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

ABPA Diagnostic Criteria

The 2024 revised ISHAM-ABPA working group consensus criteria require two essential components (A. fumigatus-specific IgE ≥0.35 kUA·L⁻¹ AND serum total IgE ≥500 IU·mL⁻¹) plus any two additional components from a defined list, in patients with predisposing conditions or compatible clinical presentation. 1, 2

Patient Population to Screen

Suspect ABPA in patients with: 1

• Predisposing conditions: Asthma, cystic fibrosis, COPD, or bronchiectasis
• Compatible clinical presentation: Expectoration of mucus plugs, fleeting opacities on imaging, finger-in-glove opacities, or lung collapse

Essential Components (BOTH Required)

1. A. fumigatus-specific IgE ≥0.35 kUA·L⁻¹ 1, 2

   • If unavailable, a positive type 1 skin test to Aspergillus is acceptable 1

2. Serum total IgE ≥500 IU·mL⁻¹ 1, 2

   • May accept <500 IU·mL⁻¹ if all other criteria are fulfilled (seen with prior glucocorticoid treatment, elderly patients, or constitutively low baseline IgE) 1

Additional Components (ANY TWO Required)

1. Positive IgG against A. fumigatus 1, 3

   • Use population-specific cut-offs: ≥27 mgA·L⁻¹ (India), ≥60 mgA·L⁻¹ (Japan), ≥40 mgA·L⁻¹ (UK) 1
   • If population-specific data unavailable, use manufacturer recommendations 1
   • Detected via lateral flow assays or enzyme immunoassays 1, 3

2. Blood eosinophil count ≥500 cells·μL⁻¹ (can be historical) 1, 2

3. Thin-section chest CT findings consistent with ABPA: 1, 2

   • Bronchiectasis (typically central)
   • Mucus plugging
   • High-attenuation mucus (HAM)
   • OR fleeting opacities on chest radiograph 1

Pathognomonic Finding

High-attenuation mucus on CT is pathognomonic and confirms ABPA diagnosis even if other criteria are not completely fulfilled. 1, 2 This finding alone can establish the diagnosis when clinical suspicion is high.

Advanced Diagnostic Markers

Elevated IgE against recombinant A. fumigatus antigens (rAsp f1, f2, and f4) supports the diagnosis and can be used as another diagnostic component. 1, 2

Recommended Diagnostic Workup

• Thin-section chest CT at baseline to identify bronchiectasis, mucus plugging, HAM, and other abnormalities (strongly recommended) 1
• Sputum fungal culture suggested to identify species and guide therapy 1
• Do NOT use serum galactomannan for diagnosis 1
• Bronchoscopy NOT routinely recommended 1

Critical Pitfalls to Avoid

• Prior corticosteroid therapy can lower serum total IgE below 500 IU·mL⁻¹, potentially causing missed diagnosis 1, 4
• Non-standardized assays for Aspergillus IgE and IgG have high probability of misclassification 3
• Small amounts of allergic mucin in bronchial biopsies may contain degenerated eosinophils resembling macrophages, easily overlooked 5
• Patients may present with atypical manifestations not meeting all traditional criteria, requiring high clinical suspicion 5, 4

Distinguishing ABPA from ABPM

For allergic bronchopulmonary mycosis (ABPM) caused by fungi other than A. fumigatus, the criteria differ slightly: 1, 2

• A. fumigatus-IgE should be <0.35 kUA·L⁻¹ 1
• Requires elevated fungus-specific IgE to the causative organism
• Two sputum cultures (or one BAL) growing the causative fungus becomes an additional component option 1, 2
• Absence of elevated IgE against rAsp f1, f2, and f4 strongly supports ABPM over ABPA 1