The key difference between QuantiFERON Gold and T-SPOT is that QuantiFERON Gold detects active tuberculosis infection while T-SPOT detects latent tuberculosis.
The bacterium Mycobacterium tuberculosis is the causative agent of tuberculosis. The immune response to the bacterium is mainly mediated through T-cell activation. QuantiFERON Gold and T-SPOT are two diagnostic tests that detect TB infection through the detection of IFN-γ present in blood samples. These tests are also known as interferon-gamma release assays (IGRAs).
CONTENTS
1. Overview and Key Difference
2. What is QuantiFERON Gold
3. What is T-SPOT
4. Similarities – QuantiFERON Gold and T-SPOT
5. QuantiFERON Gold vs T-SPOT in Tabular Form
6. Summary – QuantiFERON Gold vs T-SPOT
What is QuantiFERON Gold (QuantiFERON-TB Gold (QFT)?
QuantiFERON Gold or QuantiFERON-TB Gold (QFT) is a simple blood test that is carried out to detect active tuberculosis infection caused by Mycobacterium tuberculosis. This test is considered the most accurate test and gives reproducible results for TB infection. QFT is an assay known as interferon-gamma release assay (IGRA) and acts as an alternative to the tuberculin skin test (TST, PPD, or Mantoux). The QFT test is carried out in laboratories and requires only one patient visit, and is also unaffected by the Bacille Calmette-Guerin (BCG) vaccination. This test is highly sensitive and specific, where a positive result predicts a true infection with M. tuberculosis. It is also convenient and performed through Enzyme Linked Immuno Sorbent Assay (ELISA) technology. However, QFT does not have the ability to distinguish between active TB disease and latent TB infection. Therefore, further evaluations are done using risk assessment, radiography, and medical and diagnostic evaluations.
Figure 01: Mycobacterium tuberculosis
QFT test requires three tubes to obtain a clear test result. They are nil tube, TB antigen tube, and mitogen tube. The nil tube is the negative control to adjust the background interferon-gamma (IFN-γ). TB antigen tube detects CD4+ T cell responses to TB antigens. The Mitogen tube has a low response; therefore, it indicates an inability to generate IFN-γ. One of the main advantages of QFT is that it uses whole blood to make T-cell incubation simple and fast. This technology is also designed to screen large sample numbers. This provides standards, controls, and reproducibility of assays, which are needed for clinical diagnosis.
What is T-SPOT?
T-SPOT or T-SPOT TB test is a diagnostic test that detects effector T cells that respond to stimulations by Mycobacterium tuberculosis in order to detect latent tuberculosis. The test has an objective of ELISA and belongs to IGRA. It uses a modified version of the ELISA method to enumerate the bacteria-sensitized T cells by capturing IFN-γ near CD4+ and CD8+ T cells. T-SPOT test counts the number of antimycobacterial effector T cells and leukocytes that produce IFN-γ in a blood sample. This test specifically uses peptides called ESAT6 and CFP10, which are expressed by M. tuberculosis. T-SPOT tests help to identify latent TB since it does not rely on reliable antibody production response or recoverable pathogens. This provides the overall immune response of the host against the bacteria.
The t-SPOT technique is fast, specific, and is less influenced by the BCG vaccinations compared to the tuberculin skin test because both of these tests use different antigens. T-SPOT test consists of a nil control, Panel A (ESAT-6) and Panel B (CFP10) results, and a positive control. The results are usually interpreted by subtracting the spot count from nil control from the spot count in both panels.
What are the Similarities Between QuantiFERON Gold and T-SPOT?
- QuantiFERON Gold and T-SPOT are two diagnostic tests carried out to detect Mycobacterium tuberculosis, which causes TB.
- They are in vitro assays or tests.
- Moreover, QuantiFERON Gold and T-SPOT tests belong to IGRA.
- They are fast and specific.
- Both tests detect CD4+ T cell responses through TB antigen.
- Moreover, they are more specific than the standard tuberculin skin test.
What is the Difference Between QuantiFERON Gold and T-SPOT?
QuantiFERON Gold detects active tuberculosis infection, while T-SPOT detects latent tuberculosis. Thus, this is the key difference between QuantiFERON Gold and T-SPOT. QuantiFERON Gold test measures the IFN-γ concentration via an enzyme-linked immunosorbent assay (ELISA), whereas, T-SPOT test measures the number of IFN-γ-secreting T cells via enzyme-linked immune-spot assay (ELISPOT). Moreover, the assay used in QuantiFERON Gold is ELISA, while the assay used in T-SPOT is ELISPOT.
The below infographic presents the differences between QuantiFERON Gold and T-SPOT in tabular form for side by side comparison.
Summary – QuantiFERON Gold vs T-SPOT
The bacterium Mycobacterium tuberculosis causes tuberculosis. QuantiFERON Gold and T-SPOT are two diagnostic tests that detect TB infections through the detection of IFN-γ present in blood samples. These tests are also known as interferon-gamma release assays (IGRAs). QuantiFERON Gold detects active tuberculosis infection, while T-SPOT detects latent tuberculosis. QuantiFERON Gold test measures the IFN-γ concentration via an enzyme-linked immunosorbent assay (ELISA), whereas T-SPOT test measures the number of IFN-γ secreting T cells via enzyme-linked immune-spot assay (ELISPOT). So, this summarizes the difference between QuantiFERON Gold and T-SPOT.
Reference:
1. “Addressing the Need for an Accurate Tuberculosis Screening.” T-SPOT.TB.
2. “Quantiferon TB Gold.” QuantiFERON US, 27 Apr. 2022.
Image Courtesy:
1. “Mycobacterium tuberculosis collection” By nil elison – tuberculosis (CC BY-SA 4.0) via Commons Wikimedia