A positive tuberculin test is indicated by an area of induration of: (A) <5mm in diameter, (B) 6-9mm in diameter, (C) >10mm in diameter, (D) No induration
Answer is C. In this test 0.1 ml of PPD containing 5 TU is injected intradermally on the flexor aspect of the forearm with a tuberculin syringe, raising a wheal. The site is examined48-72 hrs later and the induration of: > 10mm: positive 6-9mm : equivocal /doubtful <5mm : negative Ref: Textbook of microbiology; Ananthanarayan and paniker's; 10th edition; Pg: 360