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Diabetes Health Center

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Diabetes-Related High and Low Blood Sugar Levels - Topic Overview

High blood sugar occurs when the sugar (glucose) level in your blood rises above normal. Eating too many calories, missing medicines (insulin or pills), or having an infection or illness, injury, surgery, or emotional stress can cause your blood sugar to rise.

High blood sugar usually develops slowly over a period of hours to days. But missing a dose of insulin can cause a rapid rise in blood sugar levels. Blood sugar levels just above your target range may make you feel tired and thirsty. If your blood sugar level stays higher than normal for weeks, your body will adjust to that level, and you may not have as many symptoms of high blood sugar.

Unless you don't monitor your blood sugar regularly or you don't notice the symptoms of high blood sugar, you usually will have time to treat high blood sugar so that you can prevent high blood sugar emergencies. Three things can help you prevent high blood sugar problems:

  • Test your blood sugar often, especially if you are sick or are not following your normal routine. You can see when your blood sugar is above your target range, even if you don't have symptoms of high blood sugar such as increased thirst, increased urination, and fatigue. Then you can treat it early, preventing an emergency.
  • Call your doctor if you have frequent high blood sugar levels or if your blood sugar level is consistently staying above your target range. Your medicine may need to be adjusted or changed.
  • Drink extra water or noncaffeinated, non-sugared drinks so you will not be dehydrated. If your blood sugar continues to rise, your kidneys will increase the amount of urine produced, and you can become dehydrated.

Complications of high blood sugar can cause serious problems, including coma and death. Over time, high blood sugar can damage your eyes, heart, kidneys, blood vessels, and nerves.

Low blood sugar occurs when the sugar (glucose) level in your blood drops below what your body needs. Not eating enough food or skipping meals, taking too much medicine (insulin or pills), exercising more than usual, or taking certain medicines that lower blood sugar can cause your blood sugar to drop rapidly. Do not drink alcohol if you have problems recognizing the early signs of low blood sugar.

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