The tuberculin test requires observation for 48-72 hours after tuberculin inoculation, and the results are interpreted according to the erythema at the inoculation site. The tuberculin test is a primary screening test for active tuberculosis infection and is performed by intra-dermal injection of tuberculin for 72 hours, with a negative result if the erythema is <5 mm, indicating no tuberculosis infection. If the erythema is 5-10 mm, a weakly positive result is indicated, and if the erythema is 10-20 mm, a positive result is indicated. Either a weakly positive or a positive result indicates a previous infection with tuberculosis and not necessarily active tuberculosis at present. If the result is strongly positive, that is, if the erythema is >2 cm, or if blistering, rupture, or necrosis is present, the possibility of active tuberculosis infection is considered.