Tuberculin

Tuberculin

A Mantoux tuberculin skin test being administered.

Tuberculin is a protein derivative used in the diagnosis of tuberculosis (TB). It is primarily used in the Mantoux test, which is a method for detecting Mycobacterium tuberculosis infection.

History

Tuberculin was first developed by Robert Koch in 1890. Initially, it was intended as a treatment for tuberculosis, but it was later found to be ineffective for this purpose. However, it proved useful as a diagnostic tool. The original preparation, known as "old tuberculin," was later refined into "purified protein derivative" (PPD), which is used today.

Composition

Tuberculin is composed of proteins derived from the Mycobacterium tuberculosis bacterium. The most commonly used form is the purified protein derivative (PPD), which is a standardized preparation that ensures consistent results in diagnostic testing.

Uses

The primary use of tuberculin is in the Mantoux test, which is a skin test used to determine if a person has been exposed to the tuberculosis bacterium. A small amount of PPD is injected intradermally, and the site is examined after 48 to 72 hours for signs of an immune response, such as induration and redness.

Administration

The Mantoux test is administered by injecting 0.1 mL of PPD into the inner surface of the forearm. The injection should create a small, pale elevation of the skin (a wheal). The test site is then evaluated after 48 to 72 hours for the presence of induration, which is measured in millimeters.

Interpretation

The results of the Mantoux test are interpreted based on the size of the induration and the individual's risk factors for tuberculosis. A larger induration is more likely to indicate a positive result, suggesting TB infection. However, false positives can occur, especially in individuals who have received the BCG vaccine or have been exposed to non-tuberculous mycobacteria.

Limitations

The Mantoux test has several limitations. It cannot distinguish between latent and active TB infection, and it may produce false positive or false negative results. Factors such as HIV infection, malnutrition, and immunosuppression can affect the test's accuracy.

Related pages

• Tuberculosis
• Mantoux test
• Robert Koch
• BCG vaccine

References

• Koch, R. (1890). "The etiology of tuberculosis". Berliner Klinische Wochenschrift.
• Centers for Disease Control and Prevention. "Tuberculin Skin Testing". Retrieved from [CDC website].