From the Guidelines
For suspected Allergic Bronchopulmonary Aspergillosis (ABPA), the key blood tests to order include total serum IgE, Aspergillus-specific IgE, Aspergillus-specific IgG, and peripheral blood eosinophil count, as recommended by the revised ISHAM-ABPA working group clinical practice guidelines 1.
Diagnostic Criteria
The diagnosis of ABPA should be suspected in patients with predisposing conditions or a compatible clinico-radiological presentation, and the following blood tests are essential for diagnosis:
- Total serum IgE: typically elevated above 500 IU/mL in ABPA, serves as both a diagnostic marker and a way to monitor treatment response 1
- Aspergillus-specific IgE: demonstrates sensitization to the fungus, with a cut-off value of ≥0.35 kUA·L−1 1
- Aspergillus-specific IgG: indicates an immune response to colonization, with population-specific cut-offs recommended 1
- Peripheral blood eosinophil count: reflects the allergic inflammatory response characteristic of ABPA, with a cut-off value of ≥500 cells·μL−1 1
Additional Supportive Tests
Additional supportive tests may include:
- Complete blood count with differential
- Comprehensive metabolic panel
- Pulmonary function tests
Importance of Timing
The blood tests should be collected before initiating corticosteroid therapy, as treatment may rapidly decrease IgE levels and eosinophil counts, potentially obscuring the diagnosis 1.
Diagnostic Algorithm
The revised ISHAM-ABPA working group clinical practice guidelines provide a diagnostic algorithm for ABPA, which includes the essential components of A. fumigatus-specific IgE and serum total IgE, as well as other components such as positive IgG against A. fumigatus, blood eosinophil count, and thin-section chest computed tomography consistent with ABPA 1.
From the Research
Blood Tests for Suspected Allergic Bronchopulmonary Aspergillosis (ABPA)
The following blood tests are recommended for suspected ABPA:
- Total serum IgE concentration 2, 3, 4, 5
- Precipitating serum antibodies to Aspergillus fumigatus 2, 6, 5
- Aspergillus fumigatus-specific IgE 3, 6
- Aspergillus fumigatus-specific IgG 6
- IgG antibody index to Aspergillus fumigatus 5
Rationale for Each Test
- Total serum IgE concentration: useful for monitoring treatment responses in ABPA 3
- Precipitating serum antibodies to Aspergillus fumigatus: important for diagnosis of ABPA 2, 6, 5
- Aspergillus fumigatus-specific IgE: has limited utility in monitoring treatment responses, but may be useful in diagnosis 3, 6
- Aspergillus fumigatus-specific IgG: extremely useful in diagnosis and differential diagnosis of ABPA, but unreliable in monitoring treatment response 6
- IgG antibody index to Aspergillus fumigatus: may be inconsistent, but important for diagnosis of ABPA 5