When blood glucose levels are out of the normal range, they cause complications. These may include:

In the short-term:

  • Hypoglycemia
  • Hyperglycemia
  • Diabetic ketoacidosis
  • Peripheral artery disease
  • Diabetic foot ulcers

In the long-term:

  • Diabetic retinopathy
  • Diabetic nephropathy
  • Cardiovascular disease
  • Stroke
  • Diabetic neuropathy

Careful control of diabetes can reduce your risk of complications.


Hypoglycemia is low blood sugar, usually 50-60 milligrams per deciliter (mg/dL) or 2.8-3.3 millimoles per liter (mmol/L). It can be caused by any of the following:

  • Taking too much insulin for the amount of food you ate
  • Taking too much insulin to treat "fasting" blood sugar
  • Skipping a meal or eating a smaller meal than usual without lowering your insulin dose
  • Exercising harder or longer than normal without lowering your insulin dose

Hypoglycemia can be managed fairly easily if you are able to recognize the symptoms and treat it right away. The symptoms of hypoglycemia include:

  • Shakiness
  • Sweating
  • Rapid heart rate
  • Anxiety
  • Lightheadedness
  • Headache
  • Hunger
  • Pale skin color
  • Sudden moodiness or behavior change, such as crying for no apparent reason
  • Clumsy or jerky movements
  • Confusion or difficulty paying attention
  • Tingling sensations around the mouth
  • Seizures
  • Passing out leading to coma

If you think you are hypoglycemic, test your blood with your blood glucose monitor. If your blood glucose level is below your normal range, treat the hypoglycemia. (If you do not know what your normal blood sugar range is, ask your doctor). Or, if you recognize the symptoms of low blood sugar, you may want to treat it immediately, without waiting to test.

If you are just starting treatment, you may feel some of these symptoms when your blood sugar level is close to the normal range for you. This is called relative hypoglycemia. This happens because your body is adjusting from a high blood sugar level to a lower, more normal level. In this case, it is important that you test your level if you feel these symptoms. By testing your blood sugar, you can avoid treating a normal level.

If you have had diabetes for a long time or have frequent hypoglycemia, you may lose the ability to sense hypoglycemia with these symptoms. This is called hypoglycemia unawareness. It is very dangerous. With your doctor's approval, you will also need to check your blood sugar before driving an automobile or operating machinery to ensure safety.


The goal of treating hypoglycemia is to quickly raise your blood glucose level to within your normal range. This can be done by eating or drinking some form of sugar, such as:

  • 1-2 glucose tablets or the equivalent of glucose gel
  • 4 ounces of fruit juice or cola (15 grams of carbohydrates)—In general, 15 grams of carbohydrates should raise blood sugar 25-50 mg/dL (1.4-2.8.mmol/L)
  • 3 graham crackers (15 grams of carbohydrates)
  • 5-6 pieces of hard candy

Always carry some form of medical alert identification. It can alert others that you have diabetes.

To immediately treat hypoglycemia, you should always have some type of sugar with you.

Wait 10-15 minutes after eating the sugar, and then retest your blood glucose. If it is still too low, repeat the treatment.

If you pass out from hypoglycemia or do not respond to a snack, you will need immediate treatment. This can be an injection of glucagon. Glucagon is a hormone that raises the level of blood sugar. Ask your doctor for a prescription so that you can have it on hand. Also, teach your family members and coworkers how to administer the glucagon. If glucagon is not available, you should be taken to the hospital for emergency treatment. Once successfully treated, you need to try to identify the reasons that caused the condition so that you know how to prevent future recurrences.


Hyperglycemia is high blood sugar. Long-term hyperglycemia is the major cause of many of the long-term complications that occur in people with diabetes (discussed below) though short-term hyperglycemia can cause a life-threatening condition called diabetic ketoacidosis . Hyperglycemia occurs when you do not have enough insulin to dispose of the glucose in your body. It can be caused by any of the following:

  • Taking too little insulin for the food that you ate
  • Eating without taking any insulin
  • Eating a larger meal than usual without adjusting the insulin dose
  • Exercising more or less than you planned without adjusting the insulin dose
  • Being stressed from an illness or life events (may require adjusting the insulin dose)

Hyperglycemia should be treated immediately to avoid further complications. Ask your doctor how often you should check your blood sugar.

