little functional AAT reaches the alveoli, leaving neutrophil elastase unopposed to progressively destroy alveolar walls — producing early-onset, basal-predominant panacinar emphysema, often decades before the age typically associated with smoking-related COPD.
• Liver disease is a toxic gain-of-function problem. The abnormal Z-variant AAT protein misfolds and polymerizes inside hepatocytes instead of being secreted normally, and it is this intracellular accumulation — not a lack of circulating AAT — that injures the liver, driving neonatal cholestasis, chronic hepatitis, cirrhosis, and hepatocellular carcinoma risk.

Because these are two different mechanisms, intravenous augmentation therapy — which simply raises circulating AAT — treats the lung disease and does nothing for the liver disease. This distinction, and the equally important question of who should be tested in the first place, run through the entire chapter.^[2]

The clinically significant severe-deficiency genotype is homozygosity for the Z allele (PiZZ). AATD is estimated to affect roughly 1 in 2,000-5,000 people of European ancestry, yet diagnosis is typically delayed for years after the first symptoms, because both the lung and liver presentations are easily mistaken for far more common diagnoses — usual COPD, asthma, or cryptogenic liver disease — unless a clinician specifically thinks to test for it.^[3]

• Homozygosity for the Z allele (PiZZ) — the clinically significant severe-deficiency genotype and the greatest risk factor for both lung and liver disease.
• Compound heterozygous genotypes such as PiSZ — intermediate risk, clinically meaningful especially with smoking or alcohol exposure, but lower absolute risk than PiZZ.
• PiMZ heterozygosity ("carrier" status) — not generally associated with a significantly increased risk of clinical emphysema in a nonsmoker, but risk rises meaningfully with smoking.
• A first-degree relative with confirmed AATD, or with early-onset emphysema or unexplained liver disease that was never formally worked up.
• Cigarette smoking — by far the single largest modifiable risk factor for lung disease in a person with a deficiency genotype (see Non-Pharmacologic Treatment).
• Occupational dust, fume, or biomass-fuel exposure — the same lung-disease risk factors that apply in ordinary COPD compound the risk in AATD.
• Alcohol use, and other coexisting liver insults such as viral hepatitis or metabolic dysfunction-associated steatotic liver disease — these compound, rather than cause, AATD-related liver injury.

Step 1 — serum AAT level

Serum AAT level (usually measured by nephelometry) is the standard first test for a patient with moderate clinical suspicion. Because AAT is an acute-phase reactant, a level drawn during active infection or inflammation can be falsely normal or elevated in a genuinely deficient patient — check a concurrent CRP, and repeat testing once any acute illness has resolved if the result is inconsistent with the clinical picture.^[2]

Step 2 — genotype/phenotype confirmation

A low or borderline serum level should be confirmed with Pi genotyping or phenotyping (isoelectric focusing, sometimes called Pi typing) and/or SERPINA1 gene sequencing, which also detects rare null and deficient variants that isoelectric focusing alone can miss. For a patient with high pre-test clinical suspicion — for example, a sibling of a confirmed PiZZ patient, or classic early-onset basal emphysema — current Canadian guidance supports going directly to genetic testing rather than starting with a serum level.^[2]

Confirming and staging lung disease

Once a severe-deficiency genotype is confirmed, obtain spirometry and assess for emphysema exactly as in ordinary COPD — see the COPD chapter's Assessment & Diagnosis for the full post-bronchodilator spirometry criteria and GOLD grading, which apply unchanged here. Chest CT in AATD-related emphysema characteristically shows a basal-predominant panacinar pattern, a genuinely useful distinguishing feature from the apical-predominant centrilobular emphysema typical of ordinary smoking-related COPD, though it is a supportive finding rather than a diagnostic requirement.

Confirming and staging liver disease

Obtain baseline and periodic liver enzymes, and refer to hepatology for any abnormality. Once cirrhosis is identified, stage and manage it exactly as in the Cirrhosis chapter — Child-Pugh and MELD scoring, hepatocellular carcinoma surveillance, and the same transplant-referral triggers (a first decompensation event, or MELD ≥15) apply without modification for an AATD-related cause.

