Investigations

• interferon gamma (positive if >140 pg/ml) ^c
• adenosine deaminase (positive if > 45 U/l) ^b  

Why?

• A tuberculin test alone cannot safely diagnose or exclude TB ^c

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
pleural effusion b (pre-test probability: 23%)	tuberculous effusion (biopsy, histology or culture)	adenosine deaminase (> 45 U/l)	4.5 (2.4 to 8.7)	86%	0.27 (0.17 to 0.44)	26%
pleural effusion c   (pre-test probability: 23%)	tuberculous pleurisy (biopsy)	interferon gamma (> 140 pg/ml)	12 (6.1 to 21)	79%	0.062 (0.016 to 0.24)	2%
pleural effusion c (pre-test probability: 39%)	malignancy or granulomatous disease (culture or biopsy)	positive tuberculin test	2.0 (1.0 to 3.8)	56%	0.74 (0.54 to 1.00)	32%