What are the diagnostic criteria for Bronchopulmonary Aspergillosis (BPA)?

Diagnostic Criteria for Bronchopulmonary Aspergillosis (BPA)

According to the 2024 revised International Society for Human and Animal Mycology (ISHAM) consensus guidelines, the diagnosis of Bronchopulmonary Aspergillosis requires specific predisposing conditions or compatible clinical presentation, two essential components, and at least two additional components from a defined list. 1

Predisposing Conditions

• Asthma
• Cystic fibrosis
• Chronic obstructive lung disease
• Bronchiectasis
• OR a compatible clinico-radiological presentation (expectoration of mucus plugs, fleeting opacities on chest imaging, finger-in-glove opacities, lung collapse)

Essential Components (both required)

• A. fumigatus-specific IgE ≥0.35 kUA·L⁻¹
• Serum total IgE ≥500 IU·mL⁻¹

Other Components (at least two required)

• Positive IgG against A. fumigatus
• Blood eosinophil count ≥500 cells·μL⁻¹ (could be historical)
• Thin-section chest CT consistent with ABPA (bronchiectasis, mucus plugging and high-attenuation mucus) or fleeting opacities on chest radiograph

Important Considerations

• High-attenuation mucus on CT is pathognomonic and confirms ABPA diagnosis even if other criteria are not fulfilled
• A positive type 1 skin test is acceptable when Aspergillus-IgE testing is unavailable
• Serum total IgE <500 IU·mL⁻¹ may be acceptable if all other criteria are fulfilled
• Low serum total IgE can occur with prior glucocorticoid treatment, in elderly patients, or in those with constitutively low IgE
• Elevated IgE against recombinant Aspergillus antigens (rAsp f1, f2, and f4) supports the diagnosis

Diagnostic Algorithm

1. Start with A. fumigatus-specific IgE testing
2. If ≥0.35 kUA·L⁻¹, measure serum total IgE
3. If total IgE ≥500 IU·mL⁻¹, proceed with additional testing:
   • A. fumigatus-specific IgG
   • Peripheral blood eosinophil count
   • Chest CT
   • Lung function tests

Radiological Classification of ABPA

The 2024 ISHAM guidelines classify ABPA into five radiological categories 1:

1. ABPA-S (Serological): ABPA with no bronchiectasis
2. ABPA-B: ABPA with bronchiectasis
3. ABPA-MP: ABPA with mucus plugging but without high-attenuation mucus
4. ABPA-HAM: ABPA with high-attenuation mucus
5. ABPA-CPF: ABPA with chronic pleuropulmonary fibrosis (two or more of: pulmonary fibrosis, fibro-cavitary lesions, fungal ball, pleural thickening)

Allergic Bronchopulmonary Mycosis (ABPM)

For non-Aspergillus fungal causes, similar criteria apply with key differences:

• A. fumigatus-specific IgE should be <0.35 kUA·L⁻¹
• Elevated fungus-specific IgE for the causative organism
• Two sputum cultures or one bronchoalveolar lavage fluid culture growing the causative fungus
• Absence of elevated IgE against rAsp f1, f2, and f4 excludes ABPA and supports ABPM

Common Pitfalls in Diagnosis

• Failure to consider ABPA in patients without asthma or cystic fibrosis
• Overlooking ABPA in patients with normal total IgE due to prior steroid treatment
• Missing the diagnosis in elderly patients who may have lower IgE levels
• Not recognizing high-attenuation mucus as pathognomonic for ABPA
• Confusing ABPA-CPF with chronic pulmonary aspergillosis, which requires exclusion

The British Thoracic Society guidelines (2019) also emphasize that ABPA should be investigated in all newly presenting patients with bronchiectasis 1, noting that ABPA is a common cause of bronchiectasis in the UK (1-11% of cases).

Early diagnosis and treatment are critical to prevent recurrent exacerbations and long-term complications, particularly bronchiectasis progression, which significantly impacts morbidity and mortality 2.