Latent Tuberculosis Infection (LTBI)

Who to Screen

1. Pts likely to be infected w/ Mtb
2. Pts at hi risk of active TB if infected
See TB — Overview
DO NOT SCREEN:  Persons w/o any of above risks

How to Screen  —  Either of the following:

1. Purified Protien Derivative (PPD):
  • Pos = 10 mm induration read at 48-72 hrs
  • 10 mm Induration >72 hrs also pos
  • Vesicles always Pos [even w/o 10 mm induration]
  • 5 mm = Pos if: HIV, abnl CXR, or recent contact w/ active TB pt
  • Ignore Hx BCG vaccine when interpreting
2. Interferon Gamma Release Assay (IGRA)
  • Brand Names: QuantiFERON® and T-Spot.TB®
  • Equal sensitivity w/ PPD
  • If result “indeterminate,” test is uninterpretable [place PPD]

Positive PPD or IGRA  Obtain CXR

  • If “normal,” Dx LTBI
  • If only a “calcified granuloma,” Dx LTBI
  • Other findings need W/U (cavities, infiltrates, nodules, “fibrotic scars”)
1.  If Dx LTBI:
  • Teach pt to never get another test
  • Repeat CXRs unnecessary unless symptomatic, or required by job
  • Persons with LTBI may be candidates for INH Tx
2.  Work-Up for Abnormal CXR plus Pos. PPD / IGRA
  • Best performed by TB Control at Health Dept.
  • If Sx suggestive of Active TB, needs treatment for such
  • If completely Asymptomatic: order Sputum for AFB
    • 3 days in a row, early AM collection
  • Wait 60 days for Sputum Results.  If Neg → repeat CXR
  • If CXR “stable” (no change), Dx “TB-4” [i.e. “Old Scar”]
    • Tx w/ INH for full 9 mos.

See postings TB -1 (Intro) and TB-2 (Latent TB)