When given TST years after infection, these persons may have a false-negative reaction. However, the TST may stimulate the immune system, causing a positive or boosted reaction to subsequent tests. When sensitization to mycobacteria has occurred many years earlier, an initial intradermal injection of tuberculin may produce a negative or weakly positive response due to there being too few sensitized lymphocytes in circulation to produce a significant local response.
The second boosted reading is the correct one — that is, the result that should be used for decision-making or future comparison. Boosting is maximal if the second test is placed between one and five weeks after the initial test, and it may continue to be observed for up to two years.
Reversion is defined as the change to a negative Mantoux result following a previous positive result. Reversion is more common[ 13 ]. Whereas boosting is a recall of the hypersensitivity response in the absence of new Infection, conversion is the development of new or enhanced hypersensitivity due to infection with tuberculous or non-tuberculous mycobacteria, including BCG vaccination. Mantoux conversion is defined[ 14 ] as a change within a two-year period of Mantoux reactivity which meets either of the following criteria:.
There is debate about the time required for the immunological changes that produce Mantoux conversion following infection. After inadvertent vaccination with M. Other studies have shown clinical illness, with a positive tuberculin test, from 19 to 57 days after exposure, with a mean of 37 days. Therefore, when testing TB contacts for conversion, the second tuberculin test is done eight weeks after the date of last contact with the source case.
In the past, the traditional window period, or interval, of 12 weeks was used. There is disagreement about the role of Mantoux testing in people who have been vaccinated. Previous TB disease: no useful diagnostic information will be gained and significant discomfort is likely.
Infants under 12 weeks old: a positive reaction is very important, but a negative reaction may indicate that the child is too young to mount a response, and the test will need to be repeated if exposure has occurred. Pre-vaccination Mantoux testing before 12 weeks of age is not necessary unless the baby has been exposed to TB.
The Mantoux test is technically difficult to administer and read, so false readings may occur if the tester has insufficient skill. It may require four visits by the patient if a two-step test is performed, and compliance with this is sometimes difficult. A test that can be done on a single patient visit, such as a blood test, would be easier.
The blood test detects the presence of Mycobacterium tuberculosis TB infection by measuring interferon-gamma IFN-G harvested in plasma from whole blood incubated with the M.
This new immunodiagnostic test has been launched as an aid in the diagnosis of LTBI. It may be possible in future to replace the skin test with this, or an alternative in vitro assay. Source of Support: Nil. Conflict of Interest: None declared. National Center for Biotechnology Information , U. Indian Dermatol Online J.
Surajit Nayak and Basanti Acharjya. Author information Copyright and License information Disclaimer. Address for correspondence: Dr. E-mail: ni. This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.
This article has been cited by other articles in PMC. Abstract The tuberculin skin test is one of the few investigations dating from the 19 th century that are still widely used as an important test for diagnosing tuberculosis.
Keywords: Interpretation, Mantoux test, tuberculosis. End stage renal disease. Ten mm or more is positive in Recent arrivals less than five years from high-prevalence countries Injectable drug users Residents and employees of high-risk congregate settings e. Mycobacteriology lab personnel Persons with clinical conditions that place them at high risk e.
Children less than four years of age, or children and adolescents exposed to adults in high-risk categories Infants, children, and adolescents exposed to adults in high-risk categories. Fifteen mm or more is positive in Persons with no known risk factors for TB.
The causes of these false-positive reactions may include, but are not limited to, the following: Infection with non tuberculous mycobacteria Previous BCG vaccination Incorrect method of TST administration Incorrect interpretation of reaction Incorrect bottle of antigen used Due to the test's low specificity, most positive reactions in low-risk individuals are false-positives. False-negative result A negative Mantoux result usually signifies that the individual has never been exposed to M.
Table 1 Cutoff size of reaction for a positive Mantoux test in children. Open in a separate window. Menzies D. Tuberculin skin testing. Tuberculosis: A comprehensive international approach. New York: Marcel Dekker; Bevel-down superior to bevel-up in intradermal skin testing. Ann Allergy Asthma Immunol. American Thoracic Society. The tuberculin skin test, Am Rev Respir Dis. Diseases such as cancer and medications like steroids and chemotherapy that weaken your immune system may also cause a false-negative result.
Tuberculosis is a highly contagious bacterial disease. A positive tuberculosis TB skin test could look different from person to person.
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It does not mean you have TB disease active TB. When you are infected with TB bacteria you are not infectious and you cannot pass the bacteria onto other people. You are not sick but, at some stage in the future, you may develop TB disease. If you are told your TST is positive you may be asked to see a doctor for review. You will be given your result when you have the reading done.
If the result is negative, you may be advised that no further follow up is required. You may be recommended to have a repeat test in the future depending on why the test was initially performed. If the result is positive, you will require a chest X-ray and review by a medical officer. Some people with a latent TB will be offered medication to prevent them developing active TB. If your test is positive you may be advised not to have the test repeated.
The TST is a simple and safe test and side effects are uncommon. The side effects are mainly related to the size of the reaction and include swelling, redness and itchiness that may take a few weeks to clear. Very strong reactions are uncommon but may result in a painful swelling of several centimetres in size, blistering or ulceration. This will heal with almost no scarring. The effects of the TST are localised to the site and more general reactions are extremely rare.
This publication is provided for education and information purposes only. It is not a substitute for professional medical care. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your healthcare professional. Readers should note that over time currency and completeness of the information may change. All users should seek advice from a qualified healthcare professional for a diagnosis and answers to their medical questions.
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