Apropos to today’s newsflash

Diabetes advocate and author Riva Greenberg has been on a “meter accuracy kick” lately — researching the heck out of this controversial topic. Very timely considering I’ve been seeing loads of expensive TV ads for Accu-Chek’s new Nano meter, claiming that it’s “23% more accurate” (!)

Riva recently published a piece at the Huffington Post on why meter accuracy is both less, and more, critical than you might think. Truth is, she tells us, meter accuracy is only one part of a much larger story.

A Guest Post by Riva Greenberg

After being lucky enough to receive an iBGStar meter from Sanofi the day before its launch, I ran a few comparison tests between it , which I’d been using the past two years, and discovered that the iBGStar consistently gave me a reading 20-25 points higher.

So I took out all my meters. There were several, (Sanofi studies show most people use 4 meters on average) and I even ordered two new free meters from FreeStyle. I checked my blood sugar several times on my collection of 7 meters (some think I was a little obsessed) and saw it was rare when two meters gave me the same number!

Given that I feel like my meter is my lifeline, I wanted to find out how meters work and why different meters give different results.

I talked with a number of Chief Medical Officers, MDs and Medical Safety Officers at several meter manufacturers and I’m going to tell you what I learned in layman’s terms.

To better understand the science behind meter and strip technology, you can google “meter accuracy” for white papers and posts that would delight even the geekiest engineer. To better know how accurate your own meter is (in percentage terms), you can “check the package insert that comes with the strips and look online at prescribing information,” says Shawna Gvazdauskas, Head of Devices at Sanofi Diabetes U.S.

Home vs. Hospital Testing

Most home meters measure glucose in so-called “whole blood” (blood as it comes out of our body). Whole blood consists of a liquid, called plasma, and cells, mainly red cells. The percentage of red cells is called the hematocrit. The standard reference lab test measures glucose in plasma (about half to two thirds of the volume of blood).

Home meters are calibrated to give results as though they are measuring glucose in plasma only (called “plasma-equivalent” results). That said, to some degree we’re already on two different playing fields. Second, laboratory tests eliminate virtually all variation, except for manufacturing variation, from their testing.

What that means, according to Dr. Alan Cariski, Worldwide Medical Affairs & Medical Safety Officer at LifeScan, is that hospital standards are much more exacting than testing at home because in hospitals you have: trained technicians, a controlled environment for temperature and humidity, constant maintenance of the machine that performs the test, with checking and refining of the machine’s calibration several times a day, and a much larger sample of blood (5 ml) that’s analyzed for 60 seconds or more, and at much greater expense.

Cariski says lab tests generally come within about plus/minus 4% of a perfect reading. Andreas Stuhr, Medical Director North America at Roche Diagnostics, more or less confirmed that but added: “Even the lab standard is off 5-7% at times, so plus/minus 20% of the hospital lab test (current ISO standard) isn’t as big a leap as we think.”

So Many Variables

There are many factors that go into producing a blood glucose reading at home, and so there’s a lot of room for variability in the final result.

Some factors have to do with the meter, some with the strip and some, with us PWDs.

In fact, the biggest contributor to inaccuracy is the strips. Here’s the process as simply as I can put it: glucose interacts with an enzyme on the strip, releasing electrons. Another agent on the strip, called the “mediator,” turns these electrons into an electrical current. The greater the glucose concentration, the greater the current. That current then speeds through the strip. Finally, an algorithm (formula) in the meter converts the current into a concentration of glucose. And voila! You get a number.

But there’s a long list of factors that affect meter/strip accuracy:

  • Meter calibration, coding, enzymes and mathematical algorithms (all different in different meters)
  • Variable enzymes in strips
  • Mediator oxidation and strip freshness/age
  • Strips differ somewhat, lot to lot, with somewhat different precision ranges for each lot
  • Strips differ in well size (the space in a strip that holds the blood)
  • Interfering substances in one’s blood from medications (something as simple as Tylenol), and every manufacturer’s nightmare, hematocrit — that percentage of red blood cells in blood, which can interfere with the electrical current
  • Environmental conditions: temperature, climate, altitude
  • Lack of meter maintenance
  • User error — forgetting to code the meter or coding it incorrectly; not washing hands before testing (there may be some sugar residue on your fingers or sweat on hands); leaving strips exposed to air too long; or using expired strips

As for testing twice on the same meter a minute apart and getting a different number (yes, I tried that too!), I learned that the first drop of blood you squeeze out of your finger is not the same as the very next drop of blood. It may contain more interstitial fluid (the solution that surrounds our cells), which can give a lower reading.

What’s Realistic

Dr. Cariski says the best we can probably expect a meter to ever produce is plus/minus 8% accuracy, and we may never reach that due to all the variables listed above. Also, if we want portable meters that require no calibration or coding, use very small blood samples, with less than 10 second read-outs, the next standard the FDA is currently considering (within plus/minus 15% of a hospital lab test) will bring us close to the theoretical limits of what’s possible regarding accuracy. Unfortunately, the technology needed to get meters closer to a lovely plus/minus 5% just doesn’t exist  for now.

As mentioned, the FDA is currently evaluating tighter ISO standards, down to plus/minus 15% for glucose concentrations equal to or greater than 100 mg/dL, and plus/minus 15 mg/dL for glucose concentrations less than 100 mg/dL. The ruling is expected late this year or early 2013.

So the bar is being raised (or lowered in this care), and the vendors are racing to meet it. Some have already hit the plus/minus 15% accuracy threshold, with products like OneTouch’s Verio IQ, the new Nano from Roche and the Contour EZ from Bayer.

Will they have gone far enough? Dr. Barry Ginsberg, topic expert and President of Diabetes Technology Consultants, says for people with Type 2 diabetes who don’t use blood-lowering medications, and check their blood sugar only occasionally to see how they’re doing, our current meter accuracy is fine. For Type 2s on blood-glucose lowering meds, the new proposed guideline of within 15% is appropriate. And for Type 1s on insulin, plus/minus 10% is the goal to aim for; it’s the point at which only 1% of hypoglycemic events would be missed.

I’ve been told by several people in the industry that Agamatrix’s meter and strips are closer to within 10% of a standard lab test. Indeed, Sanofi said they chose Agamatrix as the developers of their new iBGStar because of the company’s WaveSense technology, which is believed to be more accurate with hematocrits (remember, the volume percentage of red blood cells in blood). If you’re adamant about accuracy, you’ll want to look at the meters Agamatrix sells directly: the Keynote, Presto and Jazz meters.

I know for sure I’m not the only one obsessing about this. Fellow diabetes blogger Bernard Farrell told me he had a similar “awakening” about meters showing different glucose numbers when he saw his CGM and meter weren’t tracking. Switching to an Agamatrix meter himself, he saw that it more closely reflected his CGM results, and he was able to bring his A1C down half a percent. There’s at least some anecdotal proof that more accurate meters = improved patient outcomes.

{Disclaimer: I was not compensated by anyone or any company for writing this.}

Thanks Riva, great info! We can’t wait to hear what hot D-topic you’ll be obsessing over next.