Q: 44 year old male, recently migrated from a developing country is admitted to ICU with 'sepsis kind of picture', hypotension, fever, cough and low grade fever. CXR showed cavitary lesion at right upper lobe. Interferon-gamma release assays (IGRAs) is ordered by an on-call resident, which is reported negative now. Negative IGRAs rule out the active tuberculosis (TB). 

A) True
B) False


Answer: False

IGRAs is still a controversial test and has raised many eyebrows of experts as it has 'issues' with reproducibility in  labs, and require many perfect technical parameters. IGRAs can be a good diagnostic tools for latent tuberculosis infection (LTBI). But, it cannot distinguish between latent infection and active tuberculosis (TB).

A positive IGRA result may not necessarily indicate active TB, and a negative IGRA result may not rule out active TB.


References:

1. Menzies D, Pai M, Comstock G. Meta-analysis: new tests for the diagnosis of latent tuberculosis infection: areas of uncertainty and recommendations for research. Ann Intern Med 2007; 146:340.

2. Metcalfe JZ, Everett CK, Steingart KR, et al. Interferon-γ release assays for active pulmonary tuberculosis diagnosis in adults in low- and middle-income countries: systematic review and meta-analysis. J Infect Dis 2011; 204 Suppl 4:S1120.

3. Mazurek GH, Jereb J, Vernon A, et al. Updated guidelines for using Interferon Gamma Release Assays to detect Mycobacterium tuberculosis infection - United States, 2010. 

4. MMWR Recomm Rep 2010; 59:1. 2. Sester M, Sotgiu G, Lange C, et al. Interferon-γ release assays for the diagnosis of active tuberculosis: a systematic review and meta-analysis. Eur Respir J 2011; 37:100.