Active?

"mongerel" writes

QUOTE

for detecting confirmed active Tuberculosis (TB) disease.

Only just noticed this after re-reading the press release. Is this a miss-print or a giant leap forward or what? 

 He is referring to the following from the Diel Meta Study 

..Interferon Gamma Release Assays (IGRAs) are superior to the previous standard in diagnostics, the 100+-year-old tuberculin skin test (TST), for detecting confirmed active Tuberculosis (TB) disease.

The reason that they use Active TB as the indicator is that there is no Gold Standard for Latent TB. That is, if you were to try to directly determine the efficacy of a new diagnostic (ie QFT-TB Gold In-tube) you would need something to measure it against. Given that there is no way to directly and correctly determine if somebody actually has latent TB* (other than the new test) then there would be no way to determine how accurate the new test is. Consequently, they use confirmed (by other methods) Active TB as a "surrogate" for latent TB.


Bear in mind that QFT-TB Gold In-Tube does not differentiate between Active and Latent TB. So, yes, QFT-TB Gold In-tube can be used to detect Active TB as well as Latent TB.


The only other way to determine if somebody has latent TB after having tested them with QFT-TB In-Tube is to not treat them and wait to see if they progress to active TB. There are obviously some ethical problems in conducting a trial in this way. However, there have been a few trials where this has been done (basically by the patient themselves electing to not have treatment). The results from these trials have also been excellent. The Halder case in the UK is a recent example of this. They found that, within 2 years, 15% of QFT positives, without treatment, progressed to active TB. 


* The fine print. There actually is one other way to determine if a patient has latent TB, In simple terms it requires the killing of the subject and dissection to find the latent TB. Understandably, it is very hard to find volunteer subjects for this type of trial.