Clinical scenario: persistent fever & cough | pulmonary TB suspicion
A 2-year-old child presents with persistent fever, cough, and poor weight gain for 2 months. His father was recently diagnosed with smear-positive pulmonary tuberculosis. Chest X-ray shows right hilar lymphadenopathy with a focal opacity in the right upper lobe. The child is unable to produce an adequate sputum sample despite attempts at induction.
The clinician wants to perform GeneXpert MTB/RIF testing for microbiological confirmation of tuberculosis.
Which is the most appropriate alternative specimen for GeneXpert testing in this child?
A. Blood sample
B. Stool sample
C. Urine sample
D. Nasopharyngeal swab
E. Pleural fluid
Correct answer & Explanatin:
Correct answer: B. Stool sample
Explanation:
Young children often cannot expectorate sputum. Stool is an accepted alternative specimen for detection of Mycobacterium tuberculosis using GeneXpert MTB/RIF, particularly in children with suspected pulmonary TB.
The child swallows respiratory secretions containing bacilli, which can then be detected in stool using molecular testing.
Why other options are incorrect:
- A. Blood sample: Not routinely used for diagnosing pulmonary TB.
- C. Urine sample: Useful mainly for disseminated TB in selected situations (e.g., urine LAM in immunocompromised patients), not routine pulmonary TB diagnosis.
- D. Nasopharyngeal swab: Not a standard specimen for GeneXpert diagnosis of pulmonary TB.
- E. Pleural fluid: Used when pleural TB is suspected, not in isolated pulmonary disease.
Exam pearl: In children unable to produce sputum, samples for TB testing may include:
- Induced sputum
- Gastric aspirate/lavage
- Stool (GeneXpert MTB/RIF)
