More Than Just a Number: Why Time of Day Matters in Blood Sugar Testing

By Susan B. Sloane, BS, RPh, CDE

As people with diabetes know, achieving in-range blood glucose levels can be a bit of a “roller coaster” ride. A person with type 1 whose body doesn’t produce any insulin must rely on insulin injections to keep blood sugar in between the “navigational beacons”, while those with type 2 may require insulin, medication to regulate blood sugar, or careful monitoring of food and activity to keep blood sugar in check. This can be challenging, but with knowledge and patience, is quite achievable. First, it’s important to know your target blood glucose range. These targets are generally given to a patient by their health care team and will often indicate a range of acceptable blood glucose levels. The average blood glucose range that the American Diabetes Association’s Standards of Care recommends aiming for is 80-1301.

Self-monitoring of blood sugar is an essential component of diabetes care.2 Blood glucose should be measured at several points during the day, and the number of readings you need to take to achieve the best diabetes control will be determined by your own health care team. Each reading you get will tell you how well your insulin is working and will help you make important decisions concerning insulin dosing and meal planning.

Understanding Fasting Blood Sugar
Blood glucose levels should generally be at the lowest point first thing in the morning, which is known as a fasting blood glucose. As a rule, morning blood glucose levels are a sign of how well your basal, or background (long-acting) insulin is working. If this number is too high, it may be a result of several factors, such as:
• Dinner was too heavy (Perhaps in carbs or fats)
• Bedtime snack was too large
• Illness
• Hormone fluctuations (Such as puberty or menopause)
• Basal insulin is too low (If you are using insulin. If you are not using insulin, your own body’s basal production may not be adequate.)
• Stress

If you have type 2 diabetes, your body produces some basal insulin in the pancreas. If your fasting blood sugar is going over target for a few days in a row, your health care team may suggest increasing your basal insulin, or possibly adding basal insulin to other medications.

What You Need to Know Before You Eat
Another important time to check blood glucose is before a meal. The pre-meal reading will help you decide how much insulin to take if you use bolus, or rapid acting, insulin at meal-time. The insulin dose before a meal will generally depend on how much food, or specifically, how many carbohydrates, you are going to consume at that meal. This dose is sometimes calculated by an insulin-to-carbohydrate ratio, which is basically how many units of insulin it will take to bring your blood sugar within your target range. One example of how to calculate a starting bolus dose is to divide 500 by your total daily insulin dose. This will give you a starting point of how many carbohydrates are covered by 1 unit of rapid-acting insulin such as insulin aspart, lispro, or glulisine. Different medical practices use this formula as a starting point, but there are other methods, as well.

If your blood glucose is higher than your target before a meal, you may need more insulin than usual to correct for this. If you are not currently using insulin, your health care team may suggest adding basal or bolus insulin or a different medication to get your body to produce more insulin to cover meals. Conversely, if you have a low blood glucose reading before a meal, you will possibly need to eat more or take less insulin for a given meal.

It’s Not Just Carbs…
It’s important to be aware that there are many variables that affect blood sugar beyond just carbohydrate intake. If your pre-meal lunch or dinner blood sugar readings are higher than target, it may be because:

• Your previous meal was too heavy in carbs or simple sugar
• If you use meal-time insulin, your dose may be inadequate
• You had a recent snack, which may have been too much
• Your current medication regime may not be adequate to keep blood sugar in range
• Stress, illness etc.

Exercise during the day, for example, can bring blood sugar down lower than expected for up to 48 hours after exercising.3 Alcohol is another important variable that can cause a drop in blood glucose for several hours after drinking, depending on how much alcohol is consumed.3 It is important to take these components into consideration when making decisions on insulin dosing and food consumption.4

When’s Best to Test?
Testing blood sugar 1 ½ -2 hours after a meal will give you important information as to whether the insulin dose used before the meal was adequate or perhaps too much. It also can indicate how a given meal affects blood sugar whether you use insulin or not. According to the American Diabetes Association, a good post-meal blood sugar target is 180 or below. 2 Your health care provider may give you personalized goals that may be a bit different. Not every patient always has the same target values. We will discuss the reasons for this variation in target values between patients in future installments of these articles.

Post-Meal Readings Are High? This May Be Why:
• Your insulin dose was not enough to cover your meal if you use meal time insulin
• Your meal was too heavy in carbs/sugar
• Your current medication regime may not be adequate to keep blood sugar in range
• Stress, illness etc.

Staying on Track with Dario
The key with analyzing any blood glucose value is to establish a pattern by charting your values. The Dario blood glucose monitoring system can help by automatically recording your readings and giving you a good visual picture of your blood glucose trends. The Dario app is also fully equipped with a “share” feature, to allow you to share your information with healthcare practitioners and any caregivers that will be helping you find solutions to potential roadblocks, and to help cheer you on as you make good progress.

Other Important Times to Test
It is not possible to test blood sugar at every point in time, which is why we pick some key times/instances when blood sugar testing is recommended. It is for example, critical to test blood glucose levels before performing tasks that require long periods of concentration, such as taking an exam or driving a vehicle. Testing blood sugar before exercise is also very important, as exercise causes blood sugar to drop. Using your Dario system, it is possible to record exercise days and even sick days (which cause blood sugar to go up higher than normal) and store all this important information within the cloud for easy access when you need it. Having this information at hand is essential to establishing how your own body reacts to certain conditions, and how best to dose insulin and manage a meal plan.

If your head is spinning, don’t worry. Over time the balancing act becomes second nature. I can say this, having raised two sons with type 1 diabetes myself. And if you need more help, our Hand-in-Hand Coaching Package is now available! Get the one-on-one help you need to find the techniques that work for you, based on your expectations, your goals, and your lifestyle. By working with me, as a CDE, you’ll learn how to read between the numbers and understand more about how foods affect your unique body. Click here to learn more and sign up.

I look forward to meeting you!