Diagnostic Tools Used in Non-tuberculous Mycobacterial [NTM] Infection

Diagnosis of Non-tuberculous Mycobacteria (NTM) will be based on:

1. Tests to show the presence of NTM bacteria 
2. Clinical judgement based on clinical symptoms

Diagnosing NTM lung disease takes a series of steps, first to rule out other possible causes for the illness and then to confirm that the patient has been infected with NTM. 

Usually, for NTM confirmation, patients are thoroughly examined clinically,  and a detailed medical history is taken. This is followed by a minimum of three distinct types of evaluations:

• Chest X-ray or, in the absence of cavitation, chest High Resolution Computerized Tomography (HRCT) scans to look for nodules, cavities or other changes in the lung tissue and airways indicating NTM disease.
• Lab cultures to confirm NTM infection. Sputum sample will be collected for the cultures and as NTM is so common in the environment, to reduce the chance of a false positive, repeated for three or more sputum specimens for acid-fast bacilli analysis and sputum cultures will be prescribed. At times, sputum induction and bronchoscopy may be advised.
• Exclusion of other disorders such as TB and lung malignancy. In most patients, a diagnosis can be made without bronchoscopy or lung biopsy.

NTM lung disease is generally slowly progressive (relative to TB). There is usually sufficient time to collect adequate clinical material, specifically, multiple respiratory specimens necessary for making a diagnosis. 

For patients in whom the diagnosis is unclear, expert consultation should be sought. 

Resources

• American Thoracic Society Documents - NTM Diagnosis.

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