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:
“Over the stark plain
The stilted mill-chimneys once again spread
Their sackcloth and ashes a flowing mane
Of repentance for the false day that’s fled.”
—William Robert Rodgers (1909–1969)
“Men just don’t “get” that the reason to become involved is for ourselves. Doing more with our children won’t simply make women happier or keep them “off our backs,” but will create a deeper, more positive connection with the kids.”
—Ron Taffel (20th century)
“A common and natural result of an undue respect for law is, that you may see a file of soldiers, colonel, captain, corporal, privates, powder-monkeys, and all, marching in admirable order over hill and dale to the wars, against their wills, ay, against their common sense and consciences, which makes it very steep marching indeed, and produces a palpitation of the heart.”
—Henry David Thoreau (1817–1862)