Topic Review: Screening for Latent Tuberculosis (LTB). Author: Peter R. McNally, DO, FACP, FACG Center for Human Simulation University of Colorado – Denver, SOM Tables & Figures McNally.VHJOE.TR.TB.2010.N0.3

Table 1. Digestive and Hepatic Disorders Requiring Immune Suppression Therapy  Crohn’s Disease  Ulcerative colitis  Autoimmune Hepatitis  Recipient of Organ Transplantation

Table 2. High Risk Groups Cutoffs for (+) Mantoux TST Measured Induration High Risk GroupPositive TST > 5 mmRecent Contact with TB caseYes HIV-positive personYes Abn Chest x-ray (Nodular or Fibrotic Δ)Yes Organ Transplant RecipientYes On Immunosuppressant Medication > 15 mg/day Prednisone, for > 1 monthYes > 2 mg/kg/day of azathioprineYes > 1 mg/kg/day of 6-mercaptopurineYes > 25 mg/week of methotrexateYes Any anti-TNF-α medicationyes

Table 3. Moderate Risk Groups Cutoffs for (+) Mantoux TST Measured Induration Moderate Risk GroupPositive TST > 10 mmResidents and employees of high-risk congregate settings (prisons, nursing homes, hospitals, homeless shelters) yes IV Drug UsersYes Mycobacteriology Laboratory personnelYes Medical Conditions: silicosis, diabetes mellitus, chronic renal failure, significant weight loss > 10% of IBW, prior gastrectomy or jejunoileal bypass, and leukemia Yes Children < 4 yrs of age or children exposed to adults in high-risk category Yes Recent immigrants (<5 yrs) from high prevalence countries yes

Table 4. Differences Between Currently Available INF-γ Release Assays QFT-GQFT-GITT-Spot Sample ProcessWhole blood < 12 hrs Whole blood < 16 hrs Peripheral monocytes (PB-MCs) < 8 hrs M. tuberculosis Antigen Separate Mixture ESAT-6 CFP-10 Single Mixture ESAT-6 CFP-10 TB7.7 Separate Mixture ESAT-6 CFP-10 MeasurementINF-γ concentration No INF-γ producing cells Possible ResultsPositive Negative Indeterminate Positive Negative Indeterminate Positive Negative Indeterminate Borderline

Table 5. Comparison of LTB Detection With TST and INF-γ Release Assay TSTINF-γ Release Assay No. of Patient Office Visits21 Results available within 24 hrNoYes Subject to reader biasYesNo False (+) with prior BCG Immunization or chemotherapy YesNo False (-) with immune suppression Yes“No” Can “boost” immune response on subsequent testing YesNo

Table 6. CDC Guidance on Selection of TST or IGRA  Situations IGRA is preferred, but a TST is acceptable Testing persons with poor TST 48 hr return rates Previously BCG vaccine or cancer therapy  Situations TST is preferred, but IGRA is acceptable Children < 5 yrs (some experts require both TST & IGRA)  Situations where No Preference TST = IGRA Recent contacts of MTB MTB Screening & Surveillance Programs  Situations Both IGRA and TST may be considered When either test (-) and risk for MTB high and outcome poor IGRA indeterminate, TST may be helpful

Figure 1. Estimated TB incidence rates,

Figure 2. Mantoux TST A. Intra-dermal PPD Injection B. Size of induration, not erythrema should be measured.