Blood Sugar Monitoring

What Do the Numbers Tell You?

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Blood Sugar Monitoring: When to Check and Why

“I must admit that I stopped checking my blood sugar,” Dave said. “I used to stick myself and write the numbers in a book, but I had no idea what they meant. I’d eat the same thing and get different numbers. Finally, I just gave up.”

Sound familiar? Many people dutifully check their blood glucose levels but have no idea what the numbers mean. Part of the problem is that blood glucose levels constantly fluctuate and are influenced by many factors. The other part of the problem is that no two people are alike. A blood glucose reading of 158 mg/dl in two different people might have two different explanations.

Most people know that their bodies need glucose to fuel their activities and that certain foods or large quantities of almost any food will raise blood glucose. That’s the easy part. But just as cars require a complicated system of fuel pumps, ignition timing, batteries, pistons, and a zillion other things to convert gasoline into motion, our bodies rely on an intricate system to convert glucose into energy.

Learn More About Blood Glucose Management >>

Back to basics

Insulin is a hormone secreted by the pancreas that helps regulate the way the body uses glucose. Its main job is to allow glucose in the blood to enter cells of the body where it can be used for energy. In people who don’t have diabetes, the pancreas changes how much insulin it releases depending on blood glucose levels. Eating a chocolate bar? The pancreas releases more insulin. Sleeping? The pancreas releases less insulin until the wee hours of the morning when the hormones secreted in the early morning naturally increase insulin resistance, so the pancreas needs to release a little more.

Insulin also controls how much glucose is produced and released from the liver. Glucose is stored in the liver in a form called glycogen. When blood glucose levels drop, the liver turns glycogen into glucose and sends glucose to the bloodstream. When there is enough glucose in the bloodstream, the pancreas signals the liver to stop sending glucose into the bloodstream. This system of signals and feedback loops keeps the delicate coordination of insulin release and blood glucose in balance.

In Type 1 diabetes, the coordination of insulin release and blood glucose is completely out of balance because the pancreas stops making insulin. Injected insulin is used to replace what is missing and supply insulin’s signals again.

With Type 2 diabetes, the pancreas makes insulin but not enough to keep up with the body’s demand. Studies have shown that Type 2 diabetes is progressive, meaning that the beta cells of the pancreas make less insulin over time. In addition, the cells of the body are unable to take glucose out of the bloodstream when needed because they resist the insulin that you need to allow glucose to enter cells. On top of that, the liver continues to send a lot of glucose into the bloodstream even when it isn’t needed because the signals telling the liver to shut off aren’t working. So there are three problems facing those with Type 2 diabetes: not enough insulin, insulin resistance, and a liver that won’t stop releasing glucose into the bloodstream.

What’s normal?

Before any blood glucose reading has meaning, you need to know what you’re aiming for. Target goals for blood glucose set by the American Diabetes Association (ADA) are 80–130 mg/dl before a meal and less than 180 mg/dl two hours after the start of a meal. The American Association of Clinical Endocrinologists (AACE) has defined stricter blood glucose target goals of less than 110 mg/dl before a meal and less than 140 mg/dl two hours after the start of a meal. Ask your health-care provider whether you should use the ADA or the AACE targets as your goal. Both guidelines are based on evidence showing the blood glucose readings that are needed to prevent the complications of diabetes.

The words you use to describe blood glucose monitoring may affect how you feel about it. For example, it might help to call it a blood glucose check, not a test, because the word “test” implies pass or fail. It might also help to refer to blood glucose readings as either in or out of target range rather than “good” or “bad.”

It’s also good to remember that your blood glucose goal is to aim for a target range, not an exact number each time. Before-meal blood glucose readings of 101 mg/dl, 114 mg/dl, 126 mg/dl, and 97 mg/dl may look like they are up and down, but they’re all within the target range defined by the ADA.

When you begin to analyze your blood glucose readings, it is helpful to recognize the difference between an isolated reading and a pattern of readings. Say you check your blood glucose before lunch one day, and you get a reading of 246 mg/dl. You know that the reading is out of range, but so what? To make sense of that reading, you would need to know your pattern of blood glucose readings before lunch. If you checked three days in a row before lunch and recorded readings of 118 mg/dl, 110 mg/dl, and 113 mg/dl, you’d see that the reading of 246 mg/dl doesn’t fit your usual pattern before lunch and therefore isn’t noteworthy.

Knowing your pattern gives you a background for comparison. Isolated readings can still be helpful, especially when your blood glucose is low. But an isolated reading is meaningless without knowing the story behind it. And the story includes the factors that affect blood glucose level, including food, medicines, exercise, stress, and infection.

How often should I check?

Most people check their blood glucose level once a day, first thing in the morning. It’s a common time to check because it’s easy: You get up, check your blood glucose, take your medicines, and eat breakfast. Then you’re done with your diabetes for the day and don’t have to think about it anymore.

The problem with this routine is that it only tells you about your blood glucose pattern before breakfast. You don’t learn what is happening after meals or later in the day. To find meaningful patterns at other times of the day, you have to check at other times of day.

One option for finding more patterns is to check your blood glucose four times per day three days per week. Checking before breakfast, two hours after breakfast, before dinner, and two hours after dinner three times per week for a few weeks will help you identify your patterns throughout the day.

Try to make blood glucose monitoring a useful tool by checking your blood glucose at times that serve you. Blood glucose monitoring should help you make a decision, give you feedback about a decision, and help you learn about your usual patterns.

