Tuberculin skin test: Difference between revisions
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= Procedure = |
== Procedure == |
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* Place tuberculin intradermally |
* Place tuberculin intradermally |
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* But there's also a two-step that I have to look up |
* But there's also a two-step that I have to look up |
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= Interpretation = |
== Interpretation == |
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* ≥5mm if high risk or immunosuppressed |
* ≥5mm if high risk or immunosuppressed |
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* History of BCG vaccination ''does not'' change interpretation of result |
* History of BCG vaccination ''does not'' change interpretation of result |
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== False Positives == |
=== False Positives === |
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* Infection with nontuberculosis mycobacteria, including ''M. bovis'' |
* Infection with nontuberculosis mycobacteria, including ''M. bovis'' |
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* Incorrect bottle of antigen used |
* Incorrect bottle of antigen used |
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== False Negatives == |
=== False Negatives === |
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* Cutaneous anergy (anergy is the inability to react to skin tests because of a weakened immune system) |
* Cutaneous anergy (anergy is the inability to react to skin tests because of a weakened immune system) |
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* Incorrect interpretation of reaction |
* Incorrect interpretation of reaction |
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= See Also = |
== See Also == |
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* [http://tstin3d.com/en/calc.html TST in 3D] |
* [http://tstin3d.com/en/calc.html TST in 3D] |
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Revision as of 15:30, 17 August 2019
Procedure
- Place tuberculin intradermally
- Read it for area of induration at 48 hours
- But there's also a two-step that I have to look up
Interpretation
- ≥5mm if high risk or immunosuppressed
- HIV positive/immune suppressed: induration ≥5mm
- TB close contact/suggestive CXR: induration ≥5mm
- ≥10mm if medium risk or child ≥15mm if low risk (all others)
- Immigration from TB country within past 5 years: induration ≥10mm
- Healthcare workers/IVDU/LTC residents: induration ≥10mm
- Children <4 years: induration ≥10mm
- ≥15mm if low risk (all others), or increase in induration by ≥10mm in last two years
- History of BCG vaccination does not change interpretation of result
False Positives
- Infection with nontuberculosis mycobacteria, including M. bovis
- Previous BCG vaccination
- Incorrect method of TST administration
- Incorrect interpretation of reaction
- Incorrect bottle of antigen used
False Negatives
- Cutaneous anergy (anergy is the inability to react to skin tests because of a weakened immune system)
- Recent TB infection (within 8-10 weeks of exposure)
- Very old TB infection (many years)
- Very young age (less than 6 months old)
- Recent live-virus vaccination (e.g., measles and smallpox)
- Overwhelming TB disease
- Some viral illnesses (e.g., measles and chicken pox)
- Incorrect method of TST administration
- Incorrect interpretation of reaction
