What are the diagnostic criteria and treatment options for Allergic Bronchopulmonary Aspergillosis (ABPA)?

How to Diagnose ABPA

Diagnose ABPA using the 2024 revised ISHAM-ABPA working group criteria, which require a predisposing condition plus two essential components (A. fumigatus-specific IgE ≥0.35 kUA·L⁻¹ AND serum total IgE ≥500 IU·mL⁻¹) plus any two of three other components (positive A. fumigatus IgG, blood eosinophils ≥500 cells·μL⁻¹, or characteristic CT findings). 1

Clinical Context and Screening

Suspect ABPA in patients with:

• Predisposing conditions: asthma, cystic fibrosis, chronic obstructive lung disease, or bronchiectasis 1
• Characteristic clinical features: expectoration of brown mucus plugs, poorly controlled asthma despite therapy, recurrent pulmonary infiltrates, or fleeting opacities on imaging 1

Screen all asthmatic patients with Aspergillus sensitization by performing skin prick testing or measuring A. fumigatus-specific IgE, as approximately 20% of SPT-positive asthmatics will have ABPA 2. In cystic fibrosis patients, approximately 7% develop ABPA and warrant systematic screening 3.

Essential Diagnostic Components (Both Required)

1. A. fumigatus-specific IgE ≥0.35 kUA·L⁻¹

• This is mandatory for diagnosis 1
• If unavailable, a positive type 1 skin test to Aspergillus is acceptable 1

2. Serum total IgE ≥500 IU·mL⁻¹

• This threshold has 71.8% level of consensus 1
• Important caveat: Total IgE <500 IU·mL⁻¹ may be acceptable if all other criteria are fulfilled, particularly in patients with prior corticosteroid therapy which can suppress IgE levels 1, 4

Additional Components (Any Two Required)

1. Positive IgG against A. fumigatus

• Use population-specific cut-offs when available (≥27 mgA·L⁻¹ for India, ≥60 mgA·L⁻¹ for Japan, ≥40 mgA·L⁻¹ for UK) 1
• When population data unavailable, use manufacturer-recommended cut-offs 1
• Can be detected using lateral flow assays or enzyme immunoassays 1

2. Blood eosinophil count ≥500 cells·μL⁻¹

• Historical values are acceptable (patient doesn't need to be eosinophilic at time of diagnosis) 1
• This criterion has 73.0% level of consensus 1

3. Characteristic imaging findings

• Thin-section chest CT (strongly recommended at baseline with 92.3% consensus) showing: 1
  • Central bronchiectasis (bilateral, virtually pathognomonic) 2
  • Mucus plugging
  • High-attenuation mucus (pathognomonic - confirms ABPA even if other criteria not fulfilled) 1
• Chest radiograph showing fleeting opacities or finger-in-glove opacities 1

Recommended Laboratory Workup

In asthmatic patients with Aspergillus sensitization, perform: 1

• Serum total IgE (89.7% consensus)
• A. fumigatus-specific IgG (82.1% consensus)
• Peripheral blood eosinophil count (87.2% consensus)

Tests NOT Recommended

• Serum galactomannan - do not use for diagnosing ABPA (92.3% consensus against) 1

Imaging Strategy

Initial Diagnosis

• Thin-section chest CT is mandatory at baseline to identify and characterize bronchiectasis, mucus plugging, high-attenuation mucus, and other abnormalities 1
• In children, carefully consider radiation dosage 3

Follow-up

• Use chest radiograph (not CT) to assess treatment response (62.3% consensus) 1

Role of Bronchoscopy and Sputum Culture

Bronchoscopy

Not routinely recommended for diagnosing ABPA (86.1% consensus) 1. However, perform bronchoscopy in these specific situations: 1

• Uncertain diagnosis
• Suspected ABPM where sputum cultures are uninformative or cannot be obtained
• Unexplained hemoptysis
• Suspicion of chronic infection (tuberculosis or non-tuberculous mycobacteria) before initiating systemic glucocorticoids

Therapeutic bronchoscopy may be required for mucus plug removal in respiratory failure or recalcitrant mucus plugs despite systemic therapy 1

Sputum Culture

• Suggested during ABPA evaluation to help identify species or guide therapy (61.5% consensus) 1
• Recommended during evaluation of ABPM (100% consensus) 1

Common Pitfalls to Avoid

1. Missing atypical presentations: Patients may not meet all traditional criteria, especially if previously treated with corticosteroids which can suppress IgE levels and alter radiographic findings 4, 5

2. Overlooking "allergic" mucin on bronchial biopsy: In small biopsy fragments, mucin may be present in small amounts with degenerated eosinophils resembling macrophages 5

3. Failing to screen high-risk populations: All asthmatics with Aspergillus sensitization and all cystic fibrosis patients warrant systematic evaluation 3, 2

4. Ignoring high-attenuation mucus: This finding is pathognomonic and confirms ABPA diagnosis even when other criteria are incomplete 1

5. Ordering unnecessary tests: Avoid serum galactomannan and routine bronchoscopy, which add cost without diagnostic benefit 1

Additional Supportive Findings

While not required for diagnosis, these findings support ABPA: 1

• Elevated IgE against recombinant Aspergillus antigens (rAsp f1, f2, and f4)
• Finger-in-glove opacities on chest radiograph
• Lung collapse
• Band shadows or "ring sign" or parallel "tram lines" on imaging 3