Aspergillus-Antigen Testing:Introduction, Principle, Clinical Significance, and Keynotes

Introduction

Aspergillus species, particularly Aspergillus fumigatus, are major causes of invasive aspergillosis (IA), especially in immunocompromised patients, such as those with hematological malignancies, transplant recipients, or those with prolonged neutropenia. Diagnosis of IA is often challenging because clinical symptoms and radiological findings are nonspecific. Aspergillus antigen testing, mainly targeting galactomannan (GM) and (1→3)-β-D-glucan (BDG), has become a cornerstone in early, non-culture-based detection of invasive aspergillosis.

Principle

• Galactomannan Antigen Test (GM):
  • Detects galactomannan, a polysaccharide cell wall component released during active growth of Aspergillus.
  • Performed using an enzyme immunoassay (EIA/ELISA) method.
  • Detects antigen in serum, bronchoalveolar lavage (BAL) fluid, and sometimes cerebrospinal fluid (CSF).
• (1→3)-β-D-Glucan (BDG) Test:
  • Detects a pan-fungal cell wall component (not specific to Aspergillus).
  • Useful as a supportive test but less specific, since it may be positive in other invasive fungal infections.

Clinical Significance

• Early Diagnosis: Enables the detection of invasive aspergillosis before positive cultures, thereby improving survival rates.
• Screening & Monitoring: Recommended in high-risk patients (e.g., hematology/oncology, transplant) for surveillance and treatment monitoring.
• BAL vs Serum: BAL galactomannan is often more sensitive than serum testing, especially in pulmonary aspergillosis.
• Treatment Guidance: Rising antigen levels may indicate treatment failure, while declining levels suggest response to therapy.
• Limitations:
  • False positives may occur due to certain antibiotics (piperacillin-tazobactam), dietary sources, or cross-reactivity with other fungi (Penicillium, Fusarium).
  • False negatives may occur in patients receiving antifungal prophylaxis.

Keynotes

• Galactomannan antigen testing is a valuable non-invasive diagnostic tool for invasive aspergillosis.
• Serum and BAL specimens are most commonly used; BAL provides higher sensitivity.
• BDG testing supports diagnosis but lacks specificity for Aspergillus.
• Best interpreted in combination with clinical, radiological, and mycological evidence (per EORTC/MSG criteria).
• Antigen kinetics can help in treatment monitoring and prognosis assessment.
• Remains a critical part of diagnostic algorithms for immunocompromised and critically ill patients.

Further Readings

1. https://www.euroimmun.com/fileadmin/user_upload/News/Professional-articles/Aspergillus_MedLab_Issue_3-19.pdf
2. https://www.mayocliniclabs.com/test-catalog/overview/84356
3. https://www.journalofinfection.com/article/S0163-4453(24)00093-8/fulltext
4. https://pmc.ncbi.nlm.nih.gov/articles/PMC5483917/
5. https://www.eurofins-viracor.com/test-menu/1600-aspergillus-galactomannan-eia/
6. https://www.journalofinfection.com/article/S0163-4453(24)00093-8/fulltext
7. https://www.fda.gov/files/drugs/published/Guidance-on-Qualification-of-Biomarker-%E2%80%94-Galactomannan-in-studies-of-treatments-of-invasive-Aspergillosis.pdf
8. https://www.leedsth.nhs.uk/services/pathology/tests/aspergillus-antigen/
9. http://www.bordier.ch/ASP-025/266-REC-IFU-FungaDia-Aspergillus-EN_Rev4-22.pdf
10. https://www.sciencedirect.com/science/article/pii/S0163445314000097
11. https://miravistavets.com/fungal-diseases/aspergillus/false-positives-asper-antigen-test/
12. https://www.mayocliniclabs.com/test-catalog/download-setup?format=pdf&unit_code=84356
13. http://www.bordier.ch/ASPE-096/266-REC-IFU-FungaDia-Aspergillus_ELISA-EN_Rev6-23.pdf
14. https://commerce.bio-rad.com/webroot/web/pdf/inserts/CDG/en/62794_881115_EN.pdf