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

Diagnostic Criteria for Allergic Bronchopulmonary Aspergillosis (ABPA)

The 2024 revised ISHAM-ABPA working group consensus criteria require both 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

Patient Population and Clinical Context

Suspect ABPA in patients with:

• Predisposing conditions: asthma, cystic fibrosis, chronic obstructive lung disease, or bronchiectasis 1
• Compatible clinical presentations: expectoration of brown mucus plugs, poorly controlled asthma despite therapy, recurrent pulmonary infiltrates, fleeting opacities on imaging, finger-in-glove opacities, or lung collapse 1, 2

Essential Components (Both Required)

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

   • A positive type 1 skin test to Aspergillus is acceptable when IgE testing is unavailable 1, 2

2. Serum total IgE ≥500 IU·mL⁻¹ 1

   • Total IgE <500 IU·mL⁻¹ may be acceptable if all other criteria are fulfilled, particularly in patients with prior corticosteroid therapy, elderly patients, or those with constitutively low baseline IgE 1, 2

Other Components (Any Two Required)

1. Positive IgG against A. fumigatus 1

   • Use population-specific cut-offs: ≥27 mgA·L⁻¹ (India), ≥60 mgA·L⁻¹ (Japan), ≥40 mgA·L⁻¹ (UK) 1, 2
   • Use manufacturer recommendations when population-specific cut-offs unavailable 1
   • Can be detected using lateral flow assays or enzyme immunoassays 1

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

   • Historical values are acceptable 1, 2

3. Imaging findings consistent with ABPA 1

   • Thin-section chest CT showing: bronchiectasis (particularly central/proximal), mucus plugging, or high-attenuation mucus 1, 2
   • Fleeting opacities on chest radiograph consistent with ABPA 1

Pathognomonic Finding

High-attenuation mucus on chest CT is pathognomonic of ABPA and confirms the diagnosis even if all other criteria are not fulfilled. 1, 3, 2 This finding alone can establish the diagnosis regardless of other missing components.

Additional Supportive Features

• Elevated IgE against recombinant Aspergillus antigens (rAsp f1, f2, and f4) supports the diagnosis and can be used as another diagnostic component 1, 3
• Expectoration of mucus plugs, finger-in-glove opacities, fleeting opacities on chest radiograph, and lung collapse are important clinical considerations 1

Recommended Diagnostic Workup

Laboratory testing in suspected ABPA:

• Serum total IgE 2
• A. fumigatus-specific IgE 2
• A. fumigatus-specific IgG 2
• Peripheral blood eosinophil count 2

Imaging strategy:

• Thin-section chest CT is mandatory at baseline to identify and characterize bronchiectasis, mucus plugging, high-attenuation mucus, and other abnormalities 1, 2
• Chest radiograph can be used to assess treatment response 1, 2

Sputum culture is suggested during evaluation to identify species or guide therapy 1, 2

Bronchoscopy is not routinely recommended for diagnosing ABPA but may be necessary in specific situations such as uncertain diagnosis, suspected ABPM (allergic bronchopulmonary mycosis from non-Aspergillus fungi), unexplained hemoptysis, or suspicion of chronic infection 2

Critical Pitfalls to Avoid

• Do not use serum galactomannan for diagnosing ABPA 1
• Be aware that prior corticosteroid treatment can lower serum total IgE, potentially causing false-negative results if the 500 IU·mL⁻¹ threshold is rigidly applied 1
• Non-standardized assays for IgE and IgG against Aspergillus species carry high probability of misclassification 4
• Small amounts of "allergic" mucin in bronchial biopsies may contain degenerated eosinophils that resemble macrophages and can be overlooked 5
• Patients with ABPA may have atypical manifestations and not meet all standard diagnostic criteria, requiring high clinical suspicion 5, 6