How is presentation of positive TB test?

➢ If a tissue sample from the site of the positive reaction is examined, it will show infiltration by lymphocytes and monocytes, increased fluid between the fibrous structures of the skin, and some cell death. ➢ If the reaction is more severe and prolonged, some of the activated macrophages will have fused together to form large cells containing several nuclei. An accumulation of activated macrophages of this sort is termed a granuloma ➢ The DTH response in the skin is determined by the extent of induration. ➢ Erythema indicates an immediate HS reaction and begins earlier than induration but often persists even after induration has developed ➢ DTH skin test to most antigens is read as positive when induration is 5mm or more at 48 hours and 72 hours following inoculation.For tuberculin, 10 mm is considered a positive