This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
True about tuberculin test are all except ? 
Select and explain. 
A. Recent conversion in adult is an indication for ATT, B. INH prophylaxis is staed if the test is positive, C. No risk in negative, D. May be false negative in immunocompromised patients
C: No risk in negative
Answer: C: No risk in negative 
Explanation: Ans. is `c' i.e., No risk in negative . Persons who have never had contact with tubercle bacilli are tuberculin negative. It means they are susceptible to T.B. infection as they have not developed cell mediated immunity against M. tuberculosis. About other options Option 'a' Indication for chemoprophylaxis by ATT. 1) Contacts of open cases who show recent montoux conversion (option 'a') 2) Children with positive montoux and a TB patient in the family. 3) Neonate of tubercular mother. 4) Patients of leukemia, diabetes, silicosis, or those who are HIV positive but are not energic, or are on coicosteroid therapy who show a positive Mantoux. 5) Patients with old inactive disease who are assessed to have received inadequate therapy. Option 'b' Is paially correct, because positive tuberculin test is not an indication for prophylaxis in all cases, but it is an indication for chemoprophylaxis for the contacts of open cases. Option 'd' Test may be false negative in immunocompromized patients - Ananthanarayan p. 361.