As a physician, you would probably be more interested in positive and negative predictive values, which tell you the likelihood that you positive test will really mean the patient has the disease, and the likelihood a negative test exludes disease. Both are really not great for IGRAs, and those tests are not recommended to confirm or exclude TB disease.

An excellent metaanalysis on patients with positive IGRAs (latent TB) and likelihood of developing TB can be found at http://www.ncbi.nlm.nih.gov/pubmed/21846592

Thanks Dr Norbert

This was the topic of my doctoral dissertation, and I think I may be able to help you a bit.

I compared the QFT-G to Mantoux in my study, which involved pediatric close contacts of active TB cases. My study had almost equal distribution of children in the age groups of 1-5, 5-10, 10-15 Yrs. The study was done in a high-burden setting, and I was able to demonstrate a high specificity (95%), but average sensitivity (72%) for the QFT-G.

You will find literature demonstrating high specificity and sensitivity for the QFT-G, many of these studies have been done abroad, and also in low burden countries.

Just an extension to Robert's answer, in Germany (and in most of Europe) IGRAs are recommended for TB testing, but only as indicative tests. A positive IGRA indicates that the patient may be infected, but a negative test does not rule out the possibility of infection. In exceptional cases (for example, children under 5 with a known TB exposure) treatment is recommended on a positive test, but under normal circumstances, you would not initiate treatment without a full clinical workup indicative of TB, or a confirmed biopsy or sputum sample.

I have no personal experience with Quantiferon blood test. The cited critic opinion based on pertinent literature: "A positive Interferon-Gamma ( γ) Release Assays (IGRA) result may not necessarily indicate TB infection with tuberculous micobacteria. A negative IGRA does not rule out active TB disease".