Mycobacteria Practice Question

A 5 year old male patient develops low grade fevers; blood cultures are negative for bacterial and fungal growth, and imaging is suspicious for pulmonary TB. Which of the following should be collected first for TB culture?

Show Answer and Explanations

Gastric lavage — Correct answer

Correct. Gastric lavage is the preferred specimen to culture for Mycobacterium tuberculosis in children because they frequently cannot produce adequate sputum. It is performed in the morning before breakfast. After collection, it must be neutralized with an alkaline substance such as sodium bicarbonate or sodium hydroxide.

Midstream urine

Incorrect. Urine catch should be performed midstream, and in the morning. It is not done for culture unless the urinary system is suspected of infection. Urine can be assayed for mycobacterial lipoarabinomannan (LAM) and urine mycobacterial DNA, however.

Peripheral blood

Incorrect. Blood culture is only useful if there is mycobacteremia, and is not routinely performed. QuantiFERON is an assay for increased interferon gamma in response to M. tuberculosis antigens. It is used to diagnose latent TB in patients who have previously been vaccinated with BCG. The tuberculin skin test shows a false positive with prior BCG vaccination; interferon gamma release assays do not.

Pleural fluid

Incorrect. Body fluids are not routinely drawn for culture of TB unless there is a clinical suspicion that they are infected.

Bronchoscopy with alveolar lavage and biopsy

Incorrect. Four specimens are acceptable for pulmonary TB: sputum from coughing, induced sputum, gastric aspiration and bronchoscopy. Bronchoscopy is not the first choice since it is invasive.

Summary