Why Test Strips Are Coded

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So That's Why Test Strips Are Coded! (And Other Diabetes Questions Answered)

I’ve had diabetes for (mumbled…) years. That’s right, I’m (mumbled…) years old and I’ve had diabetes for (mumbled…) years! That’s a long time! And still, there are things about diabetes that I’ve just never really stopped to question. They mostly fall into the category of “information that might be interesting but won’t change how I manage things.” There’s a fair amount of information that can fall into that category. The latest example of this kind of thing was highlighted by a question my wife asked me.

“Why is there a code number on your test strip bottle?” she asked me. And I had no idea. The best I could say was, “Well, there’s always been a code, and I know it’s important to make sure the code on my meter matches the code on the strips, because… You know, coding… Or something.” The answer to that question won’t change what I do with the information my meter is giving me, or affect how I live my life in any way, but it got me curious, so I went sleuthing.


It turns out, test strips are coded because the enzymes used in them to gauge blood glucose can vary greatly from batch to batch. The coding system is a way to calibrate the meter to the particular strength of enzyme in a given batch — the meter is programmed to expect a certain strength depending on the code it is given. But then I started thinking about this a little more — I’ve had the same code (25) on every single vial of my test strips for the last three years!! Every single box — code 25. What gives? Turns out, it has become much easier and more common to limit the variability in the enzymes in test strips, and so most companies have only a few codes that are actively used anymore, which is why every box of my test strips for the past three years has had the same code.

Having discovered the answer to my first line of inquiry, I decided to keep digging! Certainly there were other terms, practices, and conventions that I had never really bothered to consider in detail. I thought about it for a little while, and then realized that the holy grail of diabetes management feedback, the (drumroll please…) HbA1c reading, was another number that I really didn’t fully understand. I knew my target, I knew what the numbers meant in terms of potential future health issues and how the numbers reflected on my overall control, but I wasn’t exactly sure what an “HbA1c” even WAS!

So, back to the Internet I went! And here’s what I found: Hemoglobin is a protein inside our red blood cells. The red blood cells’ primary job is to carry oxygen throughout our bodies and carbon dioxide back to the lungs. These cells tend to have about a 120-day lifespan, and during that time, glucose will attach itself to the hemoglobin in them. If there is a high level of glucose in the blood, the hemoglobin will accumulate more glucose. If the level is lower, it will accumulate less. Over the course of the roughly 120 days, all of that glucose STAYS with the hemoglobin in the cells, leaving you with an accumulated total that can be measured and averaged out to give us an “HbA1c reading.” Now, it doesn’t tell us anything about any particular day or week or anything like that — it’s really just giving us a “total accumulation” for the lifespan of the red blood cells we’re measuring, and then we’re dividing that accumulation by the lifespan of the cell to arrive at what kind of “average” blood glucose that might be.

But… HbA1c readings aren’t perfect. If you have many, many low blood sugars on a regular basis, you might have a “false low” HbA1c reading. That is, your extreme lows will be leading to many periods during which you accumulate very LITTLE glucose in your hemoglobin cells, and this might offset periods of HIGH blood sugar where glucose is rapidly accumulating. The end result could be an HbA1c that looks like a solid “middle of the road,” on-target number, but in truth is a reflection of simply averaging a lot of severe lows and a lot of severe highs to arrive at that false middle! And that’s some good information to know right there!

There’s more to know!
There’s a lot more information out there to be uncovered — I might keep digging and share some more of it next week. What exactly do our meters read to determine our blood sugar? Why can’t I mix Lantus and fast-acting insulin in the vial before I inject them — they’re both going into the same place, aren’t they? And for that matter, how in the world have scientists been able to make insulin so variable in its timetable within the body? Stay tuned to find out next week!

The FDA has approved an extended-release metformin combination medicine for adults with Type 2 diabetes. Bookmark and tune in tomorrow to learn more.

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