Tuberculosis Screening and Testing

Tuberculosis (TB) screening is the testing of people without active disease to identify those infected with Mycobacterium tuberculosis, principally to detect latent tuberculosis infection — a contained, asymptomatic state that carries a risk of later reactivation. The two established tests are the tuberculin skin test and interferon-gamma release assays, which measure the immune response to mycobacterial antigens.

Definition

Tuberculosis screening is the use of immune-based tests, and where relevant symptom and imaging assessment, to detect Mycobacterium tuberculosis infection — most often latent infection — in people without diagnosed active disease, as a form of secondary prevention.

Scope

This topic covers the rationale and tools of TB screening: the distinction between latent infection and active disease, the immune-based tests used to detect infection (tuberculin skin test and interferon-gamma release assays), and the role of risk-based targeting. It also notes the separate role of symptom and radiographic screening for active disease. It treats screening as a reference concept and does not specify whom to test or how to treat, which are governed by current guidelines.

Core questions

• What distinguishes latent tuberculosis infection from active tuberculosis disease, and why does the distinction matter for screening?
• How do the tuberculin skin test and interferon-gamma release assays detect infection, and how do they differ?
• Which populations are prioritised for latent tuberculosis screening?
• Why is detecting and treating latent infection important for preventing future active disease and transmission?

Key concepts

• Latent tuberculosis infection (LTBI)
• Active tuberculosis disease
• Tuberculin skin test (Mantoux)
• Interferon-gamma release assay (IGRA)
• Risk-based (targeted) testing
• Reactivation risk
• Symptom and radiographic screening for active disease

Mechanisms

After exposure to Mycobacterium tuberculosis, most people develop a contained, asymptomatic infection — latent tuberculosis infection — that is not transmissible but can reactivate into infectious active disease, especially under immunosuppression. Screening for this state relies on detecting the host cell-mediated immune response to mycobacterial antigens: the tuberculin skin test measures a delayed-type hypersensitivity reaction to injected tuberculin, while interferon-gamma release assays measure interferon-gamma produced by sensitised T cells exposed to M. tuberculosis-specific antigens in vitro, the latter being less affected by prior BCG vaccination. Neither test distinguishes latent from active infection, so a positive screen for infection is followed by clinical and radiographic evaluation to exclude active disease. Screening for active disease itself uses symptom enquiry and chest imaging.

Clinical relevance

TB screening recommendations determine which people — for example those with recent exposure, from higher-incidence settings, or with immunosuppression — are offered testing for latent infection, and understanding the tests' principles supports appraisal of those recommendations. This entry describes the purpose and basis of screening; decisions on whom to test, how to interpret results in context, and how to manage infection are governed by current clinical guidelines and lie outside its scope.

Epidemiology

Tuberculosis remains one of the leading causes of death from a single infectious agent worldwide, and a large reservoir of people carry latent infection that may later reactivate. Because the lifetime reactivation risk is concentrated in identifiable groups, screening is generally targeted at populations at higher risk of recent infection or of progression rather than offered to the whole population; the specific risk groups and recommendations are set out in the cited sources.

History

Tuberculin testing dates to the late nineteenth and early twentieth centuries, with the Mantoux technique becoming the standard skin test for detecting infection, and mass radiographic screening was widely used in twentieth-century TB control. The introduction of interferon-gamma release assays in the early twenty-first century added an in-vitro alternative less confounded by BCG vaccination, and contemporary frameworks emphasise targeted testing of higher-risk groups for latent infection.

Debates

Tuberculin skin test versus interferon-gamma release assays

Both tests detect infection but neither separates latent from active disease, and they can disagree; the relative role of each depends on factors such as prior BCG vaccination, the need for a return visit, and the population being tested, which remains a practical judgement informed by guidelines.

Key figures

• Madhukar Pai
• Dick Menzies

Seminal works

• pai-tb-primer-2016
• menzies-ltbi-2023

Frequently asked questions

What is the difference between latent and active tuberculosis?

Latent tuberculosis infection is a contained, asymptomatic state that is not transmissible but can later reactivate into active, infectious disease; screening tests detect infection, and further evaluation is needed to determine whether disease is active.

Do tuberculin skin tests and interferon-gamma release assays tell you if someone has active TB?

No. Both tests indicate infection with the tuberculosis bacterium but cannot distinguish latent infection from active disease, so a positive result is followed by clinical assessment and chest imaging.