Tuberculosis PPD Skin Test
Tuberculosis, abbreviated as TB, is a chronic or acute bacterial
infection that primarily attacks the lungs. However, it may also affect the
kidneys, bones, lymph nodes, and brain. The disease is caused by Mycobacterium
tuberculosis, a rod-shaped bacterium. Symptoms of TB include coughing, chest
pain, shortness of breath, loss of appetite, weight loss, fever, chills, and
fatigue. Children and people with weakened immune systems are the most
susceptible to TB. Half of all untreated TB cases are fatal.
The tuberculosis skin test, also known as the tuberculin test or PPD test, is a test used to determine if someone has developed an immune response to the bacterium that causes tuberculosis. This response may occur if someone currently has TB, was exposed to it in the past, or if they received the BCG vaccine against the disease.
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The tuberculosis bacterium produces a delayed-type hypersensitivity skin reaction to certain components of the bacterium which is used to test tuberculosis through the skin. The components of the organism are contained in extracts of culture filtrates and are the core elements of PPD or the purified protein derivative, which is regarded to be a classic tuberculin.
Reaction of the skin to the tuberculin PPD begins when specialized immune cells called T cells, which have been sensitized by prior infection, are recruited by the immune system to the site of the skin where they release lymphokines or the chemical messengers. These lymphokines induce induration, which is a hard, raised area with clearly defined margins in and around the injection site through local vasodilation or the expansion of the diameter of blood vessels. This condition may lead to fluid deposition, which in turn, is highly related to edema, fibrin deposition, and recruitment of other types of inflammatory cells to the area.
An incubation period of two to 12 weeks is usually necessary after exposure to the TB bacteria in order for the PPD test to be positive. The tuberculosis PPD skin test is recommended for individuals who are suffering from the disease in order to determine its extent and provide the necessary cure. Doctors are duly qualified to perform these tests and guide their patients toward recovery.