Diagnosis of Allergic Bronchopulmonary Aspergillosis (ABPA)
The diagnosis of ABPA requires asthma or cystic fibrosis as the underlying condition, plus blood eosinophil count ≥500 cells/μL, serum total IgE ≥500 IU/mL, elevated Aspergillus fumigatus-specific IgG or positive lateral flow assay, and characteristic findings on thin-section chest CT. 1
Essential Diagnostic Criteria
The 2024 ISHAM-ABPA working group guidelines provide the most current diagnostic framework 1:
Core Requirements (All Must Be Present):
- Underlying condition: Asthma or cystic fibrosis
- Blood eosinophil count: ≥500 cells/μL
- Serum total IgE: ≥500 IU/mL
- Aspergillus-specific serology: Elevated A. fumigatus-IgG or positive lateral flow assay
- Imaging: Thin-section chest CT showing characteristic features
Alternative Diagnostic Pathway:
If the above criteria are not fully met, diagnosis can be established with two of the following 1:
- Blood eosinophil count ≥500 cells/μL
- Fungus-specific IgG elevation
- Fleeting chest radiographic opacities
- Abnormal chest CT findings
Clinical Classification Based on Imaging
The diagnosis should specify the subtype based on CT findings 1:
- ABPA-S (serological): No bronchiectasis, no mucus plugs
- ABPA-B: Bronchiectasis present
- ABPA-MP: Mucus plugging present
- ABPA-HAM: High-attenuation mucus visible
- ABPA-CPF: Chronic pleuropulmonary fibrosis
Key Imaging Features
Central bronchiectasis (inner two-thirds of chest) is pathognomonic 2. Additional CT findings include:
- Transient pulmonary infiltrates (upper lobe predominance)
- Mucoid impaction creating "glove-finger" or band shadows
- "Ring sign" or "tram lines" representing inflamed bronchi 3
- Tree-in-bud pattern may occasionally be present 1
Critical Diagnostic Pitfalls
Do Not Confuse With:
Severe asthma with fungal sensitization: Patients may have elevated total IgE and Aspergillus sensitization but don't meet full ABPA criteria 1
Aspergillus bronchitis: At least two positive respiratory samples with Aspergillus, may have elevated IgG and bronchiectasis, but lacks other ABPA criteria 1
Chronic pulmonary aspergillosis (CPA): Distinguished by cavitary disease, fungus balls, and typically occurs in non-asthmatics with structural lung disease. May have elevated Aspergillus-IgE but lacks the eosinophilia and asthma background 4
Primary ciliary dyskinesia: Presents with bronchiectasis and recurrent infections but has situs inversus in 55% of cases, very low nasal nitric oxide, and abnormal ciliary ultrastructure 2
Important Caveats:
ABPM (Allergic Bronchopulmonary Mycosis): When fungi other than Aspergillus cause the syndrome, the absence of elevated IgE against rAsp f1, f2, and f4 strongly supports ABPM over ABPA 1
Coexisting conditions: ABPA patients may have additional causes of bronchiectasis (immunodeficiencies, ciliary disorders, mycobacterial infection), requiring workup including complete blood count, sweat chloride test, immunoglobulin levels, and mycobacterial cultures 1
Caution in non-asthmatics: A. fumigatus-specific IgE and IgG can be elevated in COPD, pulmonary tuberculosis, and bronchiectasis without ABPA 1
Laboratory Confirmation
Respiratory cultures showing Aspergillus support but do not confirm the diagnosis alone 4. Multiple samples increase yield 4. PCR is more sensitive than culture and strong signals indicate high fungal load 4.
Serology standardization: Use validated assays for Aspergillus-specific IgE and IgG; non-standardized assays may misclassify ABPA as ABPM 1.