Galactomannan detection in sputum samples of patients with chronic obstructive pulmonary disease: A promising marker for diagnosis of chronic pulmonary aspergillosis?

Background and purpose

Diagnosing chronic pulmonary aspergillosis (CPA) is challenging due to nonspecific symptoms, variable radiological findings, and limited mycological evidences. While galactomannan (GM) testing has been validated in serum and bronchoalveolar lavage fluid (BAL) for invasive pulmonary aspergillosis (IPA), its usefulness in sputum samples for CPA remains unclear. This study aimed to determine an appropriate GM cut-off level in sputum samples and its performance in diagnosis of CPA.

Materials and methods

The diagnostic performance of sputum GM was evaluated in patients with COPD suspected of having CPA referred to the two reference centers for pulmonary diseases in Iran, and compared against established diagnostic criteria, including Aspergillus culture and IgG antibody tests. The sensitivity, specificity and positive and negative predictive value for sputum GM test were calculated. The optimal cut-off for sputum GM was determined by receiver operating characteristic (ROC).

Results

Of 196 COPD patients, 189 were analyzed for sputum GM. Sputum GM demonstrated an area under the receiver operating characteristic curve (AUC) of 0.83 (with 95 % confidence intervals (CI) of 0.748 – 0.913 and a p-value < 0.001). The optimal cut-off value for the sputum GM index was 1.44. The sensitivity and specificity were found to be 83.3 % and 74.2 % respectively. The median (IQR) levels of sputum GM index were significantly higher in CPA patients compared to non-CPA patients. (Pv <0.001).

Conclusions

Overall, our findings suggest that sputum GM is a valuable tool in the diagnosis of CPA; however, further prospective validation is warranted to increase its clinical utility.