Health and Fitness

What Is The Process Of Reading The Tuberculosis Skin Test?

SWhat Is A Tuberculosis Skin Test? 

A tuberculosis skin test assesses whether or not a person has established a response to the tuberculosis-causing bacteria (TB). This reaction can occur if someone has active tuberculosis, has been exposes to it in the past, or has taken the BCG tuberculosis vaccine (which is not administer in the U.S.). According to estimates, one-third of the world’s population carries latent tuberculosis, and millions of people die from the disease each year. A tuberculosis skin test is often known as PPD (purified protein derivative) test. 

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

After being exposed to the TB germs, the PPD test normally requires a two to the twelve-week incubation period. A tuberculosis skin test is available to anyone, and doctors can safely provide it to newborns, pregnant women, and HIV-positive individuals. People who have 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 a raised, thickened local area of skin reaction. The most important thing to look for is induration, no redness or bruising. When the induration is at its largest, 48-72 hours after the injection, perform skin testing. After 72 hours, tuberculosis tests are likely to underestimate the amount of the induration and are therefore inaccurate.

The presence or absence of induration, as well as the extent of induration, are uses to reads the tuberculosis skin test (localized swelling). The diameter of the induration will be measures in millimeters and measured transversely (for example, perpendicular) to the long axis of the forearm. The reaction to tuberculin is indicates 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 combination with certain patient-specific risk factors, is used to classify a tuberculin reaction as positive. Indulgence more than or equal 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 (vesiculation).

The diameter of the swelling creates by the injection will be measures by your healthcare professional to determine the tuberculosis skin test findings. 

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

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

A 5 mm firm swelling at the location is regard as positive for the following:

  • Those infected with HIV/AIDS 
  • Those who have undergone organ transplantation 
  • Who have an immune system that is weak or who are on steroid therapy 
  • Those who have had intimate contact with someone who has active tuberculosis 
  • 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 regardes 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 calls 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 reads between 48 and 72 hours. Unless there has been a significant reaction to the tuberculosis skin test previously. The test can be redones 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 computed 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 treat for tuberculosis. This will make it easier for healthcare providers to evaluate the results of future tuberculosis skin tests. It is critical to have open communication with your healthcare practitioner. So that they can address any issues or questions you may have.

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