Tubercular protein, in the context of tuberculosis diagnosis, refers primarily to tuberculin, specifically Purified Protein Derivative (PPD), which is a mixture of proteins used in the tuberculin skin test.
Here's a breakdown:
- Tuberculin: This is a substance derived from Mycobacterium tuberculosis, the bacteria that causes tuberculosis (TB).
- Purified Protein Derivative (PPD): PPD is a more refined and standardized form of tuberculin. It contains a complex mixture of proteins extracted from the bacteria. These proteins trigger an immune response in individuals who have been previously exposed to TB.
How it works in the Tuberculin Skin Test:
- A small amount of PPD tuberculin is injected under the skin (usually on the forearm).
- If the individual has been infected with TB bacteria in the past, their immune system will recognize the proteins in the PPD.
- This recognition triggers a localized immune response at the injection site, causing an area of swelling and induration (hardening).
- The size of the induration is measured after 48-72 hours, and this measurement is used to determine whether the test is positive or negative. A positive test suggests a previous TB infection.
Important Considerations:
- The tuberculin skin test (TST) doesn't differentiate between latent TB infection (LTBI) and active TB disease. Additional tests are needed to confirm active TB.
- The TST is not perfect and can have false-positive and false-negative results. Factors like previous BCG vaccination or certain medical conditions can affect the results.
- Other TB tests, such as Interferon-Gamma Release Assays (IGRAs), measure the immune system's response to TB proteins in a blood sample. IGRAs are sometimes preferred over the TST, particularly in people who have received the BCG vaccine.
In summary, "tubercular protein" in the context of the question usually refers to the proteins within tuberculin PPD, which are key components used in skin tests to detect TB infection.
