High blood sugar, also called hyperglycemia, affects people who have diabetes. Several factors can play a role in hyperglycemia in people with diabetes. They include food and physical activity, illness, and medications not related to diabetes. Skipping doses or not taking enough insulin or other medication to lower blood sugar also can lead to hyperglycemia.

It's important to treat hyperglycemia. If it's not treated, hyperglycemia can become severe and cause serious health problems that require emergency care, including a diabetic coma. Hyperglycemia that lasts, even if it's not severe, can lead to health problems that affect the eyes, kidneys, nerves and heart.

Hyperglycemia usually doesn't cause symptoms until blood sugar (glucose) levels are high — above 180 to 200 milligrams per deciliter (mg/dL), or 10 to 11.1 millimoles per liter (mmol/L).

Symptoms of hyperglycemia develop slowly over several days or weeks. The longer blood sugar levels stay high, the more serious symptoms may become. But some people who've had type 2 diabetes for a long time may not show any symptoms despite high blood sugar levels.

Early signs and symptoms

Recognizing early symptoms of hyperglycemia can help identify and treat it right away. Watch for:

• Frequent urination
• Increased thirst
• Blurred vision
• Feeling weak or unusually tired

Later signs and symptoms

If hyperglycemia isn't treated, it can cause toxic acids, called ketones, to build up in the blood and urine. This condition is called ketoacidosis. Symptoms include:

• Fruity-smelling breath
• Dry mouth
• Abdominal pain
• Nausea and vomiting
• Shortness of breath
• Confusion
• Loss of consciousness

Seek immediate help from your care provider or call 911 if:

• You have ongoing diarrhea or vomiting, and you can't keep any food or fluids down
• Your blood glucose levels stay above 240 mg/dL (13.3 mmol/L) and you have symptoms of ketones in your urine

During digestion, the body breaks down carbohydrates from foods — such as bread, rice and pasta — into sugar molecules. One of the sugar molecules is called glucose. It's one of the body's main energy sources. Glucose is absorbed and goes directly into your bloodstream after you eat, but it can't enter the cells of most of the body's tissues without the help of insulin. Insulin is a hormone made by the pancreas.

When the glucose level in the blood rises, the pancreas releases insulin. The insulin unlocks the cells so that glucose can enter. This provides the fuel the cells need to work properly. Extra glucose is stored in the liver and muscles.

This process lowers the amount of glucose in the bloodstream and prevents it from reaching dangerously high levels. As the blood sugar level returns to normal, so does the amount of insulin the pancreas makes.

Diabetes drastically reduces insulin's effects on the body. This may be because your pancreas is unable to produce insulin, as in type 1 diabetes. Or it may be because your body is resistant to the effects of insulin, or it doesn't make enough insulin to keep a normal glucose level, as in type 2 diabetes.

In people who have diabetes, glucose tends to build up in the bloodstream. This condition is called hyperglycemia. It may reach dangerously high levels if it is not treated properly. Insulin and other drugs are used to lower blood sugar levels.

Many factors can contribute to hyperglycemia, including:

• Not using enough insulin or other diabetes medication
• Not injecting insulin properly or using expired insulin
• Not following your diabetes eating plan
• Being inactive
• Having an illness or infection
• Using certain medications, such as steroids or immunosuppressants
• Being injured or having surgery
• Experiencing emotional stress, such as family problems or workplace issues

Illness or stress can trigger hyperglycemia. That's because hormones your body makes to fight illness or stress can also cause blood sugar to rise. You may need to take extra diabetes medication to keep blood glucose in your target range during illness or stress.

Long-term complications

Keeping blood sugar in a healthy range can help prevent many diabetes-related complications. Long-term complications of hyperglycemia that isn't treated include:

• Cardiovascular disease
• Nerve damage (neuropathy)
• Kidney damage (diabetic nephropathy) or kidney failure
• Damage to the blood vessels of the retina (diabetic retinopathy) that could lead to blindness
• Feet problems caused by damaged nerves or poor blood flow that can lead to serious skin infections, ulcerations and, in some severe cases, amputation
• Bone and joint problems
• Teeth and gum infections

Emergency complications

If blood sugar rises very high or if high blood sugar levels are not treated, it can lead to two serious conditions.

