Laboratory findings of NTM

AFB Smear and NAAT Test (LPA/CBNAAT/TRUENAT)

  • Two specimens are to be collected: One must be a morning specimen and sent for AFB Smear. Induction of sputum with hypertonic saline may be used in patients who are unable to produce sputum spontaneously.
  • If a smear-positive (AFB-positive) specimen shows results for M.TB but is not detected by NAAT technology, the specimen should be inoculated for LC/LJ culture to check the presence of NTM. 
  • NAAT (LPA/CBNAAT/TRUENAT) detect only M. TB Complex ……..NOT NTM.

 

Clinical and radiographic manifestations

  • The symptoms are often nonspecific, such as chronic cough, increased sputum production, dyspnoea, low-grade fever, malaise, and weight loss, and overlap clinical characteristics with pulmonary TB.

  • Radiological imaging is important when NTM lung disease is suspected. The broad range of radiological patterns seen in NTM lung disease includes bronchiectasis, nodular lesions, cavitary lesions, and parenchymal consolidation. 

Diagnosis of NTM Lung Disease

The clinician must integrate clinical, radiographic, and microbiological data to make a diagnosis of NTM lung disease, but it can be confirmed by 


• At least two positive cultures from sputum. 
• One positive culture in the case of bronchoscopic wash or lavage, or 
• A transbronchial or other lung biopsies with a positive culture for NTM or compatible histopathological features such as granulomatous inflammation or stainable acid-fast bacilli (AFB). 

Presumptive NTM

The symptoms of cases of Non-Tuberculosis Mycobacteria (NTM) overlap with that of Tuberculosis and are nonspecific. These include chronic cough, increased sputum production, dyspnoea, low-grade fever, malaise, and weight loss. Hence presumptive NTM cases are identified as:

  • discrepancies between microscopy and molecular tests (AFB Smear Positive but NAAT/ LPA negative).
  • Culture is positive, but MPT 64 is negative.
  • Cases that do not respond to ATT
     
Subscribe to