Comparative performance of Aspergillus galactomannan ELISA and PCR in sputum from patients with ABPA and CPA

- Analysis of sputum galactomannan (GM) compared with PCR signal strength showed cut-off of 6.5 in the Aspergillus GM assay.
- A GMI of 6.5 was associated with approximately 50% of strongly positive PCR values.
- Sputum characteristics could be used as good predictor of GMI values and PCR signal.
- The utility of GM in sputum for diagnosis or for following therapy is unclear.

ObjectivesGalactomannan (GM) and Aspergillus DNA detection are useful tools for the diagnosis of invasive pulmonary aspergillosis (IPA), primarily in blood and bronchoscopy samples. This study aimed to evaluate the utility of both markers for detection of Aspergillus in sputum from patients with allergic bronchopulmonary aspergillosis (ABPA) and chronic pulmonary aspergillosis (CPA).MethodsABPA or CPA demographic patient data were retrieved. This retrospective observational audit included 159 patients with at least one sputum pair. 223 sputum sample pairs were analysed, as well as six control samples for GM only. Real time PCR was performed following sputum DNA extraction using the MycAssay™ Aspergillus kit and cycle thresholds were subtracted from 38 to give positive values (transformed Ct, TCt).ResultsThe mean age of the patients was 61.81 years (SD: ± 11.06; range 29-100). One hundred and twenty-six (79.2%) had CPA. Cultures were positive for fungi in 13.1% of the samples, and A. fumigatus was the commonest (11.9%) fungus isolated. Receiver operating characteristic (ROC curve) analysis of sputum GM comparing TCt of > 0.0, and > 2.0 to derive GMI cut-off values showed a cut-off of 6.5. About 50% of sputa with strongly positive PCR values had GM values > 6.5. Two of six (33%) control samples had GM indices > 6.5.ConclusionIt is not clear that GM determinations in sputum are useful for diagnosis of either CPA or ABPA, or following therapy.