• Diabetic ketoacidosis. This condition develops when you don't have enough insulin in your body. When this happens, glucose can't enter your cells for energy. Your blood sugar level rises, and your body begins to break down fat for energy.

  When fat is broken down for energy in the body, it produces toxic acids called ketones. Ketones accumulate in the blood and eventually spill into the urine. If it isn't treated, diabetic ketoacidosis can lead to a diabetic coma that can be life-threatening.

• Hyperosmolar hyperglycemic state. This condition occurs when the body makes insulin, but the insulin doesn't work properly. Blood glucose levels may become very high — greater than 600 mg/dL (33.3 mmol/L) without ketoacidosis. If you develop this condition, your body can't use either glucose or fat for energy.

  Glucose then goes into the urine, causing increased urination. If it isn't treated, diabetic hyperosmolar hyperglycemic state can lead to life-threatening dehydration and coma. It's very important to get medical care for it right away.

To help keep your blood sugar within a healthy range:

• Follow your diabetes meal plan. If you take insulin or oral diabetes medication, be consistent about the amount and timing of your meals and snacks. The food you eat must be in balance with the insulin working in your body.
• Monitor your blood sugar. Depending on your treatment plan, you may check and record your blood sugar level several times a week or several times a day. Careful monitoring is the only way to make sure that your blood sugar level stays within your target range. Note when your glucose readings are above or below your target range.
• Carefully follow your health care provider's directions for how to take your medication.
• Adjust your medication if you change your physical activity. The adjustment depends on blood sugar test results and on the type and length of the activity. If you have questions about this, talk to your health care provider.

Your health care provider sets your target blood sugar range. For many people who have diabetes, Mayo Clinic generally recommends the following target blood sugar levels before meals:

• Between 80 and 120 milligrams per deciliter (mg/dL) (4.4 and 6.7 millimoles per liter (mmol/L)) for people age 59 and younger who have no medical conditions other than diabetes
• Between 100 and 140 mg/dL (5.6 and 7.8 mmol/L) for:
  • People age 60 and older
  • Those who have other medical conditions, such as heart, lung or kidney disease
  • People who have a history of low blood sugar (hypoglycemia) or who have difficulty recognizing the symptoms of hypoglycemia

For many people who have diabetes, the American Diabetes Association generally recommends the following target blood sugar levels:

• Between 80 and 130 mg/dL (4.4 and 7.2 mmol/L) before meals
• Less than 180 mg/dL (10 mmol/L) two hours after meals

Your target blood sugar range may differ, especially if you're pregnant or you have other health problems that are caused by diabetes. Your target blood sugar range may change as you get older. Sometimes, reaching your target blood sugar range can be a challenge.

Home blood sugar monitoring

Routine blood sugar monitoring with a blood glucose meter is the best way to be sure that your treatment plan is keeping your blood sugar within your target range. Check your blood sugar as often as your health care provider recommends.

If you have any symptoms of severe hyperglycemia — even if they seem minor — check your blood sugar level right away.

If your blood sugar level is 240 mg/dL (13.3 mmol/L) or above, use an over-the-counter urine ketones test kit. If the urine test is positive, your body may have started making the changes that can lead to diabetic ketoacidosis. Talk to your health care provider about how to lower your blood sugar level safely.

Hemoglobin A1C test

During an appointment, your health care provider may conduct an A1C test. This blood test shows your average blood sugar level for the past 2 to 3 months. It works by measuring the percentage of blood sugar attached to the oxygen-carrying protein in red blood cells, called hemoglobin.

An A1C level of 7% or less means that your treatment plan is working and that your blood sugar was consistently within a healthy range. If your A1C level is higher than 7%, your blood sugar, on average, was above a healthy range. In this case, your health care provider may recommend a change in your diabetes treatment plan.

