PPD (TB Skin Test) or Interferon-Gamma Release Assay (TB Blood Test)?

A recent editorial (JG Hashash et al. Inflamm Bowel Dis 2020; 26: 1315-1318Approach to Latent Tuberculosis Infection Screening Before Biologic Therapy in IBD Patients: PPD or IGRA?) provides some guidance on screening for tuberculosis prior to biologic therapy as well as background on how these tests work.

Key points:

  • The authors state that both a PPD or TB Blood Test (aka Quantiferon-TB Gold) are reasonable for most individuals, though they have a preference for the TB Blood Test.
  • For those with history of BCG vaccination, the TB Blood Test is recommended
  • Steroids are associated with negative PPD and indeterminate TB Blood Test.
  • The authors advocate baseline testing prior to biologic therapy for everyone.
  • Annual testing: For  those in high TB endemic areas, “we propose yearly chest x-ray in addition to IGRA [TB Blood Test]…in low endemic areas…we do not perform yearly chest x-rays nor do we check yearly IGRA unless mandated by a patient’s insurance.”

My take: TB blood testing is more convenient but more costly.  The authors indicate that  for patients from low endemic areas, yearly TB testing is mainly to check boxes mandated by insurance companies rather than improving care.

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