tuberkülin

Tuberkulin is a sterile preparation of proteins derived from *Mycobacterium tuberculosis*, the bacterium that causes tuberculosis. It is primarily used in diagnostic tests for tuberculosis infection. The most common form is purified protein derivative (PPD), which is a mixture of specific proteins from the tubercle bacillus.

When introduced into the body, typically via intradermal injection, tuberculin can trigger an immune response in individuals who have been previously exposed to *Mycobacterium tuberculosis*. This response is a type of delayed-type hypersensitivity. The reaction is characterized by redness and swelling at the injection site, which is measured after a specific incubation period, usually 48 to 72 hours. A positive reaction indicates that the person's immune system has encountered tuberculosis bacteria, either from an active infection, a past infection, or from receiving the BCG vaccine.

It is important to note that a positive tuberculin skin test does not differentiate between latent tuberculosis infection and active tuberculosis disease. Further investigations, such as chest X-rays and sputum tests, are required to confirm an active infection. Conversely, a negative test may indicate the absence of infection, but can also occur in individuals with certain immune deficiencies or recent infections where the immune system has not yet developed a detectable response. Tuberculin testing is a valuable tool in public health for screening and identifying individuals who may require further evaluation for tuberculosis.