Increasing sputum samples for testing improves diagnostic yield of Mycobacterium avium complex pulmonary disease

In Mycobacterium avium complex pulmonary disease (MAC-PD), diagnosis requires a positive culture from at least two separate expectorated sputum specimens. The optimal number of sputum examinations remains unclear.

This study sought to elucidate the diagnostic yield of acid-fast bacilli in MAC-PD using 3 sputum specimens and to clarify the clinical characteristics of patients with MAC-PD diagnosed using 3 sputum specimens. Furthermore, we investigated the correlation between increased number of sputum specimens and diagnostic yield.

They reviewed the medical records of 139 patients with MAC-PD diagnosed at Toho University Omori Medical Center for whom at least three sputum specimens were examined before treatment from November 2014 through June 2021. Patients were classified into the 3-sputum diagnosed and the non-3 sputum diagnosed groups based on diagnostic procedure; clinical and radiological characteristics were compared. We also assessed diagnostic yield with the increased number of sputum specimens.

Results

Diagnostic yield with 3 sputum specimens was 16.5% (23/139).

The 3-sputum diagnosed group had a lower body mass index including cavitary lesions compared with the non-3 sputum diagnosed group.

When the number of sputum specimens was increased to 6, the diagnostic yield increased to 23.7% (33/139).

Diagnostic yield with 3 sputum specimens was 16.5%. Patients diagnosed using 3 sputum specimens had more severe chest CT findings including cavitary lesions. Increasing the number of sputum specimens to 6 improved diagnostic yield by 7.2%. In MAC-PD, increasing the number of sputum specimens to 6 is plausible for a definitive diagnosis

Reference:

Urabe, N., Sakamoto, S., Masuoka, M. et al. Efficacy of three sputum specimens for the diagnosis of Mycobacterium avium complex pulmonary disease. BMC Pulm Med 23, 29 (2023). https://doi.org/10.1186/s12890-023-02327-5