Analyze This!

Interpreting Your Blood Sugar Monitoring Log

Text Size:
Interpreting Your Blood Sugar Monitoring Log

Picture this: You’re sitting in an exam room at your doctor’s office. The nurse pokes her head in and says, “Sorry for the wait. He’ll be right with you.” Yeah, you’ve heard that before. To kill some time, you start building a miniature fort out of tongue depressors on the examination table. Add some gauze for fences and an odd instrument for a flagpole, and you have quite a little scene going.

Suddenly, the door swings open, creating a gush of air that flattens your fort. In rushes your doctor, sporting a freshly pressed white lab coat and a chart with someone else’s name on it.

“Miss Baxter, how are we today?”

Now, you sure as heck don’t know who “Baxter” is, but after waiting this long, you’re not about to let him get away.

“OK, I guess. Want to see my logbook?”

You hand him your blood glucose logbook, in which you have scribbled down several dozen readings since your last visit.

“I’ll check that in a minute,” he says. For the next five minutes, he takes you through a virtual medical whirlwind: asking the routine questions; checking your eyes, ears, heart, and feet; reviewing the status of your lab work (the nurse caught the chart error and thankfully brought him the correct one); and asking if you need prescriptions for any of your diabetes supplies. Then he opens up your logbook to a random page, thinks for a moment, and offers the kind of insight that can only come from years of schooling, clinical practice, and intense study in the diabetes field:

“Looks like you’ve had some ups and downs. Are you following your meal plan?”

If you’ve heard this sort of off-the-shelf observation before, you’re not alone. Today’s physicians are charged with so many responsibilities and have so little time to spend with patients that diabetes care rarely receives the attention it deserves. If a physician is lucky enough to offer a team of diabetes educators (or can practice medicine without the pressures of managed care), you might get some help with the day-to-day control of your diabetes. Otherwise, you had better prepare for some serious self-management.

Micromanagement 101

Learning how to interpret your own self-monitoring records can get you closer to the control you’ve always wanted.

Let’s picture that visit to the doctor once again, except this time, you were prepared. When it came time to discuss your blood glucose control, you presented a chart indicating a trend of high blood glucose readings on the weekends and low readings the mornings after exercise. You ask your doctor if it would be OK to reduce your overnight insulin by a couple of units after exercise and reduce your carbohydrate intake by 15 grams per meal on the weekends. Your doctor agrees with these suggestions and adds that the high fat content of your restaurant meals on weekends may have a carryover effect to the next day.

Sounds a bit more productive than “follow your meal plan,” doesn’t it?

Becoming a recording artist

Any good record-keeping system begins with blood glucose readings. If you take more than one injection of insulin daily or use an insulin pump, you should be checking your blood glucose level at least four times daily: upon waking, before your midday meal, before dinner, and before your bedtime or evening snack. Even if you don’t take insulin at each of these times, the blood glucose information is needed to determine when your level might be rising or falling. For example, if your blood glucose is high at dinner, you need the lunch reading to find out if the rise took place in the morning or the afternoon.

For those who take insulin once daily, use oral diabetes medicines, or control their diabetes with diet and exercise, blood glucose readings should be taken twice daily, at least while control is being fine-tuned. Ideally, the readings should be taken at two meals in a row and “rotated” from day to day. For example, on day one, check before breakfast and before lunch. On day two, before lunch and before dinner. On day three, before dinner and at bedtime. Then repeat the process from day one. This approach lets you see when your blood glucose level may be rising or falling.

Blood glucose readings by themselves are not of much use unless they are all running high or low, and for most people, that just isn’t the case. Most people have a mix of highs, lows, and normal readings, and the goal is to figure out what’s causing the highs and lows. So in addition to checking and recording blood glucose levels, it is important to record the amount of insulin or medicine taken and the time it was taken, the grams of carbohydrate consumed at each meal and snack, the type and length of exercise and other physical activities (such as housework, yardwork, shopping, and extended walking), as well as stresses that tend to affect blood glucose level such as illnesses, menstrual cycles, emotional events, and episodes of hypoglycemia.

For those who check their blood glucose twice a day, try to record the pertinent information between the two checks. For example, if you monitor your blood glucose before breakfast and lunch, record all carbohydrates, activities, insulin, and medicines taken from the time you wake up until just before lunch.

To get the most from your record-keeping, organize the information so that it is easy to analyze. A simple daily chart like the one here might serve as a good system. It is often helpful to line up several charts like these in a column so that a pattern of high or low blood glucose at a particular time of day can be detected.

