Tuberculosis (TB) is contagious bacterial lung disease that is spread from person to person from droplets released into the air. A person with TB may not aware that he has TB because he does not develop symptoms of the disease. The Mayo Clinic states that TB kills two million people each year. Most cases of TB can be cured with medications that are taken for several months. A tuberculin skin test, also called a PPD test or Mantoux skin test, can be administered to determine whether or not a person has tuberculosis.
Administration
The tuberculin skin test (TST) is given by injecting 0.1 milliliters of tuberculin purified protein derivative (PPD) on the inside of the forearm with a tuberculin syringe. The tuberculin test is called a transdermal injection, which means the PPD is given between the layers of skin called the dermis. As the PPD is injected into the dermis, an elevation of skin, called a wheal, about 10 millimeters in diameter occurs.
Side Effects
Serious side effects from a tuberculin skin test are rare. Some individuals may be sensitive to PPD and experience fever, swollen glands in arms or underarms, skin rashes and ulcers at the site of testing. Slight pain from the injection and itching can occur at the test site, but a cold pack applied can reduce discomfort, the University of New Hampshire Health Services states.
Reading and Interpretation
TSTs are read 48 to 72 hours after they have been placed. If a test is not read within this time frame, it needs to be redone. Positive reactions are raised, hardened or swollen areas where the injection was given. When measuring a PPD test, a person should measure across the forearm. Readings that measure greater than five millimeters are considered positive in people with HIV, a person who has had recent contact with someone who has TB, people who have had organ transplants and patients who are immunosupressed.
A reading of 10 millimeters or more is considered positive in recent immigrants, IV drug users, residents and employees in high-risk settings, mycobaceriology laboratory personnel, children under four years of age and infants, children and teens who have been exposed to adults in a high-risk setting. A reading of 15 millimeters is considered positive in anyone, including people who have no risk-factors for developing tuberculosis.
Positive Results
A person with a positive TST will be required to get a chest x-ray and a physical examination to determine whether or not he has active tuberculosis. A person with active TB is contagious and can spread tuberculosis to other people.
False-Positive Results
A person may test positive even when he has not been infected with tuberculosis. The Centers for Disease Control and Prevention states that reasons for false-positive reactions include incorrect administration of the tuberculin skin test, incorrect reading and interpretation of the reaction or the incorrect bottle of antigen was used. A person who has an infection with a mycobacteria other than tuberculosis can also have a false-positive tuberculin skin test.
