False Positive Result
TST positive is measured by size of induration. The measurement of the induration is determined to be positive depending on risk factors. For example, a low-risk patient must have a larger induration for a positive than a high-risk patient. High-risk groups include recent contact, HIV, chest radiograph with fibrotic changes, organ transplant recipient, and immunosuppression.
According to the Ohio Department of Health and US Department of Health, the BCG vaccine does not protect against TB infection. It does, though, give 80% of children protection against tuberculous meningitis and miliary tuberculosis. Therefore, a positive TST/PPD in a person who received BCG vaccine is interpreted as latent TB infection (LTBI). Due to the test's low specificity, most positive reactions in low-risk individuals are false positives. A false positive result may be caused by nontuberculous mycobacteria or previous administration of BCG vaccine. Prior vaccination with BCG may result in a false-positive result for many years afterwards.
False positives can also occur when the injected area is touched, causing swelling and itching.
Read more about this topic: Mantoux Test
Famous quotes containing the words false, positive and/or result:
“If I should go out of church whenever I hear a false statement I could never stay there five minutes. But why come out? The street is as false as the church, and when I get to my house, or to my manners, or to my speech, I have not got away from the lie.”
—Ralph Waldo Emerson (1803–1882)
“Property is the fruit of labor—property is desirable—is a positive good in the world.”
—Abraham Lincoln (1809–1865)
“Morals are in all countries the result of legislation and government; they are not African or Asian or European: they are good or bad.”
—Denis Diderot (1713–1784)