The Tuberculin Skin Test Or Purified Protein Derivative (PPD) 

The PPD is not a vaccine, but a screening test to detect exposure to tuberculosis. Tuberculosis is a disease caused by the bacteria Mycobacterium tuberculosis. Formerly known as "consumption" -- for all you opera fans -- this bacterial infection commonly affects the lungs but can also spread to other parts of the body (extrapulmonary TB). TB in the lungs is easily spread to other people through simple coughing. In Puccini's opera, La Boheme, Mimi contracts tuberculosis and dies at the end. Today, there is treatment for this disease, but it involves a multidrug protocol that can average from six to nine months.

The PPD is a useful screening tool to detect exposure to TB because everyone exposed to tuberculosis does not necessarily develop the disease. Any health-care provider can administer a PPD, which involves injecting a small amount of inactive TB into your skin. After 48 hours, the area injected is checked to detect a skin reaction. If the area is red or raised, then this is a positive PPD. Only a health- care provider can determine this because the area of swelling must be measured. All positive PPDs should be followed up with a chest X-ray. If the X-ray shows no evidence of lung tuberculosis, then your healthcare provider should discuss taking the antibiotic called isoniazide as a prophylaxis against developing tuberculosis in the future. Annual PPDs are recommended for all patients, especially those who are HIV positive, but if you know you are PPD positive, then make sure to tell your health care provider. This test should not be repeated, for fear of a stronger reaction to the PPD.