• Achieve smoking cessation — the single highest-impact intervention available, and dramatically more important in AATD than in ordinary COPD (see Non-Pharmacologic Treatment).
• Control lung symptoms and slow the rate of lung function decline using standard COPD pharmacotherapy (see the COPD chapter), layered with augmentation therapy in eligible patients.
• Correctly determine augmentation-therapy eligibility and, where eligible, arrange access without unnecessary delay.
• Detect and manage AATD-related liver disease early, understanding that augmentation therapy plays no role in that management (see the Cirrhosis chapter for the actual liver-directed treatment ladder).
• Recognize and treat AATD-associated panniculitis.
• Complete genetic counseling and offer cascade testing to first-degree relatives.
• Keep vaccination status current (see the COPD and Cirrhosis chapters).

Smoking cessation — even more important than in ordinary COPD

Smoking cessation is the single most important intervention for anyone with a severe-deficiency genotype, and its impact is dramatically larger in AATD than in the general COPD population: a person with a severe-deficiency genotype who continues smoking loses lung function far faster than one who has never smoked or who quits early, often developing symptomatic emphysema decades earlier than they otherwise would.^[3] Use the same behavioural-counselling-plus-pharmacotherapy approach described in the COPD chapter (varenicline, nicotine replacement therapy, bupropion) — there is nothing AATD-specific about the cessation regimen itself, only about how much is at stake in using it.

Avoid occupational and environmental lung insults

Minimize occupational dust/fume exposure and indoor/outdoor air pollution — the same general measures as in ordinary COPD, again disproportionately consequential given the underlying deficiency.

Protect the liver

Avoid or strictly limit alcohol, and manage coexisting metabolic risk factors (obesity, diabetes) that independently worsen liver outcomes — see the Cirrhosis chapter's Non-Pharmacologic Treatment for the full nutrition, alcohol, and surveillance guidance, which applies unchanged once AATD-related liver disease is present.

Vaccination and pulmonary rehabilitation

Follow the COPD chapter's vaccination schedule and pulmonary rehabilitation referral guidance in full; also ensure hepatitis A and hepatitis B vaccination, if non-immune, once liver disease is present, per the Cirrhosis chapter.

Genetic counseling and cascade family testing

AATD is inherited in an autosomal codominant pattern — both SERPINA1 alleles contribute to the phenotype, so parents, siblings, and children of a confirmed patient are each at meaningful risk and should be offered testing, regardless of whether they currently have symptoms. Counsel that an asymptomatic relative who tests positive still benefits from early identification — earlier smoking-avoidance counselling, earlier recognition of respiratory or liver symptoms, and earlier access to augmentation therapy if lung disease eventually develops.^[1]

Pregnancy

Augmentation therapy has not been studied in pregnancy — no controlled reproduction studies exist for the currently available product, and it should be continued or started in pregnancy only if the treating specialist judges the benefit clearly outweighs the unknown risk. Standard inhaled bronchodilator therapy is generally continued through pregnancy as described in the COPD chapter, since undertreated maternal hypoxemia poses a greater fetal risk than these agents. Smoking cessation is, if anything, even more urgent in a pregnant patient with a severe-deficiency genotype.

Breastfeeding

No data exist on whether augmentation-therapy A1-PI passes into breast milk; weigh the infant's breastfeeding benefit against the mother's clinical need for the infusion on a case-by-case, specialist-directed basis.

Pediatrics

Augmentation therapy is not authorized for use under age 18 — no pediatric studies have been performed, and the approved indication is adult emphysema only. A child with AATD-related liver disease (classically neonatal cholestatic jaundice) is managed by pediatric hepatology using standard pediatric liver-disease supportive care; augmentation therapy has no role here regardless of age, for the same liver-mechanism reason it has no role in adult AATD-related liver disease.

PiSZ and other intermediate genotypes

Augmentation-therapy candidacy in a PiSZ (or other non-PiZZ severe-deficiency) genotype is individualized with specialist input rather than applied automatically — the eligibility criteria in Choose Initial Treatment were established primarily in PiZZ populations.

Post-lung-transplant

Augmentation therapy is not indicated after lung transplantation, since the transplanted lung does not carry the recipient's genetic deficiency.

Hepatic and renal impairment

Dose adjustment of augmentation therapy for hepatic or renal impairment has not been studied — the product monograph gives no adjustment guidance, and dosing is unchanged regardless of liver status, since the drug is given intravenously rather than hepatically processed the way an oral drug would be. This does not mean augmentation therapy is expected to help the liver disease — see Choose Initial Treatment.

