What is the next step after a positive Tuberculin (TB) skin test?

Management of Positive TB Skin Test

The next step after a positive TB skin test is to obtain a chest radiograph to exclude active pulmonary tuberculosis, followed by evaluation for latent TB infection (LTBI) treatment if the chest X-ray is normal and no symptoms are present. 1

Immediate Diagnostic Evaluation

Chest Radiograph - The Critical First Step

• All persons with a positive tuberculin skin test require a chest radiograph to exclude active TB disease before any other management decisions are made. 2, 1
• The chest X-ray should be obtained promptly, even in asymptomatic individuals, as radiographic abnormalities may be present without symptoms 1
• For pregnant women with positive skin tests, chest radiographs with appropriate abdominal shielding should be performed as soon as feasible, even during the first trimester 1
• Children younger than 5 years should have both posterior-anterior and lateral chest radiographs 1

Clinical Assessment for Active TB

• Evaluate for symptoms suggestive of active TB including: productive cough lasting >2-3 weeks, weight loss, fever, night sweats, fatigue, and anorexia 3, 4
• If any symptoms consistent with TB are present, proceed immediately with diagnostic evaluation including sputum collection for acid-fast bacilli (AFB) smear and mycobacterial culture, regardless of chest X-ray findings. 2, 1

Interpretation Based on Chest X-ray Results

Normal Chest X-ray Without Symptoms

• If the chest radiograph is normal and no symptoms of active TB are present, the patient should be evaluated for treatment of latent tuberculosis infection (LTBI). 2, 1
• Treatment for LTBI is indicated to prevent progression to active disease 2, 5
• Standard treatment is isoniazid for 6-12 months, with 12 months recommended for HIV-infected individuals and those with fibrotic lesions on chest X-ray 5, 4

Abnormal Chest X-ray or Presence of Symptoms

• If the chest X-ray shows abnormalities or symptoms are present, further diagnostic evaluation is required including collection of at least three consecutive sputum specimens for AFB smear and culture. 2, 1, 4
• Typical radiographic findings suggestive of active TB include upper lobe infiltration (particularly with cavitation), patchy or nodular infiltrates in apical or subapical posterior upper lobes 1
• For individuals with fibrotic lesions suggesting old healed TB, three consecutive sputum samples should be obtained even if asymptomatic 1

Special Populations Requiring Modified Approach

High-Risk Contacts and Recent Exposure

• For contacts of infectious TB cases with positive skin tests (≥5 mm induration), obtain chest radiograph immediately; if normal, initiate LTBI treatment. 2
• Children younger than 5 years and HIV-infected contacts require rapid evaluation to prevent serious complications like TB meningitis 2
• If the initial skin test was performed <8 weeks after last exposure, a repeat test at 8-12 weeks is necessary to detect delayed conversion 2

Immunocompromised Patients

• HIV-infected individuals with positive skin tests (≥5 mm) require chest radiograph and should receive 12 months of LTBI treatment if active disease is excluded 5
• Persons on prolonged corticosteroid therapy, immunosuppressive therapy, or with conditions like diabetes, silicosis, end-stage renal disease, or hematologic malignancies require evaluation with ≥10 mm induration 5

Previously Positive Skin Test

• Persons with documented prior positive tuberculin skin test who are not immunocompromised generally do not require further evaluation unless they have symptoms suggestive of TB disease. 2
• However, if they meet criteria for LTBI treatment based on other risk factors, they should receive medical evaluation including chest radiograph before treatment initiation 2

Treatment Considerations for LTBI

Indications for Preventive Therapy

The FDA-approved indications for isoniazid preventive therapy include 5:

• HIV-infected persons with ≥5 mm induration (12 months of therapy recommended) 5
• Close contacts of newly diagnosed infectious TB cases with ≥5 mm induration 5
• Recent converters (≥10 mm increase within 2 years for age <35; ≥15 mm increase for age ≥35) 5
• Persons with fibrotic lesions on chest X-ray suggesting old healed TB (≥5 mm induration, 12 months of therapy) 5
• IV drug users known to be HIV-seronegative with ≥10 mm induration 5
• Medical conditions increasing TB risk (≥10 mm): silicosis, diabetes, immunosuppressive therapy, end-stage renal disease, malignancies, chronic malnutrition 5

Age and Risk Factor Considerations

• Persons under age 35 from high-prevalence countries, medically underserved populations, or residents of long-term care facilities with ≥10 mm induration are candidates for preventive therapy 5
• Persons under age 35 with no risk factors but ≥15 mm induration are appropriate candidates 5
• For those over age 35, the risk of hepatitis from isoniazid must be weighed against TB risk, though treatment is recommended for those with additional risk factors 5

Common Pitfalls and Caveats

• Never rely on skin test results alone—chest radiograph is mandatory before any treatment decisions 1
• Do not measure erythema (redness) instead of induration (hardness)—only induration determines positivity 6
• Avoid testing individuals who do not require evaluation or who would not be candidates for treatment if positive 6
• For healthcare workers or those with repeat testing needs, failure to use two-step testing at baseline can lead to misinterpretation of boosted reactions as new infections 6
• Do not perform repeat chest radiographs routinely in asymptomatic persons with positive skin tests after initial evaluation—only if symptoms develop 2, 1
• BCG vaccination history should not prevent appropriate evaluation and treatment of positive skin tests 6