The skin test should be read between 48 and 72 hours after administration. A patient who does not return within 72 hours will probably need to be rescheduled for another skin test.

How Mantoux test is read?

The reaction is read by measuring the diameter of induration (palpable raised, hardened area) across the forearm (perpendicular to the long axis) in millimeters. If there is no induration, the result should be recorded as "0 mm". Erythema (redness) should not be measured.

When Mantoux test is negative?

A Tb Mantoux test results may sometimes be negative, but that does not always mean that a person is free of tuberculosis. This is mainly because sometimes if a person is exposed to the bacteria, there is an incubation period of two to twelve weeks for the PPD test to be positive.