A febrile neutropenic patient receiving piperacillin-tazobactam has two consecutive serum galactomannan indices of 1.2 and 1.5. HRCT chest shows no nodules, halo signs or cavitation, and the patient is clinically stable. What is the most likely explanation for the elevated galactomannan?
- A Early invasive pulmonary aspergillosis before CT changes appear
- B False-positive reaction caused by the beta-lactam antibiotic ✓
- C Airway colonisation by Aspergillus awaiting invasion
- D Disseminated cryptcoccal infection with negative CrAg
Correct answer: B. False-positive reaction caused by the beta-lactam antibiotic
Explanation
Piperacillin-tazobactam and amoxicillin-clavulanate contain galactomannan-like epitopes derived from Penicillium used in their manufacture and are well documented causes of false-positive serum galactomannan, particularly in patients with low fungal risk. Absence of any compatible HRCT finding supports a spurious result rather than probable invasive aspergillosis. Colonisation alone rarely drives sustained serum indices above 1.0, and Cryptococcus classically gives a false-negative galactomannan with a positive CrAg.
Reference: Mandell, Douglas and Bennett's Principles and Practice of Infectious Diseases, 9th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.