A positive tuberculin test is indicated by an area of induration of
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
<5mm in diameter
6-9mm in diameter
>10mm in diameter
No induration
Bacteriology