QuantiFERON-TB Gold (QFT) and Tuberculin Skin Test (TST): Introduction, Differences, and Keynotes

Introduction of QFT) and TST

Interferon-Gamma Release Assays (IGRAs) are a newer blood test for tuberculosis that detects TB infection by measuring the release of interferon-gamma (IFN-g) from patient T cells after stimulation of a whole blood sample with highly specific TB antigens. QuantiFERON-TB Gold (QFT) is a highly sensitive and specific assay than the conventional tuberculin skin test (TST) in which interferon-gamma is tested.

TST is also familiar with the tuberculin tests or tuberculosis skin tests or Mendel–Mantoux test or tuberculin sensitivity tests or purified protein derivative (PPD) tests. It is a tool for screening for tuberculosis. The standard recommended tuberculin test is the Mantoux test and it determines if someone has developed an immune response to the bacterium that causes tuberculosis i.e. M. tuberculosis. PPD used in this test is the extract the components of the organism from TB cultures. This response can occur if someone currently has tuberculosis, if they were exposed to it in the past, or if they received the BCG vaccine against tuberculosis.

Differences between QuantiFERON-TB Gold (QFT) and Tuberculin Skin Test (TST)

The differences between QFT and TST are as follows-

Features	QuantiFERON-TB Gold	Tuberculin Skin Test
Short-form the test	QFT	TST
Nature of the test	Interferon-gamma Release Assays	Tuberculin sensitivity tests
Sensitivity	Low sensitive	Highly sensitive
Specificity	Low (59% of BCG-vaccinated patients)	High (>99%)
False positives	Due to cross-reaction with the BCG vaccine and other environmental mycobacteria	Unaffected by the BCG vaccine and most non-TB mycobacteria, reducing unnecessary antimicrobial treatments
Patient Follow up	Single-visit testing	Double visit testing
Origin of test	Latest	century-old skin test

Keynotes on QFT and TST

• Estimates indicate that one-third of the world’s population has latent tuberculosis (TB), and around 1.3 million people worldwide die of TB each year.
• TST challenges are high program costs from second visits, unnecessary x-rays, and treatment
• QuantiFERON-TB Gold is a simple, cost-effective solution for tuberculosis screening.
• 3 ml of whole blood is required for QFT and it is ELISA based assay.