Middle of the night. Checking your blood glucose level in the middle of the night is particularly useful for insulin users to determine if blood glucose levels are maintained at a reasonably safe level during the night. This is especially true for those who inject intermediate- or long-acting insulin at suppertime or bedtime, as well as for insulin pump users who wish to evaluate their overnight basal rates. In some cases, if fasting or prebreakfast blood glucose levels are too high, it can be the result of “rebounding” from levels that have dropped too low in the middle of the night.
In response to symptoms. If you have signs or symptoms of low blood glucose (hypoglycemia) or high blood glucose (hyperglycemia), it is best to check your blood glucose level to verify your suspicions that you are low or high before taking any action. Symptoms of low blood glucose include weakness, shakiness, sweatiness, hunger, an increase in heart rate, headache, dizziness, and fatigue. However, if you have symptoms of low blood glucose and cannot check, go ahead and treat yourself for low blood glucose to be on the safe side. Treatment involves eating or drinking 15 grams of carbohydrate, the amount found in 1/2 cup of juice or regular soda, 3 glucose tablets, or 5 or 6 pieces of hard candy. If possible, check your blood glucose again after 15 minutes, and treat again if it is still too low. Repeat these steps until your blood glucose level is at least 70 mg/dl.
Prompt treatment of hypoglycemia is important to prevent seizure or loss of consciousness. However, some people who have had high blood glucose for a long time experience one or more of the symptoms of hypoglycemia when their blood glucose levels drop to more normal levels. In this case, raising blood glucose by consuming carbohydrate is not recommended. While it can be hard to resist the urge to eat something in this situation, it is believed that the brain will readjust to more normal blood glucose levels—and a person will no longer experience symptoms of hypoglycemia—if allowed adequate time.
Many people with diabetes can have blood glucose levels that run significantly higher than recommended without having any symptoms that would alert them to elevated blood glucose levels. This is why regular monitoring is useful, and it’s also why it’s important to monitor if you have symptoms of high blood glucose such as frequent urination, dry mouth, thirst, blurred vision, or fatigue, since your blood glucose level may be very high by the time such symptoms appear. Some possible methods of treating high blood glucose include drinking more water, exercising, changing your diet, and changing the amount or timing of your insulin or diabetes drugs. However, there’s no one quick fix for high blood glucose, so you should work out a plan for responding to it with your diabetes care team at your regular appointments before it happens.
Before or after exercise. Blood glucose monitoring can be beneficial in helping you evaluate the effects of exercise and physical activity on your blood glucose control. It is also important to monitor because exercise can cause blood glucose levels to drop, either during or up to 24 hours after activity. For this reason, you should check your blood glucose before you start to exercise, as well as immediately after the activity, to make sure that it is not too low. In addition, if you experience symptoms of hypoglycemia—such as hunger, nervousness, or shakiness—while exercising, stop and check your blood glucose level. If, in any of these situations, your reading is below 70 mg/dl, you should treat for hypoglycemia, wait 15 minutes, and then check your blood glucose again. It is always a good idea to have a source of carbohydrate on hand when you are exercising.
Blood glucose levels that are too high can also make physical activity dangerous. If your blood glucose is over 300 mg/dl, or if you have Type 1 diabetes and it is over 250 mg/dl and you have ketones in your urine, physical activity can make your blood glucose level go even higher. In these situations, exercise is best avoided.