What tests are recommended for screening of Tuberculosis (TB)?

Tuberculosis Screening Tests

For TB screening, request either an interferon-gamma release assay (IGRA) or tuberculin skin test (TST), combined with a symptom evaluation and individual risk assessment; if testing is positive, obtain chest radiography to distinguish latent TB infection from active disease. 1, 2

Core Screening Components

The screening process consists of three essential elements that should be performed together:

1. Individual Risk Assessment

• All persons should receive a TB risk assessment before testing to properly interpret results 1, 2
• The assessment should identify: history of TB exposure, country of origin (particularly from high-burden countries in Africa, Asia, Eastern Europe, Latin America, and Russia), living/working conditions in congregate settings, immunosuppressive conditions, and HIV status 2
• This risk assessment is critical because it guides interpretation of positive test results and determines whether confirmatory testing is needed 1

2. Symptom Evaluation

• Screen for classic TB symptoms: cough lasting 2-3 weeks or longer, fever, night sweats, weight loss, and hemoptysis 1, 2
• Symptom screening should occur at baseline and whenever exposure is recognized 1
• In HIV-infected patients, also assess for unexplained cough and fever, as presentation may be atypical 1

3. Testing for M. tuberculosis Infection

• Perform either IGRA or TST in persons without documented prior latent TB infection (LTBI) or TB disease 1, 2
• IGRA is preferred over TST in patients with prior BCG vaccination, those already on immunosuppressive therapy, and situations where return for TST reading is unlikely 2
• Testing should only be performed in persons without documented prior LTBI or TB disease 1, 2

Interpretation of Positive Tests

For asymptomatic persons at low risk with a positive initial test, perform a second confirmatory test (either IGRA or TST); consider the person infected only if both tests are positive. 1, 2

After Positive Testing:

• Obtain chest radiography to distinguish latent TB infection from active TB disease 1, 2
• If chest X-ray suggests active TB, collect sputum specimens for acid-fast bacilli (AFB) microscopy and culture 1
• Chest radiography screening alone had 94% sensitivity and 73% specificity in prevalence surveys 3

High-Risk Populations Requiring Screening

Screen the following groups at baseline:

• Close contacts of persons with active pulmonary TB (household members and frequent visitors) 2
• Foreign-born persons from high TB burden countries 2
• Healthcare personnel at baseline prior to starting work 1, 2
• Persons living with HIV 1, 2
• Patients initiating immunosuppressive therapy (anti-TNF biologics, rituximab, corticosteroids) 2
• Patients preparing for organ or hematological transplantation 2
• Patients with chronic kidney disease or on dialysis 2
• Residents of congregate settings (correctional facilities, homeless shelters, long-term care facilities) 1, 2
• Persons with diabetes mellitus, malignancies, hepatitis C, rheumatoid arthritis, or vitamin D deficiency 2

Post-Exposure Screening Protocol

When exposure to infectious TB is recognized:

• Perform symptom evaluation immediately 1, 2
• Test with IGRA or TST at the time exposure is identified 1, 2
• If initial test is negative, repeat testing 8-10 weeks after last exposure using the same test type 1, 2
• Persons with documented prior LTBI or TB disease do not need repeat testing after exposure, but should have clinical evaluation if TB disease is suspected 1, 2

Common Pitfalls to Avoid

• Do not perform routine serial screening in low-risk healthcare settings; this is no longer recommended as of 2019 1
• Do not repeat IGRA or TST in persons who previously tested positive; instead, monitor for clinical signs and symptoms of active TB 2
• Do not skip the risk assessment; it is essential for proper interpretation of test results, particularly in asymptomatic persons with positive tests who may need confirmatory testing 1
• In HIV-infected patients, consider a tuberculin skin test positive when induration is ≥5mm 1

Follow-Up After Screening

Treatment is encouraged for all persons with untreated LTBI, unless medically contraindicated. 1, 2

• Preferred regimens include: isoniazid plus rifapentine once weekly for 3 months, isoniazid plus rifampin daily for 3-4 months, rifampin alone daily for 4 months, or isoniazid alone for 9 months 2
• For patients starting biologics including rituximab, initiate or resume biologic therapy after at least 1 month of LTBI treatment 2