Tuberculin, also known as purified protein derivative, is a combination of proteins that are used in the diagnosis of tuberculosis. This use is referred to as the tuberculin skin test and is recommended only for those at high risk. Injection is done into the skin. After 48 to 72 hours if there is more than a five to ten millimeter area of swelling the test is considered positive

Common side effects include redness, itchiness, and pain at the site of injection. Allergic reactions may occasionally occur. The test may be falsely positive in those who have been previously vaccinated with BCG or have been infected by other types of mycobacteria. The test may be falsely negative within 10 weeks of infection, in those less than 6 months old, and in those who have been infected for many years. Use is safe in pregnancy. Tuberculin is made out of an extract of Mycobacterium tuberculosis.

Tuberculin was discovered in 1890 by Robert Koch. He initially believed it was a cure for tuberculosis, which turned out not to be the case. It is on the World Health Organization's List of Essential Medicines, the safest and most effective medicines needed in a health system. The wholesale cost in the developing world is about 0.22 USD per dose. In the United States testing costs less than 25 USD.

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