Diagnostic Criteria for Allergic Bronchopulmonary Aspergillosis (ABPA)
The diagnosis of ABPA requires predisposing conditions or compatible clinical presentation, plus two essential components (A. fumigatus-specific IgE ≥0.35 kUA·L−1 and serum total IgE ≥500 IU·mL−1), along with any two additional components from the established criteria. 1
Predisposing Conditions and Clinical Presentation
- ABPA should be suspected in patients with predisposing conditions (asthma, cystic fibrosis, COPD, bronchiectasis) or compatible clinico-radiological presentation 1
- Compatible clinical presentations include expectoration of mucus plugs, fleeting opacities on chest imaging, finger-in-glove opacities, and lung collapse 1
Essential Diagnostic Components
Other Components (any two required)
- Positive IgG against A. fumigatus 1
- Blood eosinophil count ≥500 cells·μL−1 (could be historical) 1
- Thin-section chest CT consistent with ABPA (bronchiectasis, mucus plugging, and high-attenuation mucus) or fleeting opacities on chest radiograph consistent with ABPA 1
Important Diagnostic Considerations
- High-attenuation mucus on CT is pathognomonic of ABPA and confirms diagnosis even if all other criteria are not fulfilled 1, 2
- A positive type 1 skin test is acceptable when Aspergillus-IgE testing is unavailable 1, 2
- Serum total IgE <500 IU·mL−1 may be acceptable if all other criteria are fulfilled 1, 2
- A. fumigatus-specific IgG can be detected using lateral flow assays or enzyme immunoassays with population-specific cut-offs (e.g., ≥27 mgA·L−1 for India, ≥60 mgA·L−1 for Japan, and ≥40 mgA·L−1 for the UK) 1
- Elevated IgE against recombinant A. fumigatus allergens (rAsp f1, f2, and f4) supports the diagnosis of ABPA and can be used as another diagnostic component 1, 2, 3
Radiological Features
- Chest CT findings include bronchiectasis, mucus plugging, high-attenuation mucus, and fleeting opacities 1, 4
- Radiological classification of ABPA includes five categories 2:
- ABPA-S: Serological ABPA without bronchiectasis
- ABPA-B: ABPA with bronchiectasis
- ABPA-MP: ABPA with mucus plugging
- ABPA-HAM: ABPA with high-attenuation mucus
- ABPA-CPF: ABPA with chronic pleuropulmonary fibrosis
Diagnostic Algorithm
- Suspect ABPA in patients with predisposing conditions or compatible clinical presentation 1
- Perform A. fumigatus-specific IgE testing 1
- If A. fumigatus-specific IgE ≥0.35 kUA·L−1, measure serum total IgE 1
- If serum total IgE ≥500 IU·mL−1, proceed with additional testing for A. fumigatus-specific IgG, peripheral blood eosinophil count, and chest CT 1
- Diagnose ABPA if both essential components and at least two other components are present 1
Distinguishing ABPA from ABPM
- ABPM (Allergic Bronchopulmonary Mycosis) should be considered when A. fumigatus-specific IgE is <0.35 kUA·L−1 but other fungi are implicated 1
- ABPM diagnosis requires elevated fungus-specific IgE, serum total IgE ≥500 IU·mL−1, plus two of the following: positive fungus-specific IgG, blood eosinophil count ≥500 cells·μL−1, two sputum or one BAL fluid culture growing the causative fungus, or compatible radiological findings 1
- The absence of elevated IgE against rAsp f1, f2, and f4 excludes ABPA and strongly supports the diagnosis of ABPM 1, 3
Diagnostic Pitfalls and Caveats
- Low serum total IgE (<500 IU·mL−1) can occur in patients with prior glucocorticoid treatment, the elderly, or those with constitutively low IgE before developing ABPA 1
- Commercial assays for detecting IgE and IgG against fungi other than Aspergillus species are limited, making ABPM diagnosis challenging 1
- Bronchoscopy with biopsy is not routinely recommended for diagnosing ABPA but may be helpful in atypical presentations 1, 5
- Different diagnostic algorithms may yield different prevalence rates of ABPA, with varying sensitivity and specificity 6
- ABPA can occur in patients with a history of pulmonary tuberculosis, potentially with more severe immunologic parameters 7