Why does BCG vaccine cause false-positive TB test?

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Why does BCG vaccine cause false-positive TB test?

Background: Bacille Calmette-Guérin (BCG) vaccination is known to cause false-positive tuberculin skin test (TST) results from cross-reactions with mycobacterial antigens. However, the duration of BCG vaccination influence on the TST is poorly characterized.

Can BCG affect the results of a PPD skin test?

BCG vaccination may cause a positive reaction to the tuberculin skin test (TST), which may complicate decisions about prescribing treatment.

Should you get a PPD If you have had the BCG vaccine?

TB infection can be diagnosed with two types of tests: a TB skin test (TST), also called a PPD; and one of two blood tests, called IGRAs. We recommend a blood test for anyone who has had a BCG vaccination.

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Can BCG cause positive Mantoux test?

A false positive result may be caused by nontuberculous mycobacteria or previous administration of BCG vaccine. Vaccination with BCG may result in a false-positive result for many years after vaccination. False positives can also occur when the injected area is touched, causing swelling and itching.

Why does the tuberculosis vaccine leave a scar?

Why did scarring occur? Scars like the smallpox vaccine scar form due to the body’s natural healing process. When the skin is injured (like it is with the smallpox vaccine), the body rapidly responds to repair the tissue.

Can you test positive for TB if you had the vaccine?

The BCG vaccine is not very good at protecting adults against TB. You can still get TB infection or TB disease even if you were vaccinated with BCG. You will need a TB test to see if you have latent TB infection or TB disease.

How common is a false positive TB skin test?

In 18 studies involving 1,169,105 subjects, the absolute prevalence of false-positive TST from NTM cross-reactivity ranged from 0.1\% to 2.3\% in different regions. Conclusions: The effect on TST of BCG received in infancy is minimal, especially > or =10 years after vaccination.

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How do I know if I had the TB vaccine?

TB blood tests are the preferred method of TB testing for people who have received the BCG vaccine.

Why would a TB test be false positive?

The causes of these false-positive reactions may include, but are not limited to, the following: Previous TB vaccination with the bacille Calmette-Guérin (BCG) vaccine. Infection with nontuberculosis mycobacteria (mycobacteria other than M. tuberculosis)

Can a positive TB blood test be wrong?

The test might show you don’t have TB when you do, especially if you were exposed a long time ago and your immune response to it is weak. Or you could get a false positive result if you’ve been vaccinated with the TB bacillus Calmette-Guerin (BCG) vaccine.