Aspergillus Antibody (IgG) & Aspergillus Antigen (Galactomannan) Tests
🧫 Aspergillus Antibody (IgG) & Aspergillus Antigen (Galactomannan) Tests: Complete Guide
Essential immunologic and antigen assays for diagnosing invasive and chronic pulmonary aspergillosis
1. What Is Aspergillus?
Aspergillus is a ubiquitous environmental mold, with A. fumigatus, A. flavus, and A. niger being the most clinically relevant species.
While harmless to healthy individuals, it can cause infection or hypersensitivity in:
- Immunocompromised patients (hematologic malignancy, long-term steroids, transplant recipients)
- Patients with underlying lung disease (post-TB cavities, COPD, bronchiectasis, asthma)
- Those on prolonged antibiotic or steroid therapy
Major clinical syndromes
- Invasive Pulmonary Aspergillosis (IPA)
- Chronic Pulmonary Aspergillosis (CPA)
- Allergic Bronchopulmonary Aspergillosis (ABPA)
2. Overview of Test Types
| Test | Meaning | Primary Diagnostic Use |
|---|---|---|
| Aspergillus IgG Antibody | Host antibody response | CPA, aspergilloma, ABPA assessment |
| Aspergillus Antigen (Galactomannan) | Cell-wall antigen released during fungal growth | Early detection of IPA, monitoring high-risk patients |
3. Clinical Indications
✔ Aspergillus IgG Antibody
- Diagnosis of Chronic Pulmonary Aspergillosis (CPA)
- Detection of aspergilloma (fungal ball)
- Evaluation of ABPA
- Assessment of suspected Aspergillus infection in structural lung disease
✔ Aspergillus Antigen (Galactomannan)
- Early diagnosis of Invasive Pulmonary Aspergillosis (IPA)
- Monitoring high-risk groups:
- Hematologic malignancy, stem cell transplant, solid organ transplant
- Prolonged neutropenia
- ICU patients with uncontrolled lung infection
- BAL (bronchoalveolar lavage) testing provides the highest sensitivity
4. Test Methods
✔ FEIA (Fluorescent Enzyme Immunoassay)
- Detects IgG antibodies or galactomannan via fluorescent enzyme reaction
- High sensitivity and compatible with automated systems
- Frequently performed on ImmunoCAP/Phadia platforms
✔ EIA / ELISA (Enzyme Immunoassay)
- Measures colorimetric change from enzyme–substrate reaction
- Widely used for both IgG and antigen assays
- Capable of detecting low levels of antigen/antibody
- BAL specimens markedly improve sensitivity for diagnosing IPA
5. Reference Ranges
✔ Aspergillus IgG Antibody
Varies by manufacturer
- < 40 mg/L: Negative
✔ Aspergillus Antigen (Galactomannan)
- Index < 0.5: Negative
- Index ≥ 0.5 or ≥ 1.0: Positive (laboratory thresholds vary)
BAL galactomannan: higher diagnostic accuracy than serum
6. Clinical Significance
A. When Aspergillus IgG Is Elevated
Indicates chronic or ongoing infection, not just previous exposure.
Associated conditions:
- Chronic Pulmonary Aspergillosis (CPA)
- Cavities, fungal balls, chronic cough, hemoptysis, weight loss
- Aspergilloma
- ABPA (in some cases)
- Post-tuberculosis lung disease with superimposed Aspergillus infection
➡ IgG elevation strongly supports active chronic infection, especially when CT shows cavities.
B. When Aspergillus Antigen (Galactomannan) Is Positive
Reflects active invasion and circulating fungal antigen.
Most common in:
- Hematologic malignancy during neutropenia
- Stem cell or solid organ transplant recipients
- High-dose corticosteroid users
- Severe or persistent pulmonary infection
- BAL positivity has the highest diagnostic value
➡ Essential tool for early detection of IPA.
7. Interpretation Considerations
✔ 1) Interpreting Aspergillus IgG
- Previous environmental exposure is common → IgG alone does not prove disease
- Must always correlate with:
- Clinical symptoms
- CT findings (cavities, nodules, pleural thickening)
- Immunocompromised patients may not produce IgG → normal result does not exclude infection
✔ 2) Interpreting Galactomannan Antigen
🔸 False Positives
- Piperacillin–tazobactam, amoxicillin-clavulanate
- Grain-based foods, cereals (contain galactomannan)
- Bifidobacterium infection
- Other fungal infections
- Dilution issues in BAL samples
🔸 False Negatives
- Prior or prophylactic antifungal therapy (especially mold-active azoles)
- Localized infections without significant antigen release
8. Summary Table
| Test | What It Indicates | Main Use |
|---|---|---|
| Aspergillus IgG | Chronic infection | CPA, aspergilloma |
| Galactomannan Antigen | Active invasion, circulating antigen | IPA |
9. Key Takeaways
- Aspergillus IgG is essential for diagnosing CPA
- Galactomannan antigen is crucial for early detection of IPA
- FEIA/ELISA assays allow reliable, automated quantification
- Always consider false positive/negative factors
- Combine with CT imaging, BAL testing, and clinical context for accurate diagnosis
📚 References
- UpToDate: Diagnosis of Invasive Aspergillosis
- Clinical Microbiology Reviews: Chronic Pulmonary Aspergillosis
- IDSA Clinical Practice Guidelines for Aspergillosis
- Tietz Textbook of Clinical Chemistry and Molecular Diagnostics, 6th ed.
- Patterson TF, et al. IDSA Aspergillosis Guidelines (2016)
- Mayo Clinic Laboratories: Aspergillus IgG & Galactomannan Assays