Tuberculosis Screening Test: Purpose, Test Details & Results

Tuberculosis (TB) remains a significant global health concern, affecting millions and posing a particular threat to high-risk groups, including immunosuppressed individuals and those living in crowded settings. Early detection is key to controlling the spread of TB and preventing progression from latent to active disease. In this article, we’ll explore why TB screening matters, the current and emerging tests available, and what your results might mean for you or your patients.

Purpose of Tuberculosis Screening Test

Screening for tuberculosis is about more than just preventing disease in individuals—it's a cornerstone of public health, aiming to identify and treat TB before it can be spread. Understanding who should be screened and why helps ensure resources are used effectively and that those at greatest risk receive timely care.

Table 1: Main Purposes of TB Screening

Why Screen for TB?

TB is contagious and primarily spreads through airborne droplets. Many people carry the bacteria without symptoms (latent TB infection, LTBI), but can develop active disease, especially when immunity is weakened. Screening identifies these silent carriers and helps prevent new cases by starting treatment early 1 9.

Who Should Be Screened?

Screening isn’t for everyone, but is crucial for:

• Close contacts of people with active TB
• Individuals with weakened immune systems (e.g., HIV, organ transplant recipients)
• Immigrants from high-prevalence countries
• Residents or workers in high-risk settings (prisons, shelters)
• Health care workers exposed to TB 1 8

Broader Public Health Impact

Community-wide screening, especially in high-prevalence regions, has been shown to lower TB rates and limit outbreaks. For example, in Vietnam, systematic screening dramatically reduced active TB prevalence in just three years 2. In environments like jails, screening can help identify undiagnosed cases, though ensuring follow-up after release remains a challenge 8.

Tuberculosis Screening Test Details

TB screening technology has evolved substantially, offering a range of tests varying in cost, complexity, and accuracy. Here’s a concise overview of the most widely used and emerging tests.

Table 2: Main TB Screening Test Types

Tuberculin Skin Test (TST)

• What is it?
  The TST, often called the Mantoux test, involves injecting a small amount of purified protein derivative (PPD) under the skin and checking for a reaction after 48–72 hours.
• Strengths:
  Inexpensive and widely available.
• Limitations:
  Can yield false positives in people vaccinated with BCG or exposed to non-TB mycobacteria, and false negatives in immunosuppressed individuals 1 7 9.

Interferon-Gamma Release Assays (IGRAs)

• What are they?
  Blood tests (e.g., QuantiFERON-TB Gold, T-SPOT.TB) that measure immune response to specific TB antigens.
• Strengths:
  More specific than TST, especially in BCG-vaccinated individuals. No need for a return visit.
• Limitations:
  Require laboratory infrastructure, are more expensive, and may yield indeterminate results in immunosuppressed patients 1 7 9 10.

C-Reactive Protein (CRP) and Symptom-based Screening

• What is it?
  Point-of-care blood test measuring inflammation; often combined with symptom screening in people living with HIV.
• Strengths:
  Rapid, low-cost, and effective at ruling out active TB in high-risk populations.
• Limitations:
  Not specific to TB—can be elevated in many conditions. Sensitivity varies by HIV/ART status 3 6 11.

New and Emerging Tests

• Examples:
  • Molecular nucleic acid amplification (e.g., Xpert MTB/RIF)
  • Host blood transcriptomic signatures (like RISK6)
  • Aptamer-based antigen detection
  • Computer-aided chest X-ray (CAD4TB)
• Strengths:
  Improved accuracy, potential for rapid, point-of-care use, and some can predict risk of progression or track treatment response.
• Limitations:
  Many are not yet widely available or fully validated for all populations 4 5 7 11.

Choosing the Right Test

Test selection depends on:

• Individual risk factors (e.g., age, immune status)
• Resource availability (cost, lab infrastructure)
• Purpose (screening vs. diagnosis)
• Local TB prevalence 1 7

Tuberculosis Screening Test Results & Follow-Up

Understanding TB screening results and appropriate next steps is critical for effective care and disease prevention.

Table 3: TB Screening Result Pathways

Interpreting Results

• Negative:
  Indicates low likelihood of TB infection, especially if immune system is normal. However, false negatives may occur in immunosuppressed individuals 1 9.
• Positive:
  Suggests TB infection; further testing (chest X-ray, sputum tests) required to distinguish latent from active disease. Positive IGRA is more predictive for progression to active TB than TST 9.
• Indeterminate:
  Most common in immunosuppressed or very young/old patients. Should be repeated and interpreted alongside clinical findings 1 10.

Next Steps After a Positive Test

• For Latent TB (LTBI):
  • Rule out active TB with symptom check, chest X-ray, and additional tests if needed.
  • If active TB is ruled out, consider preventive therapy to reduce risk of progression 1 9.
• For Active TB:
  • Immediate referral for full diagnostic evaluation and initiation of treatment.
  • Isolation may be recommended to prevent transmission until treatment is underway 1.

Special Considerations

• High-Risk Groups:
  • In people living with HIV or other immunosuppressed states, tests may be less reliable; combination of tests and repeated screening may be necessary 3 6 10.
• Pediatric Populations:
  • Similar principles apply, but result interpretation may be more challenging due to immune system variability 10.
• Follow-Up and Public Health:
  • All cases of active TB must be reported to public health authorities for contact tracing and outbreak control 1.
  • Ensuring continuity of preventive therapy is essential, especially in transient populations such as jail inmates 8.

Innovations in Monitoring and Follow-Up

• Transcriptomic and biomarker tests (e.g., RISK6) can help monitor treatment response and predict risk of progression, potentially leading to more personalized care 4.
• Point-of-care and rapid antigen tests may soon allow for screening in decentralized settings and among hard-to-reach populations 5 7.

Conclusion

Tuberculosis screening is a vital tool in the fight against a persistent and deadly disease. The choice of test and interpretation of results depend on individual risk, population characteristics, and available resources. With new technologies on the horizon, the future of TB screening looks promising—offering hope for more accurate, rapid, and accessible tools to curb the spread of this global health threat.

Key Takeaways:

• TB screening aims to detect infection early, reduce transmission, and guide public health interventions 1 2 9.
• Main tests include TST, IGRA, CRP, and emerging molecular/biomarker assays, each with strengths and limitations 1 3 4 5 7 9 10.
• Test results must be interpreted in context, with follow-up diagnostics and possibly preventive therapy for those at risk 1 9 10.
• Innovations are improving accuracy and accessibility, but widespread implementation requires further validation 4 5 7.
• Successful TB control relies not only on effective screening but also on ensuring continuity of care and robust public health reporting 1 8.

Staying informed about TB screening advances enables both individuals and healthcare systems to respond swiftly and effectively—making a tangible difference in the fight against tuberculosis.