Cellestis: Predictive.

I have mentioned before that the predictive value of the QFT diagnostic is extremely important in proving its value.


This longitudinal study by Diel confirms the ability of QFT to identify all of those contacts of a case of active TB that subsequently progress to Active TB.


It is actually quite difficult to conduct a study like this where a large number of people are identified as having TB but are not treated. Therefore these results should be treated like "gold".


In essence, in a group of 903 people exposed to TB, the TST reported a huge number of positives (604 or 229). QFT only reported 198 positives.


The crucial part, however, is that whilst reporting less positives, the QFT did not miss a single case that progressed to Active TB over the subsequent years. The TST missed 2 of the 17 cases that progressed to Active TB.


Rationale: Only limited data are available on the predictive value of Interferon- release assays (IGRAs) for progressionfrom latent tuberculosis infection (LTBI) to active tuberculosis (TB). Objective: To build on our initial study comparing theQuantiFERON®-TB-Gold In-Tube assay (QFT) with the tuberculin skin test (TST) in close contacts of TB cases and evaluating progression to active TB for up to four years. Methods: A cohort of close contacts of smear-positive index cases established between May 2005 and April 2008 was tested with QFT and TST. Through April 2010, progressors to active TB were consecutively recorded. Results: Of the 1,414 contacts (141 children), 1,033 were still resident in Hamburg at the end of the study period, and results of both tests were available for 954. QFT, but not TST results were associated with exposure time (p < 0.0001). For QFT, 198/954 (20.8%) were positive; 63.3% (604) were TST positive at > 5mm and 25.4% at > 10mm. 903 contacts refused chemoprevention and 19 developed active TB. All 19 (100%) had been QFT-positive with a progression rate of 12.9% (19/147) over the observation period. Corresponding values for the TST were significantly lower: 89.5% (17/19) and 3.1% (17/555) at > 5mm, and 52.6% (10/19) and 4.8% (10/207) at > 10mm, respectively. The progression rate of 28.6% (6/21) for QFT-positive children was significantly higher than 10.3% (13/126) for adults (p=0.03). Conclusions: Results suggest that QFT is more reliable than the TST for identifying those who will soon progress to active TB, especially in children.


(finally, I beat Rog on one)