Editing Mantoux test (section)

==False positive result==
TST (tuberculin skin test) positive is measured by size of induration. The size of the induration considered to be a positive result depends on risk factors. For example, a low-risk patient must have a larger induration for a positive result than a high-risk patient. High-risk groups include recent contacts, those with HIV, those with chest [[radiograph]] with fibrotic changes, organ transplant recipients, and those with immunosuppression.{{cn|date=May 2024}}

A meta-analysis in 2014 found that the [[BCG vaccine|Bacillus Calmette–Guérin (BCG) vaccine]] reduced infections by 19–27% and reduced progression to active tuberculosis by 71%.<ref name="pmid25097193">{{cite journal | vauthors = Roy A, Eisenhut M, Harris RJ, Rodrigues LC, Sridhar S, Habermann S, Snell L, Mangtani P, Adetifa I, Lalvani A, Abubakar I | title = Effect of BCG vaccination against Mycobacterium tuberculosis infection in children: systematic review and meta-analysis | journal = BMJ | volume = 349 | pages = g4643 | date = August 2014 | pmid = 25097193 | pmc = 4122754 | doi = 10.1136/bmj.g4643 }}</ref> The Ohio Department of Health states that it give 80% of children protection against [[tuberculous meningitis]] and [[miliary tuberculosis]]. Therefore, a positive TST/PPD in a person who has received BCG vaccine is interpreted as latent TB infection (LTBI).<ref>Information also from ODH lecture at the Ohio State University 5/24/2012.</ref>
Due to the test's low specificity, most positive reactions in low-risk individuals are false positives.<ref name="pmid8668383">{{cite journal | author=Starke JR | title=Tuberculosis Skin Testing: New Schools of Thought|date=Jul 1996 | journal=Pediatrics | volume=98 | issue=1 | pages=123–125 | doi=10.1542/peds.98.1.123| issn=0031-4005 | pmid=8668383 | s2cid=19907614}}</ref> A false positive result may be caused by [[nontuberculous mycobacteria]] or previous administration of BCG vaccine.  Vaccination with BCG may result in a false-positive result for many years after vaccination.<ref>{{cite journal |vauthors=Chaturvedi N, Cockcroft A | title=Tuberculosis screening among health service employees: who needs chest X-rays? | year=1992 | journal=J Soc Occup Med | volume=42 | pages=179–82  | doi = 10.1093/occmed/42.4.179 | pmid=1421331 | issue=4}}</ref>

False positives can also occur when the injected area is touched, causing swelling and itching. If the swelling is less than 5&nbsp;mm, it is possibly due to error by the healthcare personnel causing inflammation to the area.{{cn|date=May 2024}}

Another source of false positive results can be allergic reaction or [[hypersensitivity]]. Although rare (about 0.08 reported reactions per million doses of tuberculin), these reactions can be dangerous and precautions should be taken by having [[epinephrin]] available.<ref>{{cite journal |author1=James E. Froeschle |author2=Frederick L. Ruben |author3=A. Michael Bloh | title=Immediate Hypersensitivity Reactions after Use of Tuberculin Skin Testing| year=2002 | journal=Clinical Infectious Diseases | volume=34 | pages=e12–e13 | doi = 10.1086/324587 |pmid=11731966 | issue=1| doi-access=free }}</ref>