Whose endo regularly suggests you get a GlycoMark test? Wait, better question: who has the slightest idea what constitutes "in range" for the GlycoMark test, or what the heck you're supposed to do with the results?
Yeah, I thought so... me neither.
We've mentioned GlycoMark a few times here at the 'Mine, but when it recently came up in conversation, our team basically all looked at each other and shrugged. This year's ADA Conference seemed like a great chance to get a better understanding. The company (yes, the GlycoMark test is provided by a single North-Carolina-based outfit of the same name) didn't have a booth, but I did have the opportunity to meet up with Scott Foster, president of GlycoMark, and a few others to pick their brains about the history and meaning of this "other" glucose-levels blood test.
Where Did It Come From?
The hemoglobin A1C was introduced as a means for monitoring the "control of glucose metabolism" in the late '70s, and quickly became the gold standard, because it gives us a three-month average of where our BG levels stand. But that's pretty much it for definitive glucose tests, right? And we all know that an average can be deceiving, masking the highs and lows that may be occurring between tests.
The GlycoMark test is based on a molecule called 1,5-AG (short for 1,5-anhydroglucitol), discovered in 1880, and later developed as an assay by a Japanese company. Essentially some researchers noticed that diabetic patients have a decreased amount of this substance in their blood, and even less when their blood sugars are running really high. It first got attention in the U.S. following a 2006 Diabetes Care journal article on a study of its validity in indicating the severity of glucose swings a person has experienced in the past two weeks, Foster tells me.
This test is already used widely in Asia as a key indicator of blood sugar control, and you may be hearing more and more about it here. Note that famous type 1 researcher Dr. Irl Hirsch wrote about it in 2010 and 2011, and reportedly has another paper in the works.
What's a "Good" Result?
According to Kim Stebbings, who just recently left Roche to join GlycoMark, the "Test Goal" for this marker is not a percentage like the A1C. It's a basic number that can be a bit confusing, because unlike the A1C, the higher the number the better!
People with diabetes should aim for a GlycoMark test result greater than 10 micrograms/mL, the experts say:
- A GlycoMark of 10 ug/mL would mean the average daily post-meal blood sugar over the past 1-2 weeks is approximately 185 mg/dL.
- A GlycoMark of 12 ug/mL would mean an average post-meal blood sugar of 180 mg/dL.
- At the low end, a GlycoMark of <2 would mean average daily excursions above 290 mg/dL, so as the GlycoMark goes down, it indicates more extreme high blood sugars.
Why Should You Care?
"You can have two patients with an identical A1C at goal, but one can have significant glycemic variability," Foster says, adding that 40% of patients between 8% and 6.5% A1C (defined as the moderate zone) experience severe glucose swings.
Stebbings elaborates in an email: "If people are not using continuous glucose monitors, and do not do post-meal blood glucose tests, or if they have frequent hypoglycemia, it can be difficult to see these excursions as A1C only measures average blood sugars. People with a 'normal' or near-normal A1C can have extremely diverse GlycoMark tests, so the test is indicated for anyone with an A1C under 8."
GlycoMark is really useful to show if new medications are working, the pair tells us, because it shows variability within a two-week period after a new med is started. It's also helpful for physicians to "separate out patients having problems," Foster says, referring back to the fact that even with a decent A1C, some patients are not faring so well with too many high and low points.
But if you're a type 1 on insulin with a good A1C, and you're not having any knock-out lows, is this test really useful? That was my question.
"The value for the type 1 patient is not great," Foster says, unless they're interested in gauging the effectiveness on post-prandial sugar levels of a new drug like Symlin, for example. I mentioned that GlycoMark results could also be useful for folks trying to get insurance pre-authorization for a CGM system. You know, to show that you need a CGM because you're doing the glucose bounce-a-thon. Foster liked that idea!
Finally, there's some study being done on the value of using GlycoMark + A1C as a dual measure to predict diabetes in people at risk.
Where and How Much?
Lots of mainstream labs now offer the GlycoMark test, including Quest, LabCorp, and Specialty Laboratories.
About 25,000 of these tests are now done in U.S. per month — about 2% of the number of A1C tests, Foster says. But it's getting more popular because it's so affordable. "We can get panels to doctors for not more than $39... so it's a cheap test that can show drug efficacy," he says.
btw, the approximate cost if billed directly to a patient is around $75-$80 (way cheaper than most lab tests!) and if the billing is physician-based, the cost to you is probably about a $20 co-pay.
Because it's so cheap and measures the immediate past two weeks, physicians can use it monthly, Foster says. And he proudly notes that the test is not affected by hemoglobothoglies (certain genetic defects) like the A1C is.
A few warnings to keep in mind, though:
* the test won't work for people with stage 4-5 kidney disease, as that interferes with results
* the "normal" range is defined differently in different locations, for example in Asia, where ingesting soy affects the readings
* watch those result numbers here in the U.S. too, because individual labs often have different "normal" thresholds -- and because (don't forget!) a higher GlycoMark is better than low.
So there you have it: the mysteries of the GlycoMark revealed.