Tuberculosis is a prevalent disease mainly affecting the lungs and respiratory organs. An infection of the Mycobacterium tuberculosis bacteria causes it. Exposure to this bacterium can result in either active TB disease or a latent infection, where latent TB indicates that you have an infection without visible signs or symptoms. Furthermore, latent infection can eventually reactivate as a secondary TB infection. In such cases, the patient may experience symptoms including:

Generally, healthcare providers may treat latent TB to avert the chance of developing an active infection in the future. According to the Centres for Disease Control and Prevention (CDC) reports, 1 in 10 people with a latent TB infection will eventually develop an active reinfection, which may develop years after the initial infection.
tb test

A blood or skin work can help healthcare providers diagnose this condition. If your skin test is positive or if you may have a false negative, your doctor may suggest a TB blood test - Tuberculosis Skin Test (Mantoux) or the purified protein derivative (PPD) test. 

Also Read: Tuberculosis: Diagnosis, Causes, Symptoms And Treatment

Dive into this article to learn what this test entails, its purpose, who needs it, preparation, procedure, and how to interpret the results.

Purpose

The primary purpose of the Tuberculosis Skin Test is to determine whether a person has been infected with the bacteria that cause TB. This test helps identify individuals who might have been exposed to TB, even if they do not show any symptoms. Early detection is very crucial to preventing the spread of TB and initiating prompt treatment.

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Who Needs It

The Tuberculosis Skin Test is typically recommended for individuals at higher risk of TB infection or working in environments where TB exposure is possible. This includes healthcare workers, individuals living or working in crowded settings such as prisons or shelters, those who have travelled to or lived in areas with high TB prevalence, and individuals with weakened immune systems.

Preparation

Preparation for a Tuberculosis Skin Test is minimal. It's essential to inform the healthcare provider if you have any medical conditions or are taking any medications, as certain medications or conditions may affect the test results. In addition, pregnant women should seek advice from their healthcare provider before undergoing the test.

What Happens During The Test?

A TB skin test also known as a Mantoux tuberculin skin test (TST), is well tolerated by most people and hardly causes adverse reactions.

The test has two-steps: 

Step one

The healthcare provider injects a small amount of tuberculin beneath the skin, usually in the forearm. Tuberculin is a sterile liquid of a purified protein derivative (PPD) obtained from the bacteria that cause TB.

A tiny, pale bump will develop at the site of injection.

Step two

The healthcare provider will monitor the skin 48 to 72 hours after the injection to check how the skin has responded to the tuberculin extract. The patient’s skin reaction will help the doctor evaluate if they have a TB infection.

If you wait more than 72 hours for a doctor to evaluate the skin, you must start a new test.

During this waiting period, avoiding scratching or rubbing the injection site is crucial.

Also Read: Tuberculosis Diet: Here’s What You Should Eat And Avoid When Recuperating From TB

Results

Interpreting the results of a Tuberculosis Skin Test requires careful observation of the injection site. A positive reaction typically manifests as a raised, red bump at the injection site. The size of the bump and the presence of induration (hardening) are measured to determine the significance of the reaction. It's important to note that a positive response does not necessarily mean active TB disease but indicates exposure to the bacteria. Further screening like chest X-rays or sputum tests, may be necessary to confirm an active infection.

Conversely, a negative reaction indicates that the person has not been infected with TB or has been infected but does not have a strong immune response to the PPD solution. However, false-negative results can occur, particularly in individuals with weakened immune systems.





References:

Mantoux test and its interpretation, Surajit Nayak and Basanti Acharjya

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3481914/

The Tuberculin Skin Test Get access Arrow, Robin E. Huebner, Maybelle F. Schein, John B. Bass, Jr.

https://academic.oup.com/cid/article-abstract/17/6/968/352769?redirectedFrom=fulltext

Disclaimer:

The content provided here is for informational purposes only. This blog is not intended to substitute for medical advice, diagnosis, or treatment. Always seek the advice of a qualified healthcare provider for any questions or concerns you may have regarding a medical condition. Reliance does not endorse or recommend any specific tests, physicians, procedures, opinions, or other information mentioned on the blog.