Glucose Monitoring: What's the Point?

A friend of mine who was recently diagnosed with Type 2 diabetes called me the other day. He was sort of embarrassed to ask, but he finally did: “So they sent me home with this meter… but my numbers are just high all the time… what I am supposed to do with these numbers, anyway?”
Wow. How ridiculous! That’s not the first time I’ve heard of doctors sending patients home with a glucose monitor but no explanation of why or how to use the information it provides.
Why is it so important to check your blood glucose (BG) frequently, anyway? Especially when your doctor insists that you have an A1c test every three months, in order to evaluate how your blood glucose is doing?
Very good questions. Now listen carefully, ‘cause I’m gonna explain: While the A1c and your daily BG measurements are obviously related, you need to view them as distinct entities, providing very different types of information.

The A1c test, conducted in a doctor’s office or laboratory, reflects your average BG levels for about the past three months. It looks at the big picture, i.e. “What effect are my BG levels having on my chance of future complications?” But if your A1c turns out to be above your target, this test doesn’t provide a clue as to what you can do about it. A high A1c result only tells you that you need to change something. Your individual daily glucose results, on the other hand, provide information that you can act on right now.

Your Meter as a Compass
Patients taking insulin usually need regular BG readings to make daily adjustments to their insulin doses. But even if you don’t take insulin, you can use your glucose meter to demonstrate the effects of specific foods, meals, and exercise, and to determine whether your BG is too low. Think of your meter as a compass, which tells you where you are right now, so you know which way to head next.

Let’s say you find yourself at a surprisingly high 240 mg/dl at bedtime. Now you can think briefly about whether your evening was different than usual. Did you eat different foods? Or sit very still while watching TV instead of doing dishes and straightening up the kitchen? In any case, you know you need to lower your BG now by taking a walk or climbing some stairs, or other activity. And you may want to try a different dinner choice tomorrow night, to avoid repeating the high.

Perhaps the most important reason to check your BG regularly is that it can tell you if you are hitting your general BG targets, and obtain early warning about changes in your overall BG control (before your A1c goes out of range).

Try using your meter’s memory function to check your average readings for the last 7, 14, and sometimes even 30 days. This offers a great “progress report,” which can actually be very motivating, if for example, you’ve started a new exercise program and want to see whether you’re making a significant impact on your health (by lowering your average 10 points or more).

The best times to check your BG depend on your reasons for checking. If you are checking in order to choose your insulin doses, then the best times to check are before meals and at bedtime. Checking at the same times each day is helpful when your purpose is to assess improvement or change in your overall control.

What About Targets?
You may not be exactly clear on where your BG numbers should be. The standard A1c target is 7.0 or below. The traditional targets for daily testing are less than 130 before meals, and less than 180 after meals. These ideal daily numbers are somewhat misnamed as “targets,” however: they’re really better viewed as “normal” readings that people without diabetes experience almost all the time. So do not stress out if you find you are sometimes at 140 before lunch, or 210 two hours after supper.

Also be aware of a somewhat quirky difference between your A1c and your daily glucose targets: many patients with diabetes can meet their A1c target, while missing their before- and after-meal targets frequently. What does this mean? Remember that the A1c is an average number, in other words a point that reflects the “middle” of all your glucose values in the past three months. So you could have a “perfect” A1c result of 6.5 that might actually reflect the mid-point between several weeks of severe highs and lows. Not good.

If, however, your A1c met your target, and you did not have frequent low BG values, then all of your levels during the previous three months were OK. They were OK even if they occasionally fell out of the target ranges mentioned above. There will always be fluctuations, which is why the A1c is the perfect complement to daily testing.

All Glucose Readings are Good
It’s important to keep in mind that checking your glucose is not the kind of test that you either “pass” or “fail.” In fact, all glucose readings are good! — good in the sense that if you hadn’t checked, you wouldn’t have that information.

For example, you might notice that you tend to get very high readings after breakfast, while your late afternoon levels are not nearly as high. This would give you a tip to consider changing your breakfast menu and/or to schedule your exercise mid-day in order to bring your glucose levels down. Addressing these “problem areas” will of course improve your control over time and bring down your next A1c result.

Patterns of BG changes generally make sense, but single results often don’t. Importantly, diabetes-related complications are never brought on by just one value, but rather over lengthy periods of time, which is reflected by an increased A1c (and high A1c values over years). All of the existing clinical research tells us that your A1c is the vital indicator of your future health. And your glucose meter is a vital indicator of how you’re doing on a daily basis, leading up to your A1c.

Happily, BG monitoring has undergone a quiet revolution. Monitoring didn’t become common until the 1980s. Even in the ‘90s, glucose meters were often inaccurate and cumbersome, requiring larger drops of blood (more “ouch” to the stick) and taking almost a minute to deliver your result. Today’s meters have made self-monitoring much easier, less painful, and much faster. Your personal BG results will supply you with the regular feedback you need to keep your diabetes on track.

Amy Tenderich is creator of the popular web log www.diabetesmine.com and co-author of the new book, “Know Your Numbers, Outlive Your Diabetes”—from which the information in this column is derived.