Aspergillus (Galactomannan) Antigen, Serum (MayoID: ASPAG)

Aspergillus has a predilection to invade and obstruct blood vessels, resulting in tissue infarction and hemorrhage. Invasive aspergillosis (IA) is primarily a life-threatening infection with prolonged and profound neutropenia. Patients with acute leukemia and recipients of allogeneic hematopoietic stem cell transplantation are especially at risk.

Early diagnosis is difficult in this clinical setting, and crude mortality of >90% is common. Culture lacks sensitivity in both blood and sputum. High-resolution computed tomographic scans of the chest are usually nonspecific but can be highly suggestive in neutropenic patients.

The Aspergillus antigen, galactomannan, has been detected in the serum, urine, and BAL from patients with IA using a commercially-available sandwich ELISA. This assay has a reported sensitivity of 67-100% and a specificity of 81-99% when performed on sera from patients receiving treatment for hematological malignancies. However, the assay is prone to false positive results due to common antibiotic use or other fungal species. The selection of high-risk patients is critical for minimizing false-positive tests and having a high positive predictive value.

• False positives can be seen in patients receiving Piperacillin/Tazobactam and Amoxicillin/Clavulanic acid, or colonized by other invasive mycoses (e.g., penicilliosis, histoplasmosis, and blastomycosis).
• Antifungal therapy may cause falsely negative results.

• Galactomannan is only recommended as a diagnostic test for invasive aspergillosis in patients with a consistent clinical presentation.
• Minimize false positives by reserving testing for those at the highest risk.

1. Patterson TF, Thompson GR 3rd, Denning DW, Fishman JA, Hadley S, Herbrecht R, Kontoyiannis DP, Marr KA, Morrison VA, Nguyen MH, Segal BH, Steinbach WJ, Stevens DA, Walsh TJ, Wingard JR, Young JA, Bennett JE. Practice Guidelines for the Diagnosis and Management of Aspergillosis: 2016 Update by the Infectious Diseases Society of America. Clin Infect Dis. 2016; 15:63(4):e1-e60. Epub 2016 Jun 29.