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What does a negative reading on a TB skin test mean?

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Quick Answer

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.

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Full Answer

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.

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