Thursday, January 26, 2012

The False Premise Underlying Glycomark

The GlycoMark company is a joint venture which, according to its website, is "dedicated to the discovery and commercialization of novel biomarkers for diabetes."

So far it has marketed exactly one such biomarker, often called the GlycoMark test. It has been on the market for roughly twenty years but I've only known a couple of people who tell me their endos order the test regularly; mine never has. The test sort of interested me when I first heard about; you can test just the time spent high? Well, sort of. The wikipedia article on the GlycoMark test* (and the wikipedia article on the A1c test*) read like an ad for GlycoMark. I will summarize what they say.

According to these articles, there is a substance in the body that is excreted when the body excretes sugar, which is at 180 mg/dl. Therefore, people who spend much time with blood sugar have lower levels of this substance (1,5 AG). Therefore, the Glycomark test can tell you if a person's A1c of, say, 6% is because the person had near constant blood sugars between 110 and 170, or if the person's 6% represents blood sugars bouncing between 60 and 320. A Glycomark score in the normal range means the person has blood sugars below 180 almost all of the time, and progressively lower glycomark scores mean more and more time above below 180.

The Glycomark website hints at the problem with this interpretation of the GlycoMark. First of all, if the glycomark score declines with time spent over the renal threshhold, great. But to say that the renal threshhold is "usually >180 mg/dL" is disingenous. Yes, the renal threshhold is often above 180 (although a renal threshhold of 160, say, would not be unusual). But the renal threshhold can also be above 280. And there's TREMENDOUS variation in renal threshhold, between individuals, and even in the same individual at different times.
A secondary and less problematic issue is that the glycomark depends on something which has a wide normal range to begin with. Two nondiabetics could have significantly different glycomark scores.

And while knowing whether or not your blood sugar has been above your renal threshhold MIGHT be important (there's some evidence that kidney damage happens at that threshhold), you can find that out by testing your urine for sugar. I bought 100 urine sugar test strips last year for $15. One glycomark blood test costs, online, $53. Rough choice? I don't think so.

*As accessed today, Jan 26, 2012.

1 comment:

Scott S said...

It's an interesting position, and it could help some doctors/patients, but as you aptly note, it's not really the perfect biomarker. I find it curious in 20 years, GlycoMark has no other biomarker product for diabetes on the market. Really? Why not? If they do what they claim, one would think they'd have plenty of resources to develop better ones. As I said, the test may be useful in some cases, but at prices like that even when insurers negotiate better rates for themselves, it's still costly and the value is not readily apparent except in a few instances.