Diagnostic Value of Microscopy, Galactomannan, and PCR in Aspergillus Culture-Positive BALF Samples: A Laboratory-Based Pilot Study.

Background: Diagnosing invasive aspergillosis (IA) remains challenging despite the availability of various tests due to the limited sensitivity and variability in accuracy depending on the clinical context. Laboratory-based definitions consider different mycological criteria, such as culture and galactomannan (GM) positivity, equivalent in diagnostic weight. However, a more detailed analysis is essential for reliably distinguishing true infection from colonisation.

Objectives: This laboratory-based pilot study aimed to evaluate the diagnostic reliability of culture positivity by comparing it with fungal microscopy, GM testing, and Aspergillus-specific PCR in bronchoalveolar lavage fluid (BALF) samples, all of which were culture-positive for Aspergillus.

Materials and methods: Ninety-two Aspergillus fumigatus culture-positive BALF specimens were obtained from mixed patient populations, displaying various risk factors for IA. The multi-assay approach used direct microscopy, GM, and Aspergillus-specific PCR. The diagnostic value of each test was assessed utilising a composite score based on mycological findings and clinical suspicion.

Results: Among 92 culture-positive BALF samples, positivity rates for microscopy, GM, and PCR were 12.0% (n = 11), 27.2% (n = 25), and 28.3% (n = 26), respectively. Notably, in 58.7% (n = 54) of cases, culture positivity was not supported by any other mycological test. Direct microscopy showed the strongest correlation with other diagnostic methods, whereas GM and PCR showed moderate agreement.

Conclusions: Based on our data, the current practice of weighing all mycological parameters equally should be reconsidered, with greater emphasis on microscopy and multimodal diagnostics rather than on culture alone, particularly in non-neutropenic patients.