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Quick Reference on TB Skin Testing

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					                                 Quick Reference on TB Skin Testing:
                                                    2-step vs. contact follow-up

      How to do a skin test                                          Who should get a 2-step skin test?
      • Administer 0.1 mL of 5 tuberculin units (5-TU) of            People who are beginning a schedule of skin testing at
        purified protein derivative (PPD), injected intradermally    regular intervals should have a 2-step as their initial test.
        on volar aspects of the forearm.2                            • Health care professionals.
      • If no weal appears, inject another 0.1 mL of PPD 5 cm        • Corrections staff.
        from the previous site or in the other arm.1
                                                                     • Travellers who are going to an area with a high
      • Record the time, date, lot number, expiry date and             prevalence of TB for 1 month or more.2
        dose of PPD injected and the site(s) of injection.3
                                                                     • Residents of long-term care facilities.
      • Patients should wait 15 minutes after injection to
        monitor signs of anaphylaxis.                                • Shelter staff.3
      • Tests should be read and recorded after 48 to 72 hours
        by a trained health professional.2
      • Measure induration not erythema across the width of
                                                                     How to do a 2-step skin test
        the arm (i.e. transverse to the long axis of the forearm)    • Administer 0.1 mL of 5-TU of PPD intradermal as usual
        and record in mm.2                                             for each test.2
      Contraindications for skin test:                               • If the reaction on first skin test is negative, a second
                                                                       skin test is administered 1 to 4 weeks later.2
      • Patients with documented active TB or a clear history
        of treatment for TB infection or disease.                    • If the reaction on the first skin test is positive, a
                                                                       second skin test should not be administered.
      • Patients with severe blistering tuberculin reactions in
        the past.                                                    • If either the first or second skin test is positive, the
                                                                       person should be evaluated further to rule out active
      • Patients with extensive burns or eczema.                       TB disease (i.e. medical evaluation re: risk factors for
      • Patients with major viral infections or live-virus             TB, chest radiography, and in presence of symptoms,
        vaccinations in the past month e.g., MMR.                      sputum for acid fast bacilli smear and culture).
                                                                     • For people on a regular TB screening schedule, only
      A skin test may be administered before, on the same day          the initial round of testing needs to be 2-step. Once
      or 30 days after a live-virus vaccination e.g., MMR.1            baseline is established, subsequent routine testing
                                                                       (i.e. annually) is 1-step only.
      Not a contraindication for skin test:
      • Pregnancy.
      • Patients with a history of Bacille Calmette-Guerin           Skin testing for patients who are
        (BCG) vaccination.2
                                                                     contacts of an active TB case
                                                                     • Administer 0.1 mL of 5-TU of PPD intradermal as usual
      Why do a 2-step skin test?                                       for each test.2
                                                                     • Perform an initial skin test as soon as exposure to an
      • Assists in establishing a true baseline result for people
                                                                       active case of TB is identified.
        who will be getting serial TB skin tests.
                                                                     • Conversion of a skin test from negative to positive
      • A positive skin test may gradually wane over the
                                                                       after exposure to an active case may take 8 to12
        years. The initial skin test completed as part of the
                                                                       weeks. Therefore if the reaction on the first skin test is
        2-step process may stimulate the immune response,
                                                                       negative, administer a second skin test 8 to12 weeks
        and a positive reaction may occur when the person is
                                                                       after the contact’s last possible exposure to the active
        retested 1 to 4 weeks later. This delayed response is
                                                                       case.2
        called the booster phenomenon.2
                                                                     • If the reaction on the first skin test is positive, a
      • If a baseline is not measured through 2-step skin testing,
                                                                       second skin test should not be administered.
        a positive skin reaction on subsequent tests may be
        interpreted as a conversion (i.e. recent TB infection),
        when in fact the positive skin reaction may represent
        the booster phenomenon (i.e. previous TB infection).
                                                                                                                          over
February 2006
                           Quick Reference on TB Skin Testing (cont’d)