Older adults

Only a small number of patients aged 65 and older were included in the pivotal trials — not enough to determine whether older adults respond differently. Individualize based on overall clinical status; no specific dose adjustment is recommended for age alone.

• Spirometry approximately annually, or per the interval the treating respirology team specifies — see the COPD chapter for the full monitoring approach, which applies unchanged.
• Liver enzymes periodically, and, once cirrhosis is present, the full Cirrhosis-chapter monitoring schedule (electrolytes during diuretic titration, INR/albumin/bilirubin for Child-Pugh/MELD, hepatocellular carcinoma surveillance every 6 months indefinitely).
• Confirm ongoing smoking abstinence at every visit — relapse is itself grounds to pause augmentation-therapy eligibility.
• Track augmentation-therapy infusion adherence, and confirm the patient (or a trained caregiver) is administering it correctly if self-infusing at home.
• Reassess for new or recurrent panniculitis lesions.
• Confirm cascade family testing has actually been completed, not just discussed — this is easy to raise once and never follow up on.
• Keep vaccination status current per the COPD and Cirrhosis chapters.

1. Continued rapid lung function decline despite augmentation therapy and optimized COPD pharmacotherapy — first confirm infusion adherence and confirm smoking cessation has actually been sustained (not just reported), since both are common, correctable causes of apparent treatment failure before assuming the therapy itself has failed.
2. If adherence and cessation are both confirmed and decline continues, refer to a specialist AATD/respirology program for reassessment, including consideration of lung transplant referral using the same general triggers as in the COPD chapter's escalation pathway.
3. Progressive liver disease — there is no separate AATD-specific liver escalation pathway; follow the Cirrhosis chapter's Treatment Failure / Next Step ladder exactly (refractory ascites, recurrent hepatic encephalopathy, and the MELD ≥15/first-decompensation transplant-referral trigger all apply unmodified).
4. Panniculitis not responding to dapsone — reassess the diagnosis (confirm biopsy findings and AATD status), then add or switch to augmentation therapy; refer dermatology if lesions remain refractory.
5. A patient who appears to meet augmentation-therapy criteria but has been denied or delayed access — confirm the request was submitted correctly through the Canadian Blood Services Plasma Protein and Related Products Formulary pathway (or the Quebec-specific Prolastin-C pathway for Quebec residents) rather than assuming ineligibility; access-process errors are a real, correctable cause of a patient not receiving therapy they qualify for.

• Assuming augmentation therapy treats or slows AATD-related liver disease — it does not, and prescribing it for that reason is a genuine, avoidable error.
• Not testing a patient with COPD diagnosed young, or with a minimal smoking history, simply because they already carry a COPD diagnosis.
• Offering augmentation-therapy referral to a patient who is still smoking, rather than securing cessation first.
• Treating a PiMZ heterozygote as an augmentation-therapy candidate.
• Diagnosing panniculitis as cellulitis and giving a course of antibiotics instead of recognizing the pattern and biopsying.
• Interpreting a normal or borderline serum AAT level drawn during an acute illness as excluding AATD, without accounting for its behaviour as an acute-phase reactant.
• Re-deriving a separate bronchodilator regimen for AATD-related COPD instead of using the COPD chapter's GOLD ABE algorithm directly.
• Discussing family cascade testing once and never confirming it was actually completed.
• Missing hepatocellular carcinoma surveillance once AATD-related cirrhosis is identified — the same error flagged in the Cirrhosis chapter.

How to use this table: Doses are adult doses and require patient-specific confirmation. This table covers only the therapy genuinely specific to AATD — augmentation therapy and panniculitis treatment. For standard COPD bronchodilator/inhaled-corticosteroid/biologic dosing and the acute-exacerbation antibiotic ladder, see the COPD chapter's Drug Tables. For diuretics, nonselective beta-blockers, lactulose/rifaximin, and spontaneous bacterial peritonitis prophylaxis once cirrhosis is confirmed, see the Cirrhosis chapter's Drug Tables. Select any drug name to open its complete Pharmasist Drug Database page.

Augmentation therapy

The only agents that raise circulating alpha-1 proteinase inhibitor (A1-PI) levels; indicated only for the specific adult emphysema criteria in Choose Initial Treatment.

Panniculitis therapy