Sensitivity and Specificity of QFT:

What is the specificity and sensitivity of QuantiFERON-TB Gold In-Tube?

The specificity of Quantiferon-TB Gold In-Tube has consistently shown to be > 99% in low risk individuals (QFT In-Tube Package insert). Specificity is the probability that the test indicates a person does not have the disease when that person is disease free
The sensitivity of Quantiferon-TB Gold In-Tube is as high as 92% in individuals with active disease, but varies depending on the setting and extent of TB disease. Sensitivity is the probability that the test indicates a person has the disease when in fact that person does have the disease.

Advantages of QFT over Tuberculin Test (TST)

• Antigens IESAT-6, CFP-10 and TB 7.71 used are highly specific and are absent from all BCG strains and most non tuberclosis mycobacteria with exception of M. kansaii, M. szulgai and M.marinum
• Requires a single patient visit
• Not affected by prior BCG vaccination
• QFT is not subject to boosting
• Not subjected to reader bias as may occur with TST

The TST has traditionally been used to screen populations for LTBI, however there is no gold standard for diagnosing LTBI. All screening tests are designed to identify the possibility that a disease might be present and to prompt further evaluation in those who screen positive. For LTBI the only gold standard is the later development of active TB. OFT has been shown to be 6 times better than TST in detecting the individuals who will progress to active TB disease, and this combined with its > 99% specificity provides confidence that OFT is detecting those truly infected.

Advantages of QFT over Tuberculin Test (TST)

• Antigens IESAT-6, CFP-10 and TB 7.71 used are highly specific and are absent from all BCG strains and most non tuberclosis mycobacteria with exception of M. kansaii, M. szulgai and M.marinum
• Requires a single patient visit
• Not affected by prior BCG vaccination
• QFT is not subject to boosting
• Not subjected to reader bias as may occur with TST