When to Check Blood Sugar

“I don’t get this diabetes thing,” Zach, a 50-year-old friend with Type 2, told me. “I check my sugars twice a day, and they’re always below 110. But my A1C is 8.4%. My doctor says that’s way too high. What’s going on?”

Zach’s problem is easy to explain. He’s testing at the wrong time. Every day he checks on waking and before dinner, when he hasn’t eaten for four hours or so. His numbers are always good because he doesn’t have a problem with fasting sugars.

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If he checked after eating, he would find out where his high A1C level comes from. He probably runs high numbers for several hours after meals. Those highs are probably doing a lot of damage to Zach’s blood vessels.

Zach is hardly alone. Many people check (or “self-monitor”) at the same times every day. They’re not trying to learn anything new, just keeping a record for their doctor. This mindless testing is a waste of time, as I wrote about here.

So when should you check? Some things to consider:

• The best times to check blood sugar may depend on your medications. If you’re on insulin or an oral drug that stimulates insulin such as a sulfonylurea or meglitinide (or a combination drug containing one of these medicines), you have to worry about both highs and lows. You have to check more often. If you’re not on those drugs, you’re mainly interested in what causes high blood sugar levels and how to prevent them.

• You should check to answer questions for yourself. What foods raise your sugar (and by how much), and which ones don’t? How does your body respond to exercise? What time is best to take your evening metformin to get a good fasting level? How much does bitter melon lower your sugar?

• Diabetes expert Wil Dubois wrote here that no single blood sugar value tells you much. He says you need to test before and after something to learn how that something (food, exercise, medicine, sleep, or stress) affects you. This is called “testing in pairs.”

Test before and after a meal, and you’ll know how that meal affected your sugar. Before and after exercise (and two hours after exercise) and you’ll see how your workout affects you.

Blood sugar checks are best thought of as experiments. If you want to find out if vinegar at bedtime lowers your morning sugar, try two nights with it and two nights without it to compare. You can research almost anything about your diabetes by checking at different times and keeping records.

• The records are important because you’ll never remember several numbers, nor will you remember what you ate or other things that might affect your glucose results.

• Shift work and high-stress jobs tend to make glucose levels more variable and so call for more checking.

• Insurance companies often don’t pay for enough strips, especially for people with Type 2. You may have to save up strips by not testing every day. If you can only afford one strip a day, skip a day so you can do a pair of tests on the other day and actually learn something.

Dubois also discusses “burst testing,” which “involves saving up your strips for a month before deploying them in a brief but intense burst of monitoring, and then using this sample of days to project what’s happening during the rest of the month. Bursts are commonly done for three days.”

“If you decide to try burst testing,” Dubois says, “be sure to choose a span of days that includes one weekend day,” since weekends tend to have different patterns of exercise and food.

• You may be able to use cheaper brand meters and strips such as Walmart’s ReliOn brand, though they are not always covered by insurance.

• Continuous glucose monitoring (CGM) makes checking sugars far easier and more helpful. A CGM will not only tell you where your sugar is now, but where it’s going. If you’d like to check more often but find practical difficulties in doing so, consider a CGM.

Our blogger Scott Coulter wrote of his new CGM, “I can see if the spike of my insulin is off from the spike that comes with what I eat. I can get a much better sense of WHEN I should inject that short-acting insulin so that spikes match up… [I am] getting much better, more stable, and ‘in-range’ results.”

Readers also had some good tips on testing that worked for them:

Barb, who is on insulin, wrote, “ALWAYS [test] before driving. I wouldn’t feel like I was a responsible driver if I didn’t test before driving.”

Daniel said, “I test before, every half hour during, and after exercise. I tend to suffer lows if I fail to eat right before and sometimes during exercise.”

Liz wrote, “I monitor first thing in the morning when I have tried something new to eat as a snack before going to bed. I find a vast difference in what I should and should not snack on before bedtime.”

Many studies have shown that self-monitoring only improves your outcomes if you use the information. The point of checking is to change your diabetes self-management program to get better results and feel better.

Self-monitoring of blood sugar can be a big help, but only if you do it thoughtfully.

When blood sugar fluctuations come at Scott Coulter with no real pattern, and he can’t understand any GOOD reason for them, he gets seriously annoyed. Bookmark DiabetesSelfManagement.com and tune in tomorrow to read more.

  • Goblin

    You suggest using a different meter for burst testing. My experience is that different meters are not comparable with each other. I had to change meters this year because the test strips for my prior meter were no longer on my Medicare Advantage formulary. During the first six weeks I tested using each meter. I had a reading difference of -9 to 24, -6% to 31% swing. I will most likly pay out of pocket for my prior strips because that meters results were in line with my hA1c. Yes, I know the Fed quide lines allow for a swing of up to 20% between meters.

  • JohnC

    Right on David… Your A1c is great for finding out if you’re on the right track, but even when it’s pretty good it could just be an average of some very high blood sugar readings and some really low ones.
    The only way to find out how well you’re doing is to test before meals, after meals and over night.
    Yes you’ll need lots of test strips but hey if you want to be in good shape when you get old (like me) there really is no other way. Go online and buy test strips for under $25 a hundred.
    And watch the carbs. A nice piece of whole grain bread in your body is equal to 3 teaspoons of sugar.
    Got a chuckle out of the recipe this week – 47 grams of carbs per serving. Really! That’s as much as I consume all day.

  • linda

    I use Walmart’s ReliOn meter and strips for all of my ‘extra’ tests. Prescription strips are too expensive. I’ve found the glucose tests using the ReliOn Prime match the prescription brands within 5 points either way.

  • Ronda

    I was frustrated that my insurance didn’t cover more strips. Finally, I chose the Kroger brand meter and strips. I checked their accuracy against my existing (3 different brands) meters – perfect. NOW I can test 7 times a day, fasting, before and after meals and exercise – the more I can test, the better my numbers. If you go for a store brand meter, simply check it against your more expensive meter to make certain they give almost identical readings – then go ahead and save!