When the patient returns between 48 and 72 hours for TST reading, after proper hand hygiene, gently sweep the fingers over the forearm feeling for induration. If an area is felt, carefully mark the horizontal edges only and measure with calipers. Be sure to disregard erythema. Redness is not an indication of a positive test. Measure only the indurated area, and only from side-to-side.
Is It Positive?
It is important to know that there is not one particular measurement that means positive for everyone. For this reason, results should be documented by measurement in millimeters, not positive or negative.
Congratulations!
You are now equipped to go out there and identify TB infection. Remember, in most cases TB infection is latent, so the patient will have no symptoms and is unable to infect others. It is only when M. tuberculosis is actively growing, known as TB disease, that the patient exhibits symptoms and may be infectious to others.