Diagnostic Criteria for NTM Pulmonary Disease According to the American Thoracic Society
According to the American Thoracic Society (ATS) and Infectious Diseases Society of America (IDSA), diagnosis of nontuberculous mycobacterial (NTM) pulmonary disease requires meeting specific clinical, radiographic, and microbiologic criteria, all of which are equally important and must be met to establish a diagnosis. 1
Minimum Evaluation Requirements
The minimum evaluation for suspected NTM pulmonary disease should include:
- Chest radiograph or, if no cavitation is present, high-resolution computed tomography (HRCT) scan 1
- Three or more sputum specimens for acid-fast bacilli (AFB) analysis 1
- Exclusion of other disorders such as tuberculosis and lung malignancy 1
Diagnostic Criteria
Clinical Criteria (both required)
- Pulmonary symptoms, nodular or cavitary opacities on chest radiograph, or HRCT scan showing multifocal bronchiectasis with multiple small nodules 1
- Appropriate exclusion of other diagnoses 1
Microbiologic Criteria (one of the following required)
- Positive culture results from at least two separate expectorated sputum samples 1
- Positive culture result from at least one bronchial wash or lavage 1
- Transbronchial or other lung biopsy with mycobacterial histopathologic features (granulomatous inflammation or AFB) and positive culture for NTM, or biopsy showing mycobacterial histopathologic features and one or more sputum or bronchial washings that are culture positive for NTM 1
Important Considerations
- Expert consultation should be obtained when NTM are recovered that are either infrequently encountered or usually represent environmental contamination 1
- Patients suspected of having NTM lung disease but who do not meet the diagnostic criteria should be followed until the diagnosis is firmly established or excluded 1
- Making the diagnosis of NTM lung disease does not automatically necessitate treatment initiation, which is a decision based on potential risks and benefits for individual patients 1
Laboratory Features
- The preferred staining procedure is the fluorochrome method 1
- Specimens should be cultured on both liquid and solid media 1
- NTM should generally be identified to the species level 1
- Methods of rapid species identification include commercial DNA probes and high-performance liquid chromatography (HPLC) 1
Application of Criteria
- These criteria fit best with Mycobacterium avium complex (MAC), M. kansasii, and M. abscessus 1
- There is insufficient knowledge about most other NTM species to be certain these diagnostic criteria are universally applicable 1
- Research shows that using only one or two of the criteria may significantly overestimate the number of NTM pulmonary disease cases, highlighting the importance of meeting all three criteria 2
Special Populations
For individuals with cystic fibrosis (CF), the ATS/IDSA criteria are recommended for diagnosing NTM pulmonary disease, although these criteria have not been specifically validated in CF patients 1.
Common Pitfalls
- Mistaking environmental contamination for true infection 1
- Initiating treatment based on a single positive culture 1, 2
- Failing to exclude tuberculosis, which often presents similarly 1
- Overlooking the heterogeneous clinical course of NTM pulmonary disease, which can range from stable disease not requiring treatment to refractory disease with significant morbidity and mortality 3
The application of these diagnostic criteria is essential for accurate diagnosis and appropriate management of NTM pulmonary disease, preventing both underdiagnosis with risk of disease progression and overdiagnosis leading to unnecessary treatment 2, 4.