How low-cost is low-cost?

Ok, there are times when marketing hype becomes flat out ridiculous. Last month, Cepheid announced a new low-cost PCR based test for Tuberculosis. Several challenges with performing PCR on mycobacteria aside (its actually extremely difficult to get DNA out of the buggers) this would be a great breakthrough. PCR has the potential to be an extremely specific, extremely sensitive diagnostic test for… well, pretty much any infectious disease. Its not without its problems, however.  I had a chance to hear Dr. Jason Stout (director for TB control in NC) talk about some of the issues they’ve been having with their PCR. These problems have been enough of a showstopper than they still rely primarily on liquid culture which beats their PCR solution in sensitivity, specificity and cost.

Still, a low-cost PCR test would be a big deal, the problem is that Cepheid’s test is most definitely not a low-cost test. In fact, the cheapest PCR readers that Cepheid sells will cost you about $27,000 a unit. You could buy a flow cytometer for that much and you’d save a lot more lives using that kind of cash by doing CD4 counts than TB diagnostics when there are simpler, cheaper solutions for TB already out there.

Interestingly enough, this was developed in collaboration with FIND, a Gates-funded non-profit working on diagnostic technologies for developing countries. This really casts a lot of doubt in my mind about FIND’s priorities when it comes to developing world diagnostics. FIND’s product pipeline for TB diagnostics limits itself to three approaches: squeezing incremental improvements out of microscopy, making better and cheaper PCR/NAAT based tests and developing antibody-based rapid tests.

I think there’s a huge gap between the first category and the second two in terms of their “appropriateness” for the countries they’re trying to help. Microscopy is dirt cheap, its a relatively poor diagnostic test but it scales very easily. Incremental improvements will help, but really, as a diagnostic test its in bad need of an overhaul. PCR/NAATs and antibody tests suffer from a lot of draw-backs, mostly centered around their costly, proprietary, short-lived and temperature sensitive reagents (I shudder to think of how long PCR probes would last at 40C).

As second-line tests, these approaches may bear significant fruit, but the lack of effort in developing the $1 screening test that’s badly needed to replace the aging microscope is extremely troubling. Without an easy-to-use, scalable and cost-effective first-line diagnostic, we will never be able to bring the TB epidemic under control. No amount of amazing species differentiating, drug-resistance detecting, super sensitive diagnostic tests will be able to make a significant, sustainable impact in these markets if their prices can’t drop an order of magnitude or more over the next few years.