The symptoms of hyperglycemia include:

  • High levels of sugar in your urine—ask your doctor if you should be monitoring your urine
  • Frequent urination (polyuria)
  • Increased thirst (polydipsia)
  • Blurred vision

If hyperglycemia is not promptly treated, it can lead to ketoacidosis. When there is not enough insulin around, blood sugar levels rise, and the body breaks down stored fat into acids, instead. The by-products of fat breakdown are ketone bodies, which are acids that build up in the blood that can be toxic.


If your blood sugar is unusually high for more than several hours, check your urine for ketones using a urine ketone kit. If you have ketones, you will need either to consult your doctor immediately or follow a previously agreed plan for managing ketosis. In most cases, the treatment for high blood sugar and urine ketones will be additional insulin and increasing your water intake.

If you often have hyperglycemia, talk with your doctor about the best way to prevent it. You may need to adjust your diet and your insulin regimen.

Diabetic Ketoacidosis

People with type 1 diabetes can develop ketoacidosis, a serious condition that rarely happens in people with type 2 diabetes . When your body is not getting enough insulin, sugar cannot get into the cells to generate energy. When this happens, the body starts breaking down stored fat for energy. The by-products of fat breakdown are ketone bodies, which are acids that build up in the blood that can cause ketoacidosis. The most common reasons for your body to generate ketones are generally the same for hyperglycemia with the following addition: taking too little insulin when you are sick with an infection, the body may need more insulin. This is the setting in which ketoacidosis typically occurs.


Signs and symptoms that signal ketoacidosis include:

  • High levels of ketones in the urine or blood
  • Fruity smell to the breath
  • Abdominal pain
  • Nausea and vomiting
  • Dry mouth or signs of dehydration
  • Fatigue
  • Reduced mental function and alertness
  • Shortness of breath
  • Coma

Generally, the treatment for ketoacidosis is more insulin and fluids. You may need to get the fluid by IV.

Ask your doctor for a plan on when to measure and call about ketones. Ketoacidosis is a life-threatening condition and needs immediate medical treatment.

Diabetic Retinopathy

Chronic high blood sugar, as well as high blood pressure , can damage tiny blood vessels in the retina of the eye. Diabetes is the most common cause of blindness in individuals between the ages of 20-60 in the United States. This damage, called diabetic retinopathy , usually occurs over a long period of time. Signs of eye damage include:

  • Blurry or double vision
  • Rings, flashing lights, or blank spots
  • Dark or floating spots
  • Pain or pressure in one or both of your eyes
  • Trouble seeing things out of the corners of your eyes

Some people do not have any symptoms until the damage is significant. Therefore, it is essential to see your eye doctor regularly for a dilated eye exam at least yearly. Diabetic retinopathy can be treated with laser therapy, called photocoagulation, or surgery. Quitting smoking and controlling your high blood pressure are also important preventive measures.

Other eye conditions occur almost twice as often and at a younger age in people with type 1 diabetes than in people without this disease. These are cataract and glaucoma . A cataract is a cloud over the lens of your eye. Your lens, which is usually clear, focuses light onto the retina, but a cataract makes your vision cloudy. This condition can be treated with surgery.

Glaucoma is caused by increased pressure in the eye that damages your eye's main nerve, the optic nerve. The damage first causes you to lose sight from the sides of your eyes. Without treatment, glaucoma can lead to blindness. Glaucoma can be treated with special eye drops or laser surgery.

Diabetic Nephropathy

High blood sugar and high blood pressure damage the kidneys’ glomeruli, which are responsible for filtering waste out of the blood. This damage allows protein to leak out of the glomeruli and causes wastes that otherwise would be excreted with the urine to build up in your blood. Having small amounts of protein in the urine is called microalbuminuria. Your doctor will order a urine test yearly to monitor for this. Two classes of drugs, angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers, can reduce the leakage of protein in the urine and delay the onset of diabetic nephropathy .

As damage continues, more protein is leaked and more wastes build up. Having larger amounts of protein in the urine is called proteinuria or macroalbuminuria. Eventually, this damage can progress to kidney failure , which requires dialysis or a kidney transplant . Restricting protein intake in diabetic patients with chronic renal failure can lower the death rates.

