Evaluation of combination anti-glycopepidolipid-core IgA antibody levels and chest CT findings to diagnose Mycobacterium avium complex pulmonary disease

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Background: Mycobacterium avium complex (MAC) pulmonary disease (PD) is diagnosed based on the criteria outlined in the 2020 American Thoracic Society (ATS) Clinical Practice Guidelines. However, meeting bacteriological criteria can be challenging, particularly in patients who do not produce sputum. Aim: To evaluate the diagnostic utility of combining serological testing for anti-glycopeptidolipid-core IgA antibody (MAC antibody) with chest computed tomography (CT) findings, specifically nodular bronchiectatic (NB) and fibrocavitary (FC) disease, for diagnosing MAC-PD. Methods: This retrospective study included patients who underwent both MAC antibody testing and chest CT imaging at the Respiratory Medicine, Kita-harima Medical Center, Japan, between October 1, 2023, and September 30, 2024. Additionally, the acid-fast bacilli culture results were analyzed. The cutoff value for MAC antibody was set at 0.7. Results: Of 121 patients, eight were diagnosed with MAC-PD based on the ATS guidelines. Sixty-two patients were diagnosed with other pulmonary diseases. The combination of NB- or FC-type CT findings with MAC antibody testing demonstrated a sensitivity of 62.5% and specificity of 96.7% for diagnosing MAC-PD. Two cases with false-positive results were identified as other Mycobacterium species. Conclusion: Although the combination of CT and MAC antibody testing is a highly specific diagnostic tool for MAC-PD, cross-reactivity with other acid-fast bacilli remains a limitation. Therefore, confirming at least one positive MAC culture, as temporarily determined by the new Japanese guidelines may enhance diagnostic specificity.

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