You also need to consider the cost of the test strips. For those who do not take insulin, Medicare pays for one strip per day, so you want to put those strips to good use. Instead of just checking before breakfast every morning, you might decide to check before and after breakfast on Monday, before and after lunch on Wednesday, and before and after dinner on Saturday. If you take insulin, Medicare and most health insurance plans will pay for the number of strips written by your health-care provider on the prescription.

There are many ways to keep track of your blood glucose readings so that you can evaluate the patterns. You can use a logbook in which you write down the readings along with any comments (such as what you had for lunch or how stressed you were feeling). Depending on what meter you use, you may be able to use computer software that displays the contents of your meter memory in graphic forms.

Here are some common patterns and probable explanations that will help you make sense of your numbers:

My blood glucose is always higher in the morning when I get up and is lower during the day.

    • Your liver might be sending a lot of glucose into the bloodstream because the signals telling it to shut off aren’t working. The drug metformin may be prescribed, because its main action is to signal the liver to shut off.


    • Your dinner or bedtime snack choices might be raising your blood glucose the next morning. Try changing your food choices and portions to learn more about their effect on your blood glucose levels.


    • Your body may be unable to handle the effect of the hormones secreted at dawn that work against insulin. This early-morning release of hormones is called the dawn phenomenon. High blood glucose that results from it can be managed with oral medicines or insulin.


  • Your insulin or oral medicine dose may need to be adjusted.

My blood glucose is high all day.

    • If you have Type 2 diabetes, your cells may be resisting your insulin. Exercise, weight loss, and certain medicines will help to make your body more sensitive to insulin and lower your blood glucose.


    • If you have Type 2 diabetes, your pancreas may not be making enough insulin to meet your needs, and you may require oral medicines or insulin.


  • If you have Type 1 diabetes, you may need an increase in your basal insulin doses. Basal insulin is the amount of insulin your body needs in the background all day long. Insulin glargine (brand name Lantus), insulin detemir (Levemir), or NPH can provide basal insulin. An insulin pump is also programmed to deliver basal insulin.

My blood glucose is within range before I eat but high two hours later.

  • It is helpful to understand how the secretion of insulin changes in Type 2 diabetes. The pancreas secretes insulin in response to a meal in two phases. In the first 10 minutes after glucose enters the bloodstream, there is an early burst of insulin release called first-phase insulin secretion. This is followed by the second-phase insulin secretion, a sustained release of insulin that lasts for several hours. One of the early changes in Type 2 diabetes is the loss of first-phase insulin secretion following a meal. This means that not enough insulin enters the bloodstream as quickly as it is needed, resulting in high blood glucose after meals.

Certain medicines taken at mealtimes can help. Oral drugs such as nateglinide (Starlix) and repaglinide (Prandin) stimulate the pancreas to release more insulin when blood glucose levels are higher, while acarbose (Precose) and miglitol (Glyset) slow the rate at which certain carbohydrates are absorbed from the small intestine.

The rapid-acting insulin analogs lispro (Humalog), glulisine (Apidra), aspart (NovoLog), and insulin human inhalation powder (Afrezza) also work effectively to lower blood glucose after meals. Regular insulin peaks too slowly to completely lower blood glucose following meals although some people find Regular insulin is the best choice for them.


  • What you eat makes a difference, too. Your blood glucose reading taken two hours after you start to eat should be about 30 mg/dl higher than before you eat. After-meal readings can tell you about the impact of food on your blood glucose levels. If your blood glucose reading was 111 mg/dl before eating two cups of pasta and 322 mg/dl two hours later, you’ve learned that two cups of pasta is too much for you. However, a reading of 157 mg/dl two hours after eating one cup of pasta tells you how much pasta you can eat to keep your after-meal readings within the target range.


Many people are shocked by how high their readings are after meals. Ralph was convinced that his large restaurant meals every night didn’t really raise his blood glucose levels because his fasting readings weren’t elevated. But when he actually checked two hours after dinner and got readings over 400 mg/dl, he decided to make some changes.

My blood glucose is usually no higher than 130 mg/dl, but for the past two days every reading is over 200 mg/dl.

  • A sudden change in your blood glucose pattern is usually due to infection. The stress hormones released when you are sick tend to raise blood glucose levels. Infection is a physical stress, and when stress occurs, the body reacts by secreting more epinephrine, cortisol, and glucagon. These hormones cause extra glucose to be released from the liver to give the body added energy to cope. Most times, your blood glucose levels will rise even before you get symptoms of an infection.

Two heads are better than one

Dave stopped checking his blood glucose levels because the numbers didn’t mean anything, but some people stop checking simply because the numbers upset them. It’s especially hard when you’ve been following all the rules, eating right, exercising, and taking your medicines and the numbers are still high.

Learning what the numbers mean and evaluating the patterns are tools that can help you cope. It’s also helpful to remember that there are blood glucose readings that defy explanation. Sometimes we just don’t know why a reading is out of range. That’s why it is wise to team up with a diabetes educator or your health-care provider who can offer guidance and a fresh perspective. What do the numbers tell you? The answer lies in knowing your targets, patterns, and who to call when you have a question.

Want to learn more about maintaining target blood sugar levels? Read “What Is a Normal Blood Sugar Level?” and “Blood Sugar Monitoring: When to Check and Why” and see our Blood Sugar Chart.

Originally Published July 20, 2006

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