Can a Tuberculosis (TB) test be performed on a patient with a fever from another infection?

Can a TB Test Be Done While a Patient Has a Fever from Another Infection?

Yes, a tuberculin skin test (TST/PPD) can be administered to a patient with fever from another infection, but the result may be falsely negative and should be interpreted with caution, particularly if the fever indicates acute illness or severe infection. 1

Key Considerations for Testing During Febrile Illness

Factors That May Cause False-Negative Results

The tuberculin skin test has a documented false-negative rate of approximately 25% during initial evaluation of persons with active tuberculosis, with this high rate attributed to poor nutrition, general health status, or overwhelming acute illness. 1

Specific infections that can suppress tuberculin reactivity include:

• Viral infections (measles, mumps, chickenpox, HIV) 1
• Bacterial infections (typhoid fever, brucellosis, typhus, leprosy, pertussis, overwhelming tuberculosis) 1
• Fungal infections (South American blastomycosis) 1
• Metabolic derangements associated with acute illness 1

Clinical Decision-Making Algorithm

For high-priority contacts (children <5 years, HIV-infected, immunocompromised):

• Administer the TST at initial encounter regardless of fever status 1
• If the patient has acute febrile illness, document this condition 1
• Plan for repeat testing 8-10 weeks after exposure ends to account for both the window period and potential false-negative from acute illness 1

For medium and low-priority contacts:

• If fever is from mild, self-limited infection: proceed with testing 1
• If fever indicates severe acute illness or immunosuppression: consider delaying initial test until recovery, or proceed with testing but plan mandatory repeat testing 1

Important Timing Considerations

The window period for tuberculin reactivity is 8-10 weeks after exposure to M. tuberculosis, meaning a negative test obtained less than 8 weeks after exposure is unreliable regardless of fever status. 1 Therefore, repeat testing at 8-10 weeks post-exposure is already recommended for contacts, which provides an opportunity to retest after resolution of the concurrent febrile illness. 1

Practical Approach

The test can and should be administered during the initial encounter even with fever present, but with the following caveats:

1. Document the concurrent illness - Record the presence of fever and the suspected or confirmed diagnosis causing the fever 1

2. Lower your threshold for repeat testing - Any negative result in a febrile patient should prompt repeat testing after both the acute illness resolves AND the 8-10 week window period has elapsed 1

3. Do not delay evaluation of symptomatic contacts - Diagnostic evaluation of any contact with TB symptoms should be immediate, regardless of skin test results or concurrent fever 1

4. Consider alternative testing - In severely immunocompromised or acutely ill patients where false-negative TST is highly likely, interferon-gamma release assays (IGRAs) may be considered, though these can also be affected by acute illness 2, 3

Common Pitfalls to Avoid

• Do not assume a negative TST rules out TB infection in a febrile patient - The sensitivity is too low in acute illness 1
• Do not delay testing in high-priority contacts - The risk of missing early infection outweighs concerns about false-negatives, as repeat testing is already indicated 1
• Do not forget to retest - A single negative test in the setting of fever and recent exposure is insufficient 1
• Do not use TST results alone to diagnose or exclude active TB disease - Clinical evaluation, chest radiography, and sputum examination remain essential regardless of TST results 4