Abstract In recent years, the number of patients with non-tuberculous mycobacterial pulmonary disease (NTM-PD) has increased worldwide. The most common causal agent of NTM-PD is the Mycobacterium avium-complex (MAC) and defined as MAC pulmonary disease (MAC-PD).The diagnosis of MAC-PD requires MAC isolation, but there are many cases where it is not separated by sputum mycobacterial testing. We often wonder whether to watchful waiting or not . In Japan, the serum anti- GPL-core IgA antibody test can be measured. It uses the ELISA method to measure IgA antibodies against the major Glycopeptidolipid (GPL)-core antigen, which constitutes the cell wall, in serum and used as an adjunctive diagnostic tool for MAC-PDWe examined whether the serum anti- GPL-core IgA antibody test could be a factor in determining whether watful waiting or not. We measured the serum anti- GPL-core IgA antibody test in patients who suspected MAC-PD in our hospital between Apr 2021 and May 2025. The results were divided into positive and negative groups. The negative group was placed under observation.In the positive group, we diagnosed MAC-PD by positive culture result from acid-fast bacilli (AFB) analysis in sputum tests or bronchial washing. In the positive group, cases in which AFB were not detected were categorized as ‘watchful waiting’. Of the 1,798 cases suspected of NTM-PD for which serum anti-GPL-core IgA antibodies were measured, a positive result was assigned to those with levels of 0.7 U/mL or higher. and MAC-PD was suspected, 502 (27.9%) were positive and 1,296 (72.1%) were negative. Of the positive cases, 246 (49%) showed AFB isolation from sputum or bronchial washing, with a median serum anti-GPL-core IgA antibody level of 6.3 U/mL (0.7-10.0 U/mL). Other species isolated included Mycobacterium gordonae, kansasii, abscessus, fortuitum, goodie, and porcinum. In contrast, of the positive cases, 256 (51%) did not show AFB isolation, with a median level of 2.1 U/mL (0.7-10.0 U/mL). Higher levels of serum anti-GPL-core IgA antibodies measured in suspected patients of having MAC-PD correlated with a higher proportion of culture-positive cases. Lower values indicated that fewer patients were shedding bacteria, suggesting the potential for categorization into watchful waiting groups.However, limitations included the fact that the study was single-center that the serum anti- GPL-core IgA antibody test is only used for diagnose MAC-PD only in JAPAN, and that there is a possibility of false positives from non-MAC bacteria, necessitating culture confirmation wherever possible. This abstract is funded by: None
Takeda et al. (Fri,) studied this question.