Try it yourself

Whatever type of program you use to control your diabetes, you will benefit from keeping detailed, organized records. Don’t think of it as something you have to do forever; that might seem overwhelming. Try it for a couple of weeks, and then take a few quiet moments to play the role of the impartial physician. Look for patterns and trends. Is your blood glucose level consistently high or low at certain times of day? Do your records give any clues about why?

Nobody expects your blood glucose control to be perfect. But it is reasonable to expect good control most of the time. Every time you make a sensible adjustment, you get one step closer to good control.

So the next time you have an appointment with your doctor, show up armed with useful information and your own personal insight. Who knows? You might both learn something new!

How it works

Let’s have a look at how some people with different diabetes treatment regimens have used tables to find patterns. Examine the three excerpts to see if you can determine the causes of the fluctuations in their blood glucose levels.

Connie. The example here was provided by Connie, a 51-year-old woman with Type 2 diabetes who uses diet, exercise, and oral medicine to control her diabetes. Do you notice anything unusual about her blood glucose levels? What could possibly be done to get them closer to normal? Here are some observations based on her records:

    • Connie’s blood glucose level tends to rise overnight, from bedtime one day to breakfast the next day. She may need to take more medicine at night or eat a smaller bedtime snack.


    • Note that her blood glucose tends to drop between lunch and dinner when she is active. Perhaps she needs less medicine on active days or more carbohydrate at lunch.


  • Walking tends to lower her blood glucose level. Without activity, her blood glucose rose after dinner. But with activity it dropped a bit. Perhaps a daily walk after dinner should be part of her routine.

Daniel. A 20-year-old college junior, Daniel takes multiple injections of insulin. He provided the table here. Can you pinpoint the reasons for Daniel’s erratic control? Here are some observations:

    • Skipping his morning snack made Daniel’s blood sugar lower by lunchtime, so he shouldn’t forget to eat it. With morning runs, he may need a larger morning snack or less fast-acting insulin.


    • Daniel’s blood glucose level tends to rise from lunch to dinner. Perhaps he needs a larger dose of NPH in the morning or fewer grams of carbohydrate in the afternoon. Exams may cause his blood glucose to rise even higher, so perhaps he needs extra insulin on test days.


    • Without any activity after dinner, Daniel’s blood glucose tends to be high at bedtime. He might need extra lispro (brand name Humalog) at dinner if no activity is planned.


  • Following evening basketball, Daniel’s blood glucose level tends to drop overnight. Perhaps he needs a larger bedtime snack or less NPH insulin after playing basketball.

Renee. Renee, a 9-year-old girl, uses an insulin pump. Renee takes a unit of insulin for every 15 grams of carbohydrate plus a “sliding scale” to correct highs and lows at mealtimes. Insulin sliding scales are prescribed increases or decreases made to your mealtime insulin dose based on your premeal blood glucose level. Your health-care provider may advise you to take a larger insulin dose if your blood glucose is above a certain level or a smaller dose if it is below a certain level. While using a sliding scale may be appropriate in some instances, it is not a substitute for good control. So if you are adjusting your insulin doses more than twice a day, you may need to examine your diabetes logbook to find the source of your erratic blood glucose levels or consider the possibility that changes are needed in your overall insulin regimen.

What could account for Renee’s dramatic blood glucose changes, especially during the night?

    • Renee’s blood glucose level is rising during the night, even when she has no bedtime snack. Her basal insulin rate probably needs to be increased from bedtime until morning. (“Basal” insulin is delivered every few minutes in small increments to cover the body’s general need for insulin.)


    • Renee’s high readings at lunch-time are probably due to taking too little insulin at breakfast. She may need a unit of insulin for every 10 grams of carbohydrate at breakfast, plus supplemental insulin to cover any high readings. On gym days, she may only need 1 unit for every 15 grams of carbohydrate.


    • “Grazing” in the afternoon tends to produce high dinner readings even if the snacks are covered with a bolus of insulin. Perhaps Renee should limit herself to one snack right after school.


  • Note that swimming practice and swimming in a meet have very different effects on Renee’s blood glucose. She might need to reduce her dinner insulin to 1 unit per 25 grams of carbohydrate before practice but increase the dose to 1 unit per 10 or 12 grams before meets.

Want to start keeping track of your own blood glucose patterns? Download our free printable blood glucose log book sheets today! (Scroll to the bottom of this page after submitting your information for the link to your download.)

  • Hidden
    MM slash DD slash YYYY

Originally Published July 2, 2010

Get Diabetes-Friendly Recipes In Your Inbox

Sign up for Free

Stay Up To Date On News & Advice For Diabetes

Sign up for Free

Get On Track With Daily Lifestyle Tips

Sign up for Free

Save Your Favorites

Save This Article