Introduction

Tuberculosis (TB) remains one of the most prevalent infectious diseases globally, causing significant morbidity and mortality. Diagnosing TB, particularly latent tuberculosis infection (LTBI), has always been a challenge due to limitations in conventional testing methods. The QuantiFERON-TB Gold test (QFT-G), a modern blood test, offers a more accurate and convenient alternative to the traditional tuberculin skin test (TST). In this article, we’ll explore how the QuantiFERON-TB Gold test works, its procedure, accuracy, and the benefits it brings to TB diagnosis and control efforts.

Definition

The QuantiFERON-TB Gold Test is a blood test used to detect latent or active tuberculosis (TB) infection by measuring the immune system’s response to TB-specific antigens. Unlike the traditional tuberculin skin test, it does not require a second visit for result reading and is not affected by prior Bacille Calmette-Guérin (BCG) vaccination.

What Is the QuantiFERON-TB Gold Test?

The QuantiFERON-TB Gold test is a type of interferon-gamma release assay (IGRA). It is used to detect infection with Mycobacterium tuberculosis, the bacterium responsible for tuberculosis. Unlike the traditional skin test that relies on a physical reaction to an injected substance, QFT-G measures the immune system’s response to TB-specific antigens in a blood sample.

Developed by Qiagen, this test is FDA-approved and recommended by the Centers for Disease Control and Prevention (CDC) for detecting both latent and active TB infections. It has been especially valuable in settings where BCG vaccination or non-tuberculous mycobacteria may interfere with skin test results.

Why Is TB Testing Important?

Tuberculosis can exist in two forms:

• Latent TB Infection (LTBI): The bacteria are present in the body, but the person has no symptoms and is not contagious.
• Active TB Disease: The bacteria multiply, causing symptoms like cough, fever, night sweats, and weight loss. This form is contagious and can be deadly if untreated.

Identifying latent TB is crucial to prevent its progression to active TB, especially in high-risk populations like healthcare workers, people with compromised immunity, and those in close contact with TB patients.

Procedure: How the QuantiFERON-TB Gold Test Works

The QuantiFERON-TB Gold test involves a relatively straightforward procedure that includes blood collection and laboratory analysis. Here’s a step-by-step overview:

1. Blood Collection:

A healthcare provider draws a small amount of blood from a vein, typically from the arm. The blood is collected into special tubes containing TB-specific antigens and control substances.

2. Incubation:

The blood samples are incubated with the antigens. If the person has been infected with TB bacteria, their immune system’s T cells will recognize the antigens and release interferon-gamma (IFN-γ), a cytokine involved in immune responses.

3. Measurement:

The amount of interferon-gamma released is measured using an enzyme-linked immunosorbent assay (ELISA). The levels are compared to controls to determine whether the immune response is consistent with TB infection.

4. Interpretation:

Results are typically accessible in 24 to 48 hours and are described as follows:

• Positive: The immune system responded to the TB antigens, indicating TB infection.
• Negative: No significant immune response, suggesting no TB infection.
• Indeterminate: Results are inconclusive, often due to improper sample handling or an impaired immune response.

Accuracy and Reliability

The QuantiFERON-TB Gold test offers improved specificity and sensitivity compared to the TST.

Specificity:

QFT-G has a specificity of over 97%, significantly reducing false positives due to prior BCG vaccination or exposure to environmental mycobacteria. This makes it particularly useful in countries where BCG is part of routine immunization.

Sensitivity:

The test’s sensitivity ranges from 75% to 90%, depending on the population tested. While it is generally reliable in detecting latent infection, active TB cases can sometimes return false negatives, especially in immunocompromised individuals.

Benefits of QuantiFERON-TB Gold Test

The QFT-G test has several advantages that make it a preferred method in many clinical settings:

No Need for Return Visit:

Unlike the skin test that requires a second visit to read the result, the QFT-G test needs only one visit for blood collection.

Uninfluenced by BCG Vaccination:

Many people vaccinated with BCG show false positives on the skin test. QFT-G avoids this issue by using TB-specific antigens not present in the BCG vaccine.

Objective and Standardized:

The results of the QuantiFERON test are generated in a laboratory, minimizing human error and inter-reader variability associated with TST.

Faster Turnaround:

Results can be available within a day or two, facilitating timely diagnosis and treatment initiation.

Effective for Screening High-Risk Populations:

The test is ideal for screening healthcare workers, immunocompromised individuals (e.g., HIV-positive patients), recent immigrants from high TB-burden countries, and people in congregate settings such as prisons or shelters.

Limitations to Consider

While the QuantiFERON-TB Gold test offers many advantages, it is not without limitations:

• Cost: QFT-G is generally more expensive than the TST, which may limit its use in low-resource settings.
• Sample Handling: Requires precise handling and timely processing of samples, which may be challenging in remote areas.
• Limited Use in Children: Its accuracy in children under 5 years of age is less well established compared to adults.
• Cannot Differentiate Between Active and Latent TB: Like other TB tests, QFT-G can only confirm infection, not whether it is active or latent. Additional diagnostics such as chest X-rays or sputum tests are required for confirmation.

Who Should Get a QuantiFERON-TB Gold Test?

According to CDC and WHO guidelines, QFT-G is recommended for:

• Individuals who have received the BCG vaccine
• Healthcare workers and hospital staff
• People with close contact to someone with TB
• Immunocompromised patients (e.g., HIV/AIDS, organ transplant recipients)
• Individuals starting immunosuppressive therapy (e.g., TNF-alpha inhibitors)
• People from regions with high TB prevalence

Growth Rate of QuantiFERON-TB Gold Test Market

According to Data Bridge Market Research, the size of the global QuantiFERON-TB Gold test market was estimated at USD 679.48 million in 2024 and is projected to grow at a compound annual growth rate (CAGR) of 7.8% to reach USD 1,239.15 million by 2032.

Read More: https://www.databridgemarketresearch.com/reports/global-quantiferon-tb-gold-test-market

Conclusion

The QuantiFERON-TB Gold test represents a significant advancement in TB diagnostics. With high specificity, convenience, and reduced risk of false positives, it serves as a powerful tool for identifying TB infections, especially in high-risk populations and BCG-vaccinated individuals.