8 tuberculin skin test

8/9/2019 8 Tuberculin Skin Test

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Tuberculin Skin TestTuberculin Skin Test

( TST )( TST )

TheerakornTheerakorn TheerakittikulTheerakittikul, M.D., M.D.

Department of Internal medicine,Department of Internal medicine,

Faculty of Medicine, CMUFaculty of Medicine, CMU


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ObjectiveObjective

TechniqueTechnique

InterpretationInterpretation

Targeted testingTargeted testing

TreatmentTreatment


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ObjectiveO

bjective

The Test to find out Latent

Tuberculosis Infection (LTBI)


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TechniqueTechnique

Mantoux testMantoux test

Tuberculin

MultipleMultiple puncture testpuncture test

Tuberculin

Mantoux


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Administering the TST (MantouxMantoux test)test)

Inject 0.1 ml of 5 TU PPD

tuberculin solution

intradermally on volarsurface of lower arm

using a 27-gauge needle

Produce a wheal 6 to 10

mm in diameter


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Reading the TST

Measure reaction in 48 to 72 hours

Measure induration, not erythema

Record reaction in millimeters, not

negative or positive

Ensure trained health care

professional measures and interprets

the TST

InterpretationInterpretation


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Two - Step TT

If1st TT is < 10mm (negative)

2nd TT

should be done within 1wk - 5 wks

Booster Phenomenon


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Booster Phenomenon

Increased tuberculin reactions seen when a

second skin test is administrated 1 - 5 week

after the first skin test that is non-reactive.Represent an anamnestic of immune

response occurs in individuals with remote

exposure to mycobacterial antigens.

Magnus RI. Lancet19

55;24:643-4.


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0

5

10

15

20

0 0.1

mm

TimeTT1 TT2

Booster EffectTuberculin Test T T2 > 10mm

T T2 -T T1 > 6 mm


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TwoTwo--Step TestingStep Testing

A strategy to determine the difference betweenA strategy to determine the difference between

boosted reactions and reactions due to recentboosted reactions and reactions due to recent

infection.infection.

If first TST is positive, consider the personIf first TST is positive, consider the personhad ever infectedhad ever infected

If first TST is negative, give second TSTIf first TST is negative, give second TST 1155weeks laterweeks later

If second TST is positive, consider theIf second TST is positive, consider theperson had everperson had ever infectedinfected

If second TST is negative, consider theIf second TST is negative, consider the

person uninfected at baselineperson uninfected at baseline


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Two-Step Testing (2)

Use twoUse two--step tests for initial baselinestep tests for initial baselineskin testing of adults who will beskin testing of adults who will be

retested periodically (e.g., health careretested periodically (e.g., health careworkers,workers, residents of congregateresidents of congregate

settingssettings).).

TwoTwo--step testing is especially importantstep testing is especially importantwhen initially testing persons who havewhen initially testing persons who have

not had a test in the priornot had a test in the prior 1212 monthsmonths


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Indications forIndications for 22 step TSTsstep TSTs


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Recent converterRecent converter

Usefulness : if patient had previously

demonstrated to be true negative TST andfollow through some period of time (1-2

years) their TST convert to be positive

Represent TRUE new infectionRepresent TRUE new infection ::

These patient's got LTBIThese patient's got LTBI


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Tuberculin SkinTuberculin Skin TestTest

PreviousPrevious BCG vaccinationBCG vaccination

Tuberculin reactivity caused by BCGTuberculin reactivity caused by BCG

Generally wane with the passage of timeGenerally wane with the passage of time

Can be booster by the tuberculin skin testCan be booster by the tuberculin skin test

Periodic skin testing may prolong reactivityPeriodic skin testing may prolong reactivity

Reaction > 15 mm are not likely caused by BCGReaction > 15 mm are not likely caused by BCG


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False-Positive TST Reactions

Nontuberculous mycobacteria

Reactions caused by nontuberculous

mycobacteria are usually e 10 mm of induration

BCG vaccination

Reactivity in BCG vaccine recipients generally

wanes over time; positive TST result is likely dueto TB infection if risk factors are present


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False-Negative TST Reactions

Anergy

Inability to react to a TST because of a weakened

immune system (Immunocompromise stage)

Usefulness of anergy testing in TST-negative

persons who are HIV infected has not been

demonstrated

R

ecent TB infection Defined as 2 to 10 weeks after exposure

Very young age Newborns


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False-Negative TST Reactions-2

Live-virus vaccination

For example, measles or smallpox

Can temporarily suppress TST reactivity

Overwhelming TB disease

Poor TST administration technique

For example, TST injection too shallow ortoo deep, or wheal is too small


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Effect BCG : Tuberculin Reactivity

> 90 % of BCG vaccine recipients

TST > 10 mm within 8 -12 weeks after

Vaccine dose & BCG scar, Axillary LN.

Clear dose response relationship

1 year later : Vaccine dose & TST reactions

No relationship


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Waning Tuberculin Reactivity

After BCG Vaccination

Affected by age at vaccination

8 -12 weeks after : TST > 10mm

6 -12 months after : None had reaction > 10mm

10 - 25 years after : No different from non-BCG


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Criteria for TST positive (Criteria for TST positive (Induration, risk group), risk group)

Reaction >5 mm HIV positive

Recent contact

Fibrotic change onCXR (Old TB)

Organs transplant and

immunosuppressedstage

Reaction > 10 mm Immigrants within 5

yrs from highprevalence countries

Injection drug users

Residents andemployees of highrisk places

High risk clinicalsituations: silicosis,DM, CRF, leukemiasand lymphomas,carcinoma of thehead or neck andlung, weight loss of>10% ofIBW,gastrectomy, and

jejunoileal bypass

Reaction >15 mm Persons with no risk

factors for TB


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Targeted TestingTargeted Testing

TST

risk

LTBI


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Treatment of LTBI

8 tuberculin skin test

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