Cardiovascular Disease

People with type 1 diabetes are more likely to have and die from cardiovascular disease than people without diabetes.

Having diabetes can cause your blood cholesterol levels to rise, leading to clogged, narrowed arteries ( atherosclerosis ). Clogged arteries make it more difficult for blood to carry oxygen and other essential nutrients to vital organs and tissues, such as your heart, and can cause:

  • Chest pain (also called angina )—This pain or pressure feeling usually starts in your chest and radiates to your arm and may worsen when you exercise or after a full meal. People with long-term diabetes may not have chest pain. They need to be aware of other signs like sudden weakness or shortness of breath.
  • Heart attack —This is caused by the blockage of a blood vessel that supplies oxygen and other essential nutrients to your heart. When part of your heart muscle doesn't receive the nutrients it needs to function, it stops working. Symptoms include chest pain or pressure feeling, nausea, indigestion, extreme weakness, and sweating. Symptoms may be blunted in people with chronic diabetes.
  • Cardiomyopathy —This is a weakening of the heart muscle caused by the narrowing of small blood vessels throughout the heart.
  • Peripheral artery disease (PAD) of the lower extremities—Blood flow to the lower body is reduced, which can lead to other problems, like pain, fatigue, tingling, swelling, or muscle weakness. PAD complications increase the risk of other cardiovascular disorders and functional disability.


Type 1 diabetes makes you 2-4 times more likely to have a stroke . A stroke is caused by a blockage of blood flow to the brain. The effects of a stroke depend on the part of your brain that is damaged and may include:

  • Sudden weakness or numbness of your face, arm, or leg on one side of your body
  • Sudden confusion, trouble talking, or trouble understanding
  • Sudden lightheadedness, loss of balance, or trouble walking
  • Sudden trouble seeing in one or both eyes or sudden double vision
  • Sudden severe headache

Diabetic Neuropathy

Many people with diabetes have mild-to-severe forms of diabetic nerve damage, called diabetic neuropathy . Having high blood sugar for many years can damage the blood vessels that bring oxygen to nerves. High blood sugar can also hurt the covering on the nerves. Damaged nerves may stop sending messages, or, they may send messages too slowly or at the wrong times.

Nerve damage due to diabetes could manifest as:

Your feet are especially vulnerable to the effects of type 1 diabetes. Damage to the peripheral nerves, which go to the arms, hands, and legs, as well as the feet, can impair your experience of sensations such as pain, heat, and cold. In addition to nerve damage, type 1 diabetes can also cause a decrease in blood flow. If you have a blister or sore on your foot, you may not feel it because of neuropathy. Then, because of poor blood flow, the sore may not heal and be at a higher risk of becoming infected. In severe cases, this nerve damage can lead to foot and leg amputations . Because of this, it is essential to wash and examine your feet daily. When you have a doctor's appointment, remember to remove your socks and shoes so that your feet can be examined.

If you are at high risk for foot ulcers, checking the temperature of your feet, using an infrared skin thermometer, may reduce the number of ulcers. Products like the TempTouch thermometer are available.

Reduce Your Risk of Complications

Have Regular Checkups

Your doctors can often spot early signs of complications. Perhaps more importantly, most of the complications listed above can be prevented be following recommended standards for diabetic care.

If you have had diabetes for several years, your doctor may recommend that you:

  • Have frequent (every 3-6 months) measurements of glycosylated hemoglobin (Hba1c) to ensure effective treatment.
  • Have yearly eye exam using drops to dilate the pupils.
  • Have periodic foot exam with a nylon monofilament to determine that sensation is normal.
  • Have yearly urine test to detect microalbuminuria.
  • Have careful control of blood pressure, low-density lipoproteins (LDLs), and triglycerides to reduce long-term risk of heart disease and stroke. Talk with your doctor about the right ranges for you.
  • Have yearly flu and periodic pneumococcal vaccines to reduce the risk of pneumonia .
  • Take low-dose aspirin every day, depending on your age and risk factors.

Unfortunately, many people fail to achieve these targets. As a result, complication rates for diabetes are higher than they might otherwise be.

Strive to Keep Healthy Ranges

It is important that you know what your normal ranges are for:

  • Blood sugar levels
  • Blood pressure levels

Work with your doctor to determine healthy ranges for you.

If you have any of these warning signs, contact your doctor