Positive tuberculosis skin test results do not necessarily indicate a person has active tuberculosis or is contagious. Usually, after a person comes back with a positive purified protein derivative (PPD) skin test, additional testing is needed to determine if active tuberculosis is present. Additional tests will include a chest X-ray and a review of his or her symptoms. Depending on those results, further tests and treatment may be needed.
To understand what happens after positive tuberculosis (TB) skin test result, its important to know what a TB test is. During a PPD test, also known as a mantoux test, a small amount of tuberculosis antigens — called tuberculin — is injected under the skin. The spot of the injection is examined between 48 and 72 hours after the injection to check for a raised area of the skin, known as an induration. If a TB skin test is positive, it means the person has a response to the bacteria that causes tuberculosis. This does not necessary mean the person has symptoms or active disease.
If positive tuberculosis skin test results occur, the first test ordered is usually a chest X-ray. An X-ray can determine if infiltrates or lesions are present in the lungs, which may indicate active TB. A symptom checklist will also usually be reviewed to determine if signs of TB, such as weight loss, coughing up blood, fever, and night sweats are present. If the chest X-ray is normal and no symptoms are present, no further testing is usually needed.
In some cases, people without active TB, but who have positive test results, may be put on medication. The bacteria that causes TB can show up in someone with a positive skin test, but may be dormant. Medication may be given as a precaution to prevent the bacteria from becoming active in the future.
When a chest X-ray indicates signs of TB or symptoms are present, a person may have active tuberculosis. At this point, sputum samples will need to be analyzed to confirm the presence of the bacteria. The person will also need to be kept away from close contact with other people to prevent spreading the disease. If active TB is present, antibiotic medication will be given to treat it.
Once a person has a positive tuberculosis skin test, he will likely have positive tests in the future. PPD skin tests are a routine requirement for some types of employment and school admission. For people with a history of a positive PPD skin test, a yearly symptom checklist is usually performed instead.