For some people, especially older adults and those with certain medical conditions, a higher A1C level of 8% or more may be appropriate.

How often you need the A1C test depends on the type of diabetes you have and how well you're managing your blood sugar. Most people with diabetes receive this test 2 to 4 times a year.

Home treatment

Talk to your health care provider about managing your blood sugar. Understand how different treatments can help keep your glucose levels within your target range. Your health care provider may suggest the following:

• Get physical. Regular exercise is often an effective way to control blood sugar. But don't exercise if you have ketones in your urine. This can drive your blood sugar even higher.
• Take your medication as directed. If you develop hyperglycemia often, your health care provider may adjust the dosage or timing of your medication.
• Follow your diabetes eating plan. It helps to eat smaller portions and avoid sugary beverages and frequent snacking. If you're having trouble sticking to your meal plan, ask your health care provider or dietitian for help.
• Check your blood sugar. Monitor your blood glucose as directed by your health care provider. Check more often if you're sick or if you're concerned about severe hyperglycemia or hypoglycemia.
• Adjust your insulin doses. Changes to your insulin program or a supplement of short-acting insulin can help control hyperglycemia. A supplement is an extra dose of insulin used to help temporarily correct a high blood sugar level. Ask your health care provider how often you need an insulin supplement if you have high blood sugar.

Emergency treatment for severe hyperglycemia

If you have signs and symptoms of diabetic ketoacidosis or hyperosmolar hyperglycemic state, you may be treated in the emergency room or admitted to the hospital. (4p4) Emergency treatment can lower your blood sugar to a normal range. Treatment usually includes:

• Fluid replacement. You'll receive fluids — usually through a vein (intravenously) — until your body has the fluids it needs. This replaces fluids you've lost through urination. It also helps dilute the extra sugar in your blood.
• Electrolyte replacement. Electrolytes are minerals in your blood that are necessary for your tissues to work properly. A lack of insulin can lower the level of electrolytes in your blood. You'll receive electrolytes through your veins to help keep your heart, muscles and nerve cells working the way they should.
• Insulin therapy. Insulin reverses the processes that cause ketones to build up in your blood. Along with fluids and electrolytes, you'll receive insulin therapy — usually through a vein.

As your body returns to normal, your health care provider will consider what may have triggered the severe hyperglycemia. Depending on the circumstances, you may need additional tests and treatment.

If you have trouble keeping your blood sugar within your target range, schedule an appointment to see your health care provider. Your provider can help you make changes to better manage your diabetes.

Here's information to help you get ready for your appointment and know what to expect from your health care provider.

What you can do

• Be aware of any pre-appointment restrictions. If your health care provider is going to test your blood sugar, you may need to stop eating or drinking anything but water for up to eight hours before your appointment. When you're making an appointment, ask if there are any restrictions on eating or drinking.
• Write down key personal information, including any major stresses or recent life changes.
• Make a list of all medications, vitamins and supplements you take.
• Create a record of metered glucose values. Give your health care provider a written or printed record of your blood glucose values, times and medication. Using the record, your health care provider can recognize trends and offer advice on how to prevent hyperglycemia or adjust your medication to treat hyperglycemia.
• Write down questions to ask your health care provider. If you need more information about your diabetes management, be sure to ask.
• Check if you need prescription refills. Your health care provider can renew your prescriptions while you're at the appointment.

For hyperglycemia, questions you may want to ask include:

• How often do I need to monitor my blood sugar?
• What is my target range?
• How do diet and exercise affect my blood sugar?
• When do I test for ketones?
• How can I prevent high blood sugar?
• Do I need to worry about low blood sugar? What are the symptoms I need to watch for?
• Will I need follow-up care?

Sick-day planning

Illness or infections can cause your blood sugar to rise, so it's important to plan for these situations. Talk to your health care provider about creating a sick-day plan. Questions to ask include:

• How often should I monitor my blood sugar when I'm sick?
• Does my insulin injection or oral diabetes pill dose change when I'm sick?
• When should I test for ketones?
• What if I can't eat or drink?
• When should I seek medical help?