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Case 5: A 32-Year-Old with Chronic Cough

You answered:

B If the pleural effusion is tapped, there is greater than 80% likelihood that a Ziehl-Neelsen stain of pleural fluid will show AFB.

This answer is incorrect. Pleural fluid sent for AFB staining has a sensitivity of only 10-25%, and the sensitivity of pleural fluid culture ranges from 25-66%. Histologic examination of pleural biopsy specimens, when combined with mycobacterial culture of pleural fluid or pleural biopsy material, can yield the diagnosis in 90-95% of cases.

Choose another answer:

A If a nucleic acid amplification test on sputum is positive for Mycobacterium tuberculosis, sputum culture is not required.
C The patient’s small tuberculin skin test reaction is probably due to prior BCG vaccination, and an alternative diagnosis should be sought.
D Therapy for TB should be initiated while the diagnostic work-up continues.
E The patient’s CD4 cell count is almost certainly less than 100 cells/mm3.

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