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:
“False opinions are like false money, struck first of all by guilty men and thereafter circulated by honest people who perpetuate the crime without knowing what they are doing.”
—Joseph De Maistre (1753–1821)
“Regna regnis lupi, The State is a wolf unto the State. It is not a pessimistic lamentation like the old homo homini lupus [Man is a wolf to Man], but a positive creed and political ideal.”
—Johan Huizinga (1872–1945)
“A great number of the disappointments and mishaps of the troubled world are the direct result of literature and the allied arts. It is our belief that no human being who devotes his life and energy to the manufacture of fantasies can be anything but fundamentally inadequate”
—Christopher Hampton (b. 1946)