Dear Editor,
We read the interesting article by de Oliveira etĀ al. on the performance of various investigations for diagnosing chronic pulmonary aspergillosis (CPA).1 The authors conclude that the diagnostic performance of the currently available tests is poor. Unfortunately, the authors have not measured serum Aspergillus fumigatus-specific IgG in their cohort by other more sensitive methods. Previous studies have demonstrated that detection of IgG antibodies by immunoassays is more sensitive than by immunoprecipitation methods (double immunodiffusion [DID] method or counterimmunoelectrophoresis [CIE] method).2ā4 We found that for every six tests done with the DID method, one additional diagnosis of allergic bronchopulmonary aspergillosis (ABPA) was secured when A.fumigatus-IgG was detected using the immunoassay. Notably, it is not clear against which reference standard the authors compared the performance of the index test (DID, CIE, serum or bronchoalveolar lavage fluid galactomannan index [GMI], or histopathology). For example, if DID or CIE was used to diagnose CPA, how could the performance of DID or CIE be assessed?5 The authors found histology to have a sensitivity of 78%. To our understanding, histology is the current reference standard and should be able to diagnose CPA in all cases. Finally, a receiver operating curve analysis was not performed to ascertain the diagnostic performance of the tests evaluated in the current study. The cut-off values of serum and BALF GMI used by the authors may not have been correct. In a recent prospective study, we found that serum and BALF GMI had the best sensitivities at cut-offs of 0.6 and 1.4, respectively, for diagnosing CPA.6 Importantly, we diagnosed CPA using a composite of clinical, radiological, and microbiological (culture positivity for aspergillus in respiratory secretions or A.fumigatus-specific IgG [fluorescent enzyme immunoassay method, FEIA]) assessments.6 Future studies should use either point-of-care tests or automated methods to detect A.fumigatus-specific IgG and should also develop cut-off values specific to their population.7
REFERENCES
- 1.ā
de Oliveira VF , Viana JA , Sawamura MVY , Magri ASGK , Nathan Costa A , Abdala E , Mariani AW , Benard G , Chaves Magri MM , 2023. Sensitivity of antigen, serology, and microbiology assays for diagnosis of the subtypes of chronic pulmonary aspergillosis at a teaching hospital in SĆ£o Paulo, Brazil. Am J Trop Med Hyg 108: 22ā26.
- 2.ā
Sehgal IS , Choudhary H , Dhooria S , Aggarwal AN , Garg M , Chakrabarti A , Agarwal R , 2018. Diagnostic cut-off of Aspergillus fumigatus-specific IgG in the diagnosis of chronic pulmonary aspergillosis. Mycoses 61: 770ā776.
- 3.ā
Sehgal IS , Dhooria S , Choudhary H , Aggarwal AN , Garg M , Chakrabarti A , Agarwal R , 2019. Efficiency of A fumigatus-specific IgG and galactomannan testing in the diagnosis of simple aspergilloma. Mycoses 62: 1108ā1115.
- 4.ā
Page ID , Richardson MD , Denning DW , 2016. Comparison of six Aspergillus-specific IgG assays for the diagnosis of chronic pulmonary aspergillosis (CPA). J Infect 72: 240ā249.
- 5.ā
Arora K , Muthu V , Aggarwal AN , Agarwal R , 2021. Can a test being evaluated in a study be itself used as a reference standard? Chest 159: 448.
- 6.ā
Sehgal IS , Dhooria S , Choudhary H , Aggarwal AN , Garg M , Chakrabarti A , Agarwal R , 2019. Utility of serum and bronchoalveolar lavage fluid galactomannan in diagnosis of chronic pulmonary aspergillosis. J Clin Microbiol 57: e01821ā18.
- 7.ā
Sehgal IS , Dhooria S , Soundappan K , Rudramurthy SM , Chakrabarti A , Agarwal R , 2023. Comparison of three sample types for performing LDBio Aspergillus immunochromatographic technology lateral flow assay for IgG/IgM antibody detection in chronic aspergillosis. Clin Microbial Infect 29: 404ā405.