Topic Review: Screening for Latent Tuberculosis (LTB).   Author: Peter R. McNally, DO, FACP, FACG

Center for Human SimulationUniversity of Colorado – Denver, SOM

Topic Review: Screening for Latent Tuberculosis (LTB).   Author: Peter R. McNally, DO, FACP, FACG

Center for Human SimulationUniversity of Colorado – Denver, SOM

Tables & Figures

McNally.VHJOE.TR.TB.2010.N0.3

Table 1. Digestive and Hepatic Disorders Requiring Immune Suppression TherapyTable 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 TSTTable 2. High Risk Groups Cutoffs for (+) Mantoux TST

Measured Induration

High Risk Group Positive TST

> 5 mm Recent Contact with TB case Yes

HIV-positive person Yes

Abn Chest x-ray (Nodular or Fibrotic Δ) Yes

Organ Transplant Recipient Yes

On Immunosuppressant Medication

> 15 mg/day Prednisone, for > 1 month Yes

> 2 mg/kg/day of azathioprine Yes

> 1 mg/kg/day of 6-mercaptopurine Yes

> 25 mg/week of methotrexate Yes

Any anti-TNF-α medication yes

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

Measured Induration

Moderate Risk Group Positive TST

> 10 mm Residents and employees of high-risk congregate settings (prisons, nursing homes, hospitals, homeless shelters)

yes

IV Drug Users Yes

Mycobacteriology Laboratory personnel Yes

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

Table 4. Differences Between Currently Available INF-γ Release Assays

QFT-G QFT-GIT T-Spot

Sample Process Whole blood< 12 hrs

Whole blood < 16 hrs

Peripheral monocytes (PB-MCs) < 8 hrs

M. tuberculosis Antigen

Separate MixtureESAT-6 CFP-10

Single MixtureESAT-6CFP-10TB7.7

Separate MixtureESAT-6CFP-10

Measurement INF-γ concentration

INF-γ concentration

No INF-γ producing cells

Possible Results PositiveNegativeIndeterminate

PositiveNegativeIndeterminate

PositiveNegativeIndeterminateBorderline

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

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

TST INF-γ Release Assay

No. of Patient Office Visits 2 1

Results available within 24 hr No Yes

Subject to reader bias Yes No

False (+) with prior BCGImmunization or chemotherapy

Yes No

False (-) with immune suppression

Yes “No”

Can “boost” immune response on subsequent testing

Yes No

Table 6. CDC Guidance on Selection of TST or IGRATable 6. CDC Guidance on Selection of TST or IGRA

Situations 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 poor IGRA indeterminate, TST may be helpful

Figure 1. Estimated TB incidence rates, 2008Figure 1. Estimated TB incidence rates, 2008

http://whqlibdoc.who.int/publications/2009/9789241598866_eng.pdf

Figure 2. Mantoux TSTFigure 2. Mantoux TST

A. Intra-dermal PPD InjectionB. Size of induration, not erythrema should be measured.

http://en.wikipedia.org/wiki/File:Mantoux_test.jpg