Serum carbohydrate antigen 19-9 (CA19-9) levels can increase in nontuberculous mycobacteria pulmonary disease (NTM-PD) and the levels correlate with disease activity. We compared the clinical characteristics of NTM-PD patients with and without elevated CA19-9 levels and evaluated its association with the antibiotic response in a retrospective study of NTM-PD patients diagnosed between January 1994 and December 2020. We analyzed 1,112 patients who had serum CA19-9 measured: 322 with elevated CA19-9 and 790 with normal CA19-9. The erythrocyte sedimentation rate and C-reactive protein levels were significantly higher in the elevated CA19-9 group (p < 0.001 and p = 0.029, respectively). The 1-year culture conversion rate after antibiotics did not differ between the elevated (n = 206) and normal (n = 377) CA19-9 groups (80% vs. 72%, p = 0.055). Analysis of a subset of 434 patients revealed that current smoking, bronchiectasis, acid-fast bacilli smear positivity, and the M. abscessus strain significantly reduced microbiological cure rates. Serum CA 19-9 levels did not have a significant association with microbiological cure in a multivariate analysis. These findings suggest that the role of serum CA19-9 in predicting antibiotic treatment outcomes is limited, and that elevated CA19-9 does not necessarily indicate a poor outcome.

Few clinical factors can help predict spontaneous culture conversion (SCC) in patients with Mycobacterium avium complex-pulmonary disease (MAC-PD). We retrospectively classified 373 MPD patients who had undergone watchful waiting without antibiotics according to the so-called ‘body mass index (BMI), age, cavity, erythrocyte sedimentation rate (ESR), and sex (BACES)’ severity. We evaluated whether lower severity is associated with a higher rate of SCC. Of 373 patients, 153 (41%) achieved SCC without antibiotics during a median follow-up of 48.1 months. There was a trend toward a higher SCC rate in patients with lower BACES severity: 48% (87/183), 37% (58/157), and 24% (8/33) in the mild, moderate, and severe BACES groups, respectively. In addition, a favorable outcome, defined as maintaining SCC or having two consecutive negative sputum cultures until the last follow-up date, was also more common in patients with lower BACES severity with 53% (97/183), 34% (54/157), and 18% (6/33) in the mild, moderate, and severe BACES groups, respectively. In multivariate analysis, moderate (hazard ratio [HR]=0.63; 95% confidence interval [CI] 0.44 – 0.91; p = 0.013) and severe BACES (HR 0.37; 95% CI 0.16 – 0.90; p = 0.028) had a significantly negative impact on favorable outcomes compared to mild BACES. Lower BACES severity may be associated with SCC in MAC-PD patients.