      • If either the first or second skin test is positive, the      Reporting requirements
        person should be evaluated further to rule out active
        TB disease (i.e. medical evaluation re: risk factors for
        TB, chest radiography, and in presence of symptoms,           All persons with a positive skin test must be
        sputum for acid fast bacilli smear and culture).2
                                                                      reported to Public Health.
      • There is no indication for 2-step skin testing for a
        contact of active TB. Skin test conversion can occur
        as early as 2 weeks. It is difficult to differentiate true    TB medications for prophylaxis and treatment are free
        conversion from the booster phenomena. Any change             through Public Health.
        in skin test reactivity must be considered as a true
        conversion.2
                                                                      Toronto Public Health
      • Contacts are identified by Public Health and provided
        with documentation for further follow-up from their           TB Prevention Team
        physicians.                                                   General inquiries . . . . . . . . . . . . . . . . . . . . . . . .416-392-7420
                                                                      Drug Order Line . . . . . . . . . . . . . . . . . . . . . . . . .416-392-7173
                                                                      Homeless/Underhoused Outreach Team . . . .416-392-7414
      How to interpret a TB skin test                                 TB Case Contact Management/Directly Observed
                                                                      Therapy Teams
         Tuberculin              Setting in which reaction            East Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . .416-338-7492
        Reaction Size             considered significant              North Region . . . . . . . . . . . . . . . . . . . . . . . . . . . .416-338-8380
      (mm of induration)      (meaning probable TB infection)         South Region . . . . . . . . . . . . . . . . . . . . . . . . . . .416-392-7420
                                                                      West Region . . . . . . . . . . . . . . . . . . . . . . . . . . . .416-338-1521
                0–4          HIV infection AND expected risk of
                             TB infection is high (e.g., patient is
                             immigrant from country where TB is       TB Clinics
                             endemic, is a household contact          Hospital for Sick Children
                             or has an abnormal radiograph).*         555 University Ave, main floor . . . . . . . . . . . . .416-813-8327
                             This reaction size is not normally
                             considered significant, but in the       St. Michaels Hospital
                             presence of immune suppression           30 Bond St, 6th floor, Queen Wing . . . . . . . . .416-864-6060
                             may be important.                         . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ext. 2673
                                                                      Toronto Western Hospital
                5–9          HIV infection.*                          399 Bathurst St, 8th floor, New East Wing . .416-603-5853
                             Close contact of active
                             contagious case.                         West Park Healthcare Centre
                             Abnormal chest radiograph with           82 Buttonwood Ave, 2 east B . . . . . . . . . . . . . .416-243-3600
                             fibronodular disease.                     . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ext. 2180

                                                                      References
                ≥ 10         All others.
                                                                      1
                                                                          Aventis Pasteur. (2000). Tuberculin Skin Test Guidelines.
      * All clients with HIV are high risk and should be seen         2
                                                                          Canadian Lung Association. (2000). Canadian Tuberculosis
        by a TB clinic.                                                   Standards. (5th ed.). Ottawa: Canadian Lung Association.
                                                                      3
                                                                          Ontario Ministry of Health and Long Term Care. (1998).
                                                                          Ontario Ministry of Health Tuberculosis Protocol.
      Skin test results should be recorded in mm of induration,
      not simply as “positive” or “negative”.2
                                                                      If you have any questions, please contact the
      Erythema should not be included in the measurement of
      a skin test. Redness does not indicate TB infection.2           TB Prevention Program at 416-392-7420 or
                                                                      targettb@toronto.ca
      Store PPD preparation between 2 and 8 degrees Celsius.
      Date the vial of tuberculin when first opened. Discard a        www.toronto.ca/health/tb_prevention
      vial of tuberculin preparation that has been opened and
      used after 1 month, as potency may be reduced.3

February 2006

				
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