What Should I Expect after a Positive TB Test?
The tuberculin test, also known as the PPD test, refers to an intradermal test that uses intradermal injection of tuberculin and diagnoses type IV hypersensitivity caused by tuberculosis infection based on the skin condition of the injection site. Tuberculin is a bacterial component of Mycobacterium tuberculosis, including pure protein derivatives (PPD) and old tuberculin (OT). This test has reference significance for diagnosing tuberculosis and measuring non-specific cellular immune function of the body
Basic Information
- Chinese name
- Tuberculin test
- nickname
- PPD test
- experiment method
- Intradermal injection
- Clinical significance
- Provide evidence for BCG vaccination
Tuberculin test test method
- Intradermal injection is commonly used, and the dosage of PPD: the first test solution contains 0.0001 mg per 0.1 mL. OT generally uses a 1: 100,000 dilution for the first time to prevent serious skin and systemic reactions. After routine disinfection, the test solution is injected into the flexion of the forearm, and the results are observed for 48 to 72 hours. If the results are not clear at 48 hours, the results of 72 hours shall prevail. Pay attention to the local induration. Do not use the redness alone as the standard. .
Interpretation of tuberculin test results
- The test site has no redness and induration as (-); the test site has needle-like red spots or a little redness and swelling, and the induration diameter is less than 0.5cm (±); the test site has red and induration diameters of 0.5 to 0.9cm (+) The diameter of the redness and induration of the test site is 1.0 to 1.9cm (++); the diameter of the redness and induration of the test site 2cm is (+++); except for the redness and induration, local blisters and necrosis are (++ ++).
Clinical significance of tuberculin test
- 1. The tuberculin test for diagnosis and differential diagnosis has an important role in the diagnosis and differentiation of tuberculosis in adolescents, children and the elderly, and is an important auxiliary examination method.
2. Provide evidence for BCG vaccination. For example, if the tuberculin test is positive, it indicates that the body has been infected with tuberculosis bacteria. Those who were negative for the tuberculin test were vaccinated against BCG.
3. To provide a basis for determining the immune effect Generally, a tuberculin test is performed 3 months after the BCG vaccine is inoculated to understand whether the body has immunity to the BCG vaccine. If the tuberculin test is positive, it indicates that the BCG vaccine was successfully inoculated. Otherwise, the BCG vaccine should be re-inoculated.