High blood sugar means that the level of sugar in your blood is higher than normal. It is the main problem caused by diabetes.
The medical term for high blood sugar is hyperglycemia. Blood sugar is also called glucose.
Blood sugar that stays high is the main problem of diabetes. If you have type 1 diabetes, high blood sugar happens because your body is not making insulin. Insulin moves sugar from the blood into your cells. It is normally made by the pancreas. If you have type 2 diabetes, high blood sugar usually happens because the cells have become unable to use the insulin your body is making. In both cases high levels of sugar build up in the blood.
Sometimes people with diabetes can have high blood sugar even if they are taking diabetes medicine. This can happen for many reasons but it always means that your diabetes is not in good control. Some reasons why your sugar might go too high are:
Usually high blood sugar causes no symptoms, especially if it is brief. However, if the blood sugar rises to 300 milligrams per deciliter (16.7 millimoles per liter) or higher and stays that high for a day or longer, you may have symptoms. Symptoms may include:
Very high blood sugar—that is, a blood sugar level of 600 mg/dL (33.3 mmol/L) or higher--can cause coma and even death.
The level of sugar in your blood can be measured with a blood test. The test should be done before breakfast, after several hours of no food or drink except water. This is called a fasting blood sugar test or fasting blood glucose test.
The hemoglobin A1C test is another way of measuring blood sugar. The A1C ("A-one-C") is a way of looking at your average blood sugar control over the past 2 or 3 months. The A1C percentage rises as your average blood sugar level rises. The blood sugar goal for most adults with diabetes is an A1C below 7%.
The treatment depends on the cause.
Type 2 diabetes can be treated with:
Type 1 diabetes occurs when the body (pancreas) stops making insulin. It is treated by giving the body more insulin.
Ask your healthcare provider what you should do if your blood sugar goes over your target, or ideal, range. If you have diabetes, your provider may have you adjust your medicine, exercise, or diet. If you have prediabetes, it is important for you to learn how a healthy diet and regular exercise can help you keep from having type 2 diabetes. This type of diabetes is preventable.
Very high blood sugar above 400 mg/dL (22.2 mmol/L) can be a medical emergency. It must be treated right away with IV (intravenous) fluids and insulin. You may need to stay several days at the hospital to get your blood sugar back to normal and to treat any problems caused by the high blood sugar. Doctors will look for the cause of the high blood sugar. The cause can vary from an infection to not taking your medicine properly. Severe high blood sugar usually happens if:
How long high blood sugar lasts depends on why it happened and how well you follow the directions for controlling it.
High blood sugar can be serious if it's not treated. If your blood sugar runs too high over time, it can cause problems with your heart, eyes, kidneys, nerves, and circulation (blood vessels). A very high blood sugar can cause life-threatening problems, coma, or death. If you have type 1 diabetes, untreated high blood sugar can result in a dangerous complication called ketoacidosis (a buildup of acids in your blood). This is life-threatening but it is preventable. It usually happens only if you have type 1 diabetes. Check your urine for these acids, called ketones, when your blood sugar is high (if your provider recommends it). If there are ketones in your urine, let your provider know right away because ketones are a warning sign that your diabetes is out of control. This problem needs emergency treatment at the hospital.
High blood sugar caused by medicines you are taking usually goes away when you stop taking the medicine.
You should make sure you understand why your blood sugar is high. Follow your healthcare provider's directions carefully to keep your blood sugar normal. This usually means you need to:
Not keeping your blood sugar at normal levels can cause very serious problems. It increases your risk of heart and blood vessel disease, stroke, kidney problems, and loss of vision.
If you have diabetes, talk to your healthcare provider and ask:
If you don’t have diabetes but there are others in your family who have high blood sugar or type 2 diabetes, you should:
If you have fasting blood sugar levels in the prediabetes range—that is, 100 to 125 mg/dL—your level of blood sugar can go back to normal with a healthy diet and regular exercise. This will help you avoid type 2 diabetes. But the potential for developing type 2 diabetes is always there.
If you do have diabetes, follow your healthcare provider's recommendations for: