What Is the Tuberculosis Skin Test Reading Procedure?

What Is A Tuberculosis Skin Test? 

A tuberculosis skin test considers whether or not a person showed a response to the tuberculosis-causing bacteria (TB). This response can occur if somebody has active tuberculosis, has been revealed to it in the past, or has taken the BCG tuberculosis vaccine (which is not administered in the U.S.). According to estimations, one-third of the world’s population carries latent tuberculosis, and millions of people die from the illness each year. A tuberculosis skin test is usually known as PPD (purified protein derivative) test. 

tuberculosis skin test

Tuberculosis test works on the idea that M. tuberculosis bacteria induces hypersensitivity skin reaction to certain bacterium components. The components of the organism are drawn from TB cultures by medical practitioners and constitute the basis of the conventional tuberculin PPD (also known as purified protein derivative). A tuberculosis test is accomplished with this PPD material. The immune system attracts specialized immune cells known as T cells, which have been sensitized by earlier diseases, to the skin area, where they have chemical messengers known as lymphokines.

After being revealed to the TB germs, the PPD test normally needs a two to the twelve-week incubation period. A tuberculosis skin test is open to anyone, and doctors can safely provide it to newborns, pregnant women, and HIV-positive individuals. People who hold had a strong reaction to a previous tuberculosis skin test are the only ones who should avoid it.

Process Of Reading A Tuberculosis Test

When you read a tuberculosis skin test, you’re looking for induration, which is an extended, thickened local area of skin reaction. The most important thing to examine for is induration, no redness or bruising. When the induration is at its enormous, 48-72 hours after the injection, perform skin testing. After 72 hours, tuberculosis tests are possible to underestimate the amount of the induration and are therefore inaccurate.

The presence or lack of induration, as well as the extent of induration, are used to read the tuberculosis skin test (localized swelling). The diameter of the induration will be calculated in millimeters and measured transversely (for example, perpendicular) to the long axis of the forearm. The reaction to tuberculin is characterized by induration (a perceptible, elevated, hardened region around the injection site). It’s worth noting that redness isn’t a metric. 

The diameter of the induration, in mixture with certain patient-specific risk factors, is used to classify a tuberculin reaction as positive. Indulgence of more than or equivalent to 15 mm is considered a positive skin test in a healthy person with a normal immune system. The tuberculosis test is negative if there are blisters.

The diameter of the swelling produced by the injection will be measured by your healthcare professional to decide the tuberculosis skin test findings. 

If the tuberculosis test was negative, the skin where it was insinuated would not enlarge or will swell just slightly. If the tuberculosis skin test is positive, the patient will experience swelling, but the size will change. 

15 mm or more of the firm bump at the location suggests a positive response in persons who have no known TB concerns. 

A 5 mm firm streaming at the location is regarded as positive for the following:

  • Those infected with HIV/AIDS 
  • Those who have experienced organ transplantation 
  • Those who have an immune system that is weakened or who are on steroid therapy 
  • Those who have had intimate contact with someone who has active tuberculosis 
  • Those who exhibit alterations on a chest X-ray that appear to be related to previous tuberculosis 

A tuberculosis skin test that is more than or equal to 10 mm is regarded positive for the following: 

  • Diabetes, renal failure, and other factors that raise the risk of active tuberculosis 
  • Those who work in the mycobacteriology lab are called mycobacteriologists. 
  • Users of injectable drugs 
  • Immigrants have arrived in the last five years from a nation with a high TB rate.


You will need to take another tuberculosis test if your results are not read between 48 and 72 hours after the test. Unless there has been a significant reaction to the tuberculosis skin test previously, the test can be redone as soon as possible. 

If your tuberculosis test is positive, your doctor will order more tests to determine whether or not you have active disease. Chest X-rays and culture of a sputum sample, a viscous fluid produced in the lungs as a result of disease, are among these tests. Magnetic resonance imaging (MRI) and calculated tomography (CT) scans are two other options.


If you’ve ever tested positive for tuberculosis, you’ll always have a positive tuberculosis skin test result, even if you’ve been treated for it. Your healthcare practitioner will make a note in their medical records that you were treated for tuberculosis. It is necessary to have open communication with your healthcare practitioner so that they can address any issues or questions you may have.

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Naman Modi is a Professional Blogger, SEO Expert & Guest blogger at?www.wilmingtonurgentclinic.com.He is an Award-Winning Freelancer & Web Entrepreneur helping new entrepreneurs launch their first successful online business.