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.