2 step TB test

Baseline Testing: Two-Step Test

Two-step testing with the Mantoux tuberculin skin test (TST) should be used for baseline or initial testing.  Some people with latent TB infection have a negative reaction when tested years after being infected.  The first TST may stimulate or boost a reaction.  Positive reactions to subsequent TSTs could be misinterpreted as a recent infection.

Step 1

  • Administer first TST following proper protocol
  • Review result
    • Positive — consider TB infected, no second TST needed; evaluate for TB disease.
    • Negative — a second TST is needed.  Retest in 1–3 weeks after first TST result is read.
  • Document result

Step 2

  • Administer second TST 1-3 weeks after first test
  • Review results
    • Positive — consider TB infected and evaluate for TB disease.
    • Negative — consider person not infected.
  • Document result

Two-Step TST Testing

Blood Test vs Skin Test…

If you are going to struggle to go back for a follow up appointment for the TST then the blood test will be best as only one test is required and the results are given electronically.

False positives can occur in a TST if you have had a BCG.

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