Can a Mantoux (tuberculin skin test) be performed on a patient who has received intravesical Bacillus Calmette-Guérin (BCG)?

Can a Mantoux Test Be Performed After Intravesical BCG?

Yes, a Mantoux tuberculin skin test (TST) can be performed on patients who have received intravesical BCG therapy, though the results must be interpreted with caution as the test may be positive due to BCG exposure rather than tuberculosis infection. 1

Key Principles for Testing

BCG Does Not Contraindicate Tuberculin Testing

• Previous BCG vaccination (including intravesical BCG) is not a contraindication to tuberculin skin testing. 1
• The FDA-approved tuberculin test (TUBERSOL) specifically states that prior BCG vaccination does not preclude performing the Mantoux test 1
• The test can still be used to support or exclude the diagnosis of TB infection in BCG-exposed individuals 1

Interpretation Challenges After BCG Exposure

The critical issue is not whether the test can be done, but how to interpret positive results:

• There is no reliable method to distinguish tuberculin reactions caused by BCG vaccination from those caused by natural Mycobacterium tuberculosis infection 2
• Intravesical BCG can induce tuberculin sensitivity similar to intradermal BCG vaccination 2
• The mean reaction size among persons who have received BCG is often <10 mm 2

Interpretation Guidelines After BCG Exposure

When to Consider a Positive Result as True TB Infection

It is prudent to consider "positive" reactions to 5 TU of PPD tuberculin in BCG-exposed persons as indicating infection with M. tuberculosis, especially in high-risk contexts: 2

Reasons to interpret positive TST as true TB infection rather than BCG effect:

• Tuberculin test conversion rates after BCG vaccination may be much less than 100% 2
• Tuberculin sensitivity from BCG tends to wane over time 2
• Most BCG-vaccinated persons are from high-prevalence areas where true TB infection is more likely 2

Standard Interpretation Thresholds Still Apply

Use risk-stratified interpretation even in BCG-exposed patients: 2, 3

• ≥5 mm induration: Positive for HIV-infected persons, recent TB contacts, immunosuppressed patients, or those with radiographic evidence of prior TB 2, 3
• ≥10 mm induration: Positive for persons from high TB prevalence countries, injection drug users, residents of high-risk congregate settings, or those with medical conditions increasing TB risk 2, 3
• ≥15 mm induration: Positive for persons with no known TB risk factors 2, 3

Alternative Testing Approach

For patients ≥5 years old with prior BCG exposure, an FDA-approved interferon-gamma release assay (IGRA) is preferred over tuberculin skin testing: 1

• IGRAs (such as QuantiFERON-TB Gold) are not affected by prior BCG vaccination 1
• This provides more specific results without the confounding effect of BCG exposure 1

Clinical Context for Intravesical BCG Patients

BCG Immunotherapy Does Not Predict TST Results

• A study of 823 bladder cancer patients receiving intravesical BCG found that Mantoux TST results did not correlate with BCG immunotherapy effectiveness or toxicity 4
• This suggests that intravesical BCG exposure creates variable tuberculin sensitivity, similar to intradermal BCG vaccination 4

Practical Approach

If tuberculin testing is needed in a patient with prior intravesical BCG:

1. Perform the standard Mantoux test (0.1 mL of 5-TU PPD intradermally) 2
2. Read at 48-72 hours and measure transverse diameter of induration in millimeters 2, 3
3. Interpret using standard risk-stratified thresholds, recognizing that positive results may reflect BCG exposure 2
4. Consider IGRA testing instead if the patient is ≥5 years old, as this eliminates BCG-related false positives 1
5. If TST is positive and clinical suspicion for active TB exists, proceed with chest radiography and further evaluation regardless of BCG history 2, 3

Important Caveats

• Although a positive TST due to BCG can wane over time, it can be "boosted" by serial testing 2
• For BCG-exposed individuals with some degree of induration on initial testing, a conversion to "positive" is defined as an increase in induration by ≥10 mm on subsequent tests 2
• The size of tuberculin reaction in BCG-exposed persons does not reliably distinguish between M. tuberculosis infection and prior BCG effect 3