Positive TB Skin Test? What next?
April 7, 2014
Positive TB Skin test or negative? It will be a burden for a person who take TB skin test in laboratory. Should we worry about that? Statistics said that one third population in the world are being infected by tuberculosis. Is that including us?
The easiest way to know whether you are infected TB is Tuberculin Skin Test (TST) to know if you are positive TB skin test or not. TST in laboratory is also known as Mantoux test. Not all the result will be confess as reliable. Because the reliable reading of Mantoux TST requires standardization of procedures, supervision, practice, and training.
How to get Positive TB skin test?
TST is conducted by injecting tuberculin PPD (purified protein derivative) into the intradermal of the forearm. About 0.1 ml tuberculin will be injected into the inner surface of the forearm to produce an elevation of the skin with 6 to 10 mm in diameter.
How to read Positive TB skin test?
We can read the reaction between 48 and 72 hours after injection. If the patient does not return within 72 hours, he will need to be retested by another skin test. The reaction is measured in the size of diameter of induration (in mm). Don’t measure the redness. Measure at the perpendicular to the long axis across the forearm.
If the diameter of the induration is 15 or more millimeters, it is considered to be positive in any person. We don’t have to look at the high risk factor for TB. It must be positive TB skin test.
If the diameter is 10 or more millimeters , it is considered to be positive in some condition, such as :
- Recent immigrants (<5 years) from high prevalence countries
- Mycobacteriology laboratory personnel
- The user of drug injection
- Children <4 years of age
- Infants, children or adolescents that exposed to adults with high risk condition
- Residents of high risk congregate settings
If the diameter is 5 or more, it is considered to be positive in some condition, such as :
- Patients with organ transplants
- HIV infected persons
- Patien with fibrotic changes on chest radiograph that are consistent with prior TB
- The patient has recent contact with a person with TB
So, what we should do, after getting the result of Positive tb skin test? You should make sure whether you are latent tuberculosis or active tb. If you are latent, you don’t need to do anything. But if you are active TB, you should treat it by Anti tuberculosis treatment.
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