A negative reading on a tuberculin skin test means a person had no reaction to the tuberculin antigen injected near the surface of his skin. Therefore, he is not positive for tuberculosis, explains WebMD.
Redness alone at the site of the injection is not an immediate diagnosis of tuberculosis. Without a firm bump rising, redness can be a result of mild irritation from insertion of the needle. If a patient experiences severe itching at the site of the injection, WebMD recommends using a cold cloth to soothe the skin and avoid itching, as this could tamper with the results.
A positive TB test results in a firm red bump at the site of the injection but can only be accurately diagnosed with a doctor's interpretation, notes WebMD. Doctor cannot tell from the test if the positive result means the infection is active and contagious or inactive and latent.
If a patient receives a positive result for tuberculosis, further testing is required; this includes a chest X-ray and a sputum culture to accurately determine infection diagnosis, according to WebMD. Strong positive reactions to the TB skin test could result in a fever, swollen lymph nodes in the armpit or swelling in the patient's arm.