Topic Review: Screening for Latent Tuberculosis (LTB). Author: Peter R. McNally, DO, FACP, FACGCenter for Human SimulationUniversity of Colorado Denver, SOM

Tables & FiguresMcNally.VHJOE.TR.TB.2010.N0.3

Table 1. Digestive and Hepatic Disorders Requiring Immune Suppression TherapyCrohns DiseaseUlcerative colitisAutoimmune HepatitisRecipient of Organ Transplantation

Table 2. High Risk Groups Cutoffs for (+) Mantoux TST

Measured IndurationHigh Risk GroupPositive TST> 5 mmRecent Contact with TB caseYesHIV-positive personYesAbn Chest x-ray (Nodular or Fibrotic )YesOrgan Transplant RecipientYesOn 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- medicationyes

Table 3. Moderate Risk Groups Cutoffs for (+) Mantoux TST

Measured IndurationModerate Risk GroupPositive TST> 10 mmResidents and employees of high-risk congregate settings (prisons, nursing homes, hospitals, homeless shelters)yesIV Drug UsersYesMycobacteriology Laboratory personnelYesMedical Conditions: silicosis, diabetes mellitus, chronic renal failure, significant weight loss > 10% of IBW, prior gastrectomy or jejunoileal bypass, and leukemiaYesChildren < 4 yrs of age or children exposed to adults in high-risk categoryYesRecent immigrants (

Table 4. Differences Between Currently Available INF- Release Assays

QFT-GQFT-GITT-SpotSample ProcessWhole blood< 12 hrsWhole blood < 16 hrsPeripheral monocytes (PB-MCs) < 8 hrsM. tuberculosis AntigenSeparate MixtureESAT-6 CFP-10Single MixtureESAT-6CFP-10TB7.7Separate MixtureESAT-6CFP-10MeasurementINF- concentrationINF- concentrationNo INF- producing cells

Possible ResultsPositiveNegativeIndeterminatePositiveNegativeIndeterminatePositiveNegativeIndeterminateBorderline

Table 5. Comparison of LTB DetectionWith TST and INF- Release Assay

TSTINF- Release AssayNo. of Patient Office Visits21Results available within 24 hrNoYes Subject to reader biasYesNoFalse (+) with prior BCGImmunization or chemotherapyYesNoFalse (-) with immune suppressionYesNoCan boost immune response on subsequent testingYesNo

Table 6. CDC Guidance on Selection of TST or IGRASituations IGRA is preferred, but a TST is acceptableTesting persons with poor TST 48 hr return ratesPreviously BCG vaccine or cancer therapy

Situations TST is preferred, but IGRA is acceptableChildren < 5 yrs (some experts require both TST & IGRA)

Situations where No Preference TST = IGRA Recent contacts of MTBMTB Screening & Surveillance Programs

Situations Both IGRA and TST may be consideredWhen either test (-) and risk for MTB high and outcome poorIGRA indeterminate, TST may be helpful

Figure 1. Estimated TB incidence rates, 2008http://whqlibdoc.who.int/publications/2009/9789241598866_eng.pdf

Figure 2. Mantoux TSTA. Intra-dermal PPD InjectionB. Size of induration, not erythrema should be measured.http://en.wikipedia.org/wiki/File:Mantoux_test.jpg