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:
“The real essence, the internal qualities, and constitution of even the meanest object, is hid from our view; something there is in every drop of water, every grain of sand, which it is beyond the power of human understanding to fathom or comprehend. But it is evident ... that we are influenced by false principles to that degree as to mistrust our senses, and think we know nothing of those things which we perfectly comprehend.”
—George Berkeley (1685–1753)
“It is easy and dismally enervating to think of opposition as merely perverse or actually evil—far more invigorating to see it as essential for honing the mind, and as a positive good in itself. For the day that moral issues cease to be fought over is the day the word “human” disappears from the race.”
—Jill Tweedie (b. 1936)
“The only thing that one really knows about human nature is that it changes. Change is the one quality we can predicate of it. The systems that fail are those that rely on the permanency of human nature, and not on its growth and development. The error of Louis XIV was that he thought human nature would always be the same. The result of his error was the French Revolution. It was an admirable result.”
—Oscar Wilde (1854–1900)