Can a Positive Anti-Mycobacterium avium Complex Antibody Test Predict NTM-PD?

Anti-Mycobacterium avium complex antibodies do not necessarily indicate the presence of MAC or of nontuberculous mycobacterial pulmonary disease.

Anti-Mycobacterium avium complex (MAC) antibody testing and clinical information obtained in routine practice may be used to estimate possible nontuberculous mycobacterial pulmonary disease (NTM-PD); however, per current guidelines, sputum samples or bronchoscopic examination are needed to confirm diagnosis, according to study findings published in Therapeutic Advances in Respiratory Disease.

Given that is it not currently possible to diagnose NTM-PD on the basis of anti-MAC antibodies alone, researchers assessed the efficacy of using a combination of anti-MAC antibodies and clinical findings to identify NTM-PD. Toward that end, the researchers conducted a retrospective, cross-sectional study at Showa University Fujigaoka Hospital in Yokohama, Kanagawa, Japan, between November 2017 and March 2021.

The researchers administered anti-MAC antibody tests — using a serum immunoglobulin A (IgA) antibody against the glycopeptidolipid (GPL) core and an enzyme-linked immunosorbent assay kit — to 938 patients with suspected NTM-PD on the basis of the clinical findings and imaging studies. Anti-MAC antibodies were found in 30.5% (286/938) of participants.

Notably, the latest criteria for diagnosing NTM-PD from the American Thoracic Society and the Infectious Diseases Society of America require at least 2 positive sputum cultures of the same species or a single positive culture from a specimen obtained from bronchoscopy. Accordingly, sputum samples were obtained from all participants at least 2 times weekly, whenever possible. Polymerase chain reaction tests were performed as well, to identify MAC and M tuberculosis.

Anti-MAC antibodies can be positive in patients not harboring MAC and in patients with multiple mycobacterial infections; thus, extra attention is warranted when diagnosing pulmonary disease caused by MAC in patients with a positive antibody test result.

The participants (596/938 women) ranged in age from 15 to 95 years; their body mass index (BMI) ranged from 10.9 to 31.8 kg/m2; and 672/938 had never smoked. 

Results of the study showed that NTM-PD was identified in 19.6% (184 of 938) of the participants. Of these 184 participants, 76.6% (141) had tested positive for anti-MAC antibodies; however, among the 754 participants who were not definitively diagnosed with NTM-PD, 19.2% (145) had tested positive for anti-MAC antibodies.

Per multivariable analysis, factors significantly associated with NTM-PD at diagnosis were positive anti-MAC antibodies (odds ratio [OR], 12.4183; 95% CI, 8.1102-19.0148; P <.0001); low BMI (OR, 0.9096; 95% CI, 0.8502-0.9711; P =.0051); absence of malignancy (OR, 0.5562; 95% CI, 0.3189-0.9699; P =.0387); and presence of cavity-forming lung lesions (OR, 2.9537; 95% CI, 1.4881-5.8625; P =.002).

Several limitations of the current study warrant mention. Because the study was conducted at a single facility, the generalizability of results may be limited. Further, because of the retrospective nature of the study, the immunologic and genetic statuses of the participants were not analyzed.

 “Anti-MAC antibodies can be positive in patients not harboring MAC and in patients with multiple mycobacterial infections; thus, extra attention is warranted when diagnosing pulmonary disease caused by MAC in patients with a positive antibody test result,” said study authors. They concluded that “anti-MAC antibody testing and clinical factors obtained in routine practice could be used to estimate NTM-PD,” and that bronchoscopic examination is indicated for “patients with anti-MAC antibody positivity, low BMI, absence of malignancy, and presence of a cavity-forming lung lesion.”

References:

Iwasaki T, Yamaguchi F, Hayashi M, et al. Combination of anti-glycopeptidolipid-core IgA antibody and clinical features for diagnosing potential nontuberculous mycobacterium pulmonary disease in routine practice. Ther Adv Respir Dis.
2022;16:1-13. doi:10.1177/17534666221138002