This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Lab Investigations, Subject name: Microbiology
Test done for mycobacterium tuberculosis by whole blood is : 
Select and explain. 
A. BACTEC, B. IGRA, C. GeneXpe, D. Culture
B: IGRA
Answer: B: IGRA 
Explanation: IGRA is interferon gamma release assay .In this test,we target up with the aificial intake of mycobacterium like ESAT-6,CFP-10,TB-7.7, by adding the sample blood(sensitized ) having T-cells which release interferon gamma and its activity can be measured. It is highly specific and there are no positive results.