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)
“People who talk about revolution and class struggle without referring explicitly to everyday life, without understanding what is subversive about love and what is positive in the refusal of constraints, such people have a corpse in their mouth.”
—Raoul Vaneigem (b. 1934)
“It is the custom of the immortal gods to grant temporary prosperity and a fairly long period of impunity to those whom they plan to punish for their crimes, so that they may feel it all the more keenly as a result of the change in their fortunes.”
—Julius Caesar [Gaius Julius Caesar] (100–44 B.C.)