What is tuberculin?

Tuberculin is a purified protein derivative (PPD) of the bacterium that causes tuberculosis (TB), *Mycobacterium tuberculosis*. It is used in the Mantoux test, also known as the tuberculin skin test, to diagnose TB infection.

The Mantoux test involves injecting a small amount of tuberculin into the skin. If a person has been infected with TB, their immune system will react to the tuberculin, causing a raised, hardened area (induration) to develop at the injection site. The size of the induration is measured and interpreted by a healthcare professional to determine if a person has been infected with TB.

A positive tuberculin skin test does not necessarily mean that a person has active TB disease. It indicates that the person has been infected with TB at some point in their life, but it is possible that the infection is inactive and not causing any symptoms. Further tests, such as a chest X-ray and sputum culture, may be needed to confirm an active TB infection.

Tuberculin is also used in the tuberculin tine test, which is a less common method of TB testing. The tuberculin tine test involves applying a small amount of tuberculin to the skin and then pricking the skin with a needle. If a person has been infected with TB, a small bump (papule) will develop at the injection site within 48 to 72 hours.