attention forrestgump.....pxl?, page-4

pxl and cst ... detailed reply G'day,

PROTEOME SYSTEMS

My apologies for not providing a detailed response to this sooner but I wanted to have my facts confirmed before posting. I have now checked with a professional in the field and can provide the lowdown.

Firstly, the conclusion.

The Proteome Systems test will not compete with Cellestis. It may, in fact, eventually help to increase our market some time down the road.

Now, the details.

The two tests (QFT and PS) are quite different, both in how they work and in their potential uses/markets.

Succinctly, PS can only ever detect active TB wheras QFT can detect both latent and active TB. This is a function of how TB works in the body and the methods of detection used. When TB is at the latent stage it is essentially in a state of equilibrium with the immune response of the body. Or, in other words, the battle between the TB and the bodies immune system is at a stalemate. The immune system stops the TB from spreading and the TB bunkers down in a dormant state (in a lymph node, for example). In this state the TB bacterium is contained and is not present in the blood or other bodily fluids.

QuantiFERON can still detect the presence of the TB because it does not rely on detecting the actual TB itself. Instead it detects the fact that the bodies immune system has been primed to fight the TB. Carrying the battle analogy a little further, QFT does not rely on seeing the enemy to know that the battle is raging, instead it relies on observing the troop trains heading for the front.

PS, on the other hand, detects the actual TB bacterium. However, because when the TB is in it's latent form there is no TB in the blood, it will not detect the latent TB.

When TB moves from the latent stage to the active stage things change. In many (but not all) cases of active TB the patient actually sheds the TB bacterium and it can then be detected in sputum and possibly blood. This is what PS is looking for. Incidentally, even though in this phase the battle is turning against the immune system, the immune system is still primed and QFT will still detect the infection.

The sputum smear test also relies on this shedding of TB into the sputum to detect active TB. This test is most commonly used in developing countries because it is cheap. Unfortunately, it is also very innacurate. In the developed world much better tests are available (NAA or PCR) which are highy specific and have good sensitivity. However, as good as these tests are, they still miss cases of active TB because the TB bacterium is not always detectable in blood or sputum. Furthermore, all of the above applies primarily to pulmonary TB, in cases of non-pulmonary TB a very high percentage of active patients will NOT have TB in their blood.

All this goes to say, in summary, that the PS test is likely going to have at least some of the same problems as the best existing tests for active TB. In the developed world their challenge will be to prove that their test has significant advantages over the existing tests.

In the developing world, however, the test may be usefull as a replacement for the sputum smear test in diagnosing active pulmonary TB. It is unlikely that it will provide much utility in detecting non-pulmonary TB. Of course, as always, cost is a major consideration in the developing world. Hopefully with the backing of FIND, PS will be able to provide this test at an affordable cost.

If the above is true (the PS test meets it's claims in the developing world) then it will be a great boon both to world health but possibly also to CST. If through their test it becomes possible to control active TB in the developing world then the use of QFT to identify latent TB in these setting becomes a reality.

I hope in my roundabout way that I have clarified the situation a little. In conclusion, I can only repeat my earlier comment.

The Proteome Systems test will not compete with Cellestis. It may, in fact, eventually help to increase our market some time down the road.


[cross posted from another place]