Tuberculosis: Sensitivity and Specificity

Introduction: Tuberculosis is a major health hazard due to its high contagiousness and ability to exist in a latent state in the host.

Note that the tests have all been assessed for patients with active TB (since there is no gold standard for latent TB).

There are two major tests being used currently to detect latent TB infection - the PPD skin test and the T cell activation blood test.

Note that these are also used in the evaluation of active TB, though they are supplanted (for pulmonary TB) by chest x-ray and sputum AFB stain/culture.

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Tags: Infection tuberculosis Tag this Diagnosis.

The sensitivity and specificity of findings for Tuberculosis are listed below. See the left navigation bar to change the display.

Pre-Test Probability (Prevalence): %.	Post-Test Probability (Predictive Value): %.	Switch to display mode.
Note that calculating probabilities from more than one** finding is inherently inaccurate because findings are not independent. (For example, using two positive findings that share a common pathogenesis is likely to overestimate the true probability.)

Sensitive and Specific Findings
Finding	Result	Sensitivity	Specificity
[ + ] T-Spot	+ 0 -	94%	100%
active TB, HIV-negative adults specificity is vs bCG-vaccinated population Study: Am J Respir Crit Care Med. 2006 Oct 1;174(7):736-42. PMID: 16799073
[ + ] T-Spot	+ 0 -	90%	100%
active TB, HIV-positive adults specificity is vs bCG-vaccinated adults Study: Am J Respir Crit Care Med. 2006 Oct 1;174(7):736-42. PMID: 16799073

Specific Findings
Finding	Result	Sensitivity	Specificity
[ + ] Sputum AFB Smears	+ 0 -	67.5%	97.5%
active TB. Three successive smears Study: J Clin Microbiol. 2002 Sep;40(9):3482-4. PMID: 12202598
[ + ] Quantiferon	+ 0 -	81%	97%
active TB, HIV-negative adults specificity is vs bCG-vaccinated adults Study: Am J Respir Crit Care Med. 2006 Oct 1;174(7):736-42. PMID: 16799073

Sensitive Findings
Finding	Result	Sensitivity	Specificity
[ + ] Purified Protein Derivative (PPD)	+ 0 -	90%	35.4%
adults with active TB >=10mm threshold for induration specificity in Japanese adults with a high rate of bCG vaccination. Note that non-TB mycobacterium (e.g. avium) also causes false positives: in US health care workers, in one study 50% of indurations 10-14mm were from M avium (PMID 11769770). Some centers use a 'booster' or serial PPD strategy whereby a second PPD is placed 1-4 weeks after the first. The idea is to generate a stronger immune reaction in the second test, given that the reaction may be blunted if the initial TB exposure was long ago. This has not been evaluated for specificity. Study: sensitivity from UpToDate http://www.utdol.com/online/content/topic.do?topicKey=tubercul/13154 specificity from Am J Respir Crit Care Med. 2004 Jul 1;170(1):59-64. PMID: 15059788