Understanding a Positive TB Skin Test: What It Means

Tuberculosis skin tests are typically given to individuals with a known risk factor for developing tuberculosis. A positive reaction on a TB test indicates exposure to tuberculosis bacteria, but does not necessarily indicate the actual presence of tubercular disease.

Testing

• A TB skin test involves the injection of a solution called purified protein derivative beneath the top layer of skin on the inner forearm, according to Lab Tests Online. Typically, a healthcare professional will check this spot for results in a period of two to three days.

Positive Reactions

• Generally speaking, a positive PPD reaction manifests as a raised, red circle at the testing site, notes Lab Tests Online. The size of the reaction area, combined with factors including age and overall health, determines whether results are positive for a given individual.

Follow-Up Testing

• The American Academy of Family Physicians notes that doctors typically follow up a positive result with a physical exam and chest X-rays to spot cases of active, contagious tuberculosis.

Considerations

• Only roughly 10 percent of individuals with a positive PPD test will develop active tuberculosis, notes the AAFP.

Recommendations

• To prevent active TB after a positive test reaction, the AAFP recommends an extended course of the antibiotic isoniazid, combined with health monitoring.