Delayed hypersensitivity in skin tests, is assessed by

Intradermal test for delayed hypersensitivity - Usually employed for infectious diseases. - Antigen is prepared from the respective infective agents and injected intradermally. - Significantly indurated nodule after 48 hrs is considered to indicate delayed hypersensitivity to the antigen. - Test continues to remain positive even after the infection has subsided, though active infections usually produce more severe reactions. -In overwhelming infections the test can completely become negative because of the suppression of delayed hypersensitivity. Erythema- redness of the skin or mucous membranes due to increased flow in superfiial cappillaries Bulla- clear fluid filled lession with size mor tha 0.5 cm Necrosis-irreversibe cell injury leading to cell death due to denaturation of proteins / enzymatic digestion of cells. it is always pathological and associated with inflamation