What The Blood Glucose Numbers Mean

In order to get a complete picture of your blood glucose throughout the day, it is useful to test at different times. Your doctor will help you set your blood glucose targets. Here is what the numbers can mean.  These examples are based upon the American Diabetes Association guidelines.

Fasting blood glucose before breakfast.  This reading on an empty stomach shows how well you use the long-acting insulin that you take.  The number should be between 90 and 130 mg/dL.  Pre-meal blood glucose before lunch and dinner.  This reading shows the effectiveness of your breakfast and lunch insulin doses. The number should be between 90 and 130.Two hours after eating. Your blood glucose peaks a few hours after you eat. This reading shows if the insulin you took was enough to cover the carbs you ate. The reading should be less than 180 mg/dL. Just before bedtime.  A target range for someone with diabetes is 110 to 150 mg/dL. You don't want to go to bed with blood glucose that is too low, because that puts you at risk of having a severe low blood sugar episode during the night.

Blood Glucose Level Ask Your Doctor
If your blood glucose before breakfast is lower than 90 mg/dL, that may be too low.  Ask your doctor if you should eat a small snack before you go to bed or reduce your bedtime dose of long-acting insulin. You might want to do a 3:00 am blood glucose check.
If the reading before breakfast is over 130 mg/dL, and several 3:00 am readings are in your target range, you may be experiencing "Dawn Phenomenon".This happens when levels of growth hormone begin to rise in the early morning hours, stimulating the liver to release glucose into the bloodstream.

Ask your doctor if your supper or bedtime NPH insulin dose needs to be increased, or if you would do better using a different type of insulin.

Sometimes, only an insulin pump can address Dawn Phenomenon.

If the reading before breakfast is over 130 mg/dL, and several 3:00 am readings are below 80 mg/dL, you may be experiencing "Rebound Hyperglycemia".

If blood sugar falls rapidly during the night, the liver may be triggered into releasing glucose into the bloodstream. Sometimes when this happens, too much glucose is released. 

This effect may be caused by too much supper or bedtime insulin.  Ask your doctor about reducing the dose.

Ask your doctor about splitting the evening insulin into two separate doses. Take the fast-acting insulin with supper, and wait for bedtime to take the long-acting insulin. Studies show that people who split their evening insulin dose have fewer episodes of nighttime low blood glucose.

If the reading before breakfast is over 130 mg/dL, and the 3:00 am readings are above the target range, your bedtime insulin dose may need to be increased. Often, 1 or 2 additional units of insulin at bedtime can bring the morning blood glucose readings to target levels.
If the reading before lunch or dinner is over 130 mg/dL, that's too high. The insulin dose taken at breakfast or lunch was too small in relation to the carbs you ate.  Ask your doctor about a dose adjustment, or reduce the number of carbs in that meal.
If your blood glucose 2 hours after eating is less than 80, that's too low.

Did you cut back on a meal, or skip it completely? It is important to eat the carbs that are listed in your meal plan in order to be in balance with the insulin you take.

Did you exercise a lot after eating?  Tell your doctor if you regularly exercise after a meal, so that your insulin dose for that meal can be reduced.

If the reading 2 hours after eating is over 180 mg/dL, that's too high. The meal contained too much carbohydrate in relation to the amount of insulin. Either reduce the carb count, or increase the insulin dose to cover the higher carb count.
If your blood glucose is often lower than 110 mg/dL at bedtime, and your fasting blood glucose in the morning is often lower than 80 mg/dL, that's too low.

Ask your doctor if your supper and bedtime insulin doses need to be lowered, or split into two separate doses.

Studies show that people who split their evening insulin dose have fewer episodes of nighttime low blood glucose. Also, you may need a larger bedtime snack.

If your bedtime level is above 150 mg/dL, that's too high. You may need to cut down on food at supper, or increase your supper insulin dose, or cut back on evening snacks - especially high-carb foods like chips, crackers and cookies.

Many doctors ask their patients to report the following information.  Ask your doctor if you should report them, too:

  • A severe low blood sugar that requires treatment by another person

  • Blood sugar consistently running below 70–80 more than 2–3 times in a row

  • More than one unexplained low blood sugar reaction in a week

  • Blood sugars consistently higher than 300 (more than 2–3 days)

  • If you are ill with nausea, vomiting, diarrhea or fever

Do not worry if one reading is out of range by a small amount. However, if a number of readings are out of target, then look for a pattern. Does the blood glucose tend to be too high or low at the same time each day? If you spot a pattern, ask your doctor whether you need to adjust your food intake, your exercise, or your medications.


The BD Diabetes Learning Center describes the causes of diabetes, its symptoms, and diabetes complications such as retinopathy and neuropathy. This site contains detailed information about blood glucose monitoring, insulin injection and safe sharps disposal. Interactive quizzes, educational literature downloads and animated demonstrations help to teach diabetes care skills.

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