Dear Helmi,

 I believe by asking that question, you are indirectly referring to the sensitivity and specificity of IGRA as a tool to detect tuberculosis. A positive IGRA test might suggest 3 things actually: 1) Latent TB 2) Active TB 3) Recent exposure to TB. The same rules apply to Mantoux tests albeit difficult and often reader/operator dependent.

 The reading of IGRA could also vary depending on test subjects: immunosuppressed individuals may not be able to mount enough immune reaction to give some form of concrete reading. Hence, sensitivity/specificity of IGRA is situational.

 Thus, in summary, the answer to your question would be directly related to the situation in which you conduct your test. Do refer to the following

Diel R, Loddenkemper R, Nienhaus A. Evidence-based comparison of

commercial Interferon - γ Release Assays for detecting active TB. Chest

2010; 137: 952-68.

Lee JY, Choi HJ, Park IN, et al. Comparison of two commercial Interferon -

γ Release Assays for diagnosing Mycobacterium tuberculosis infection. Eur

Respir J 2006; 28: 24–30.

Beglinger C, Dudler J, Mottet C, et al. Screening for tuberculosis infection

before initiation of anti TNF-α therapy. Swiss Med Weekly 2007; 137: 621-

22.

Piana F, Codecasa R, Cavallerio P, et al. Use of a T-cell-based test for

detection of tuberculosis infection among immunocompromised patients.

European Respiratory Journal 2006; 28(1): 31-4.

Piana F, Codecasa LR, Baldan R, et al. Use of T-SPOT.TB in latent

tuberculosis infection diagnosis in general and immunosuppressed

populations. New Microbiologica 2007; 30: 286-90.

Brock I, Ruhwald M, Lundgren B, Westh H, Mathiesen LR, Ravn P. Latent

tuberculosis in HIV positive, diagnosed by M. Tuberculosis Specific

Interferon - γ test. Respiratory Research 2006; 7( 56): 1-6.

Richeldi L. An update on the diagnosis of tuberculosis Infection. Am J

Respir Crit Care Med 2006; 174: 736–42.

Hope this helps.

Rabin

A single negative test will not exclude the diagnosis

Hi Thanks for all the answers.. I know that there are data behind positive IGRA and possibility of active TB.. However the true can't be said in the other direction as the absence of evidence doesn't necessarily mean the evidence of absence esp. when one comes to such test like IGRA.. Its not as simple as the + test means a presence of a disease thus it should work in the other direction...

Thanks a lot Shahban... Really appreciate it

interferon gamma test alone can not rule out tuberculosis. In case of immunodeficient there may not be increased interferon gamma.

We can not rely upon INF gamma alone for diagnosis of tuberculosis

I rather not use this expensive test actually to test active TB... not TST too 

Its just my opinion, IGRA test should be performed as screening test for those asymptomatic individual, but have indications for TB infection.

IGRA also can be used as a TB screening tool for:

i. individuals has history contact to PTB patients, as a screening for LTBI.

ii. Health care workers for TB screening (for those working TB patients/samples)

iii. TB screening for Extrapulmonary TB patient. If IGRA is positive, can follow up for TB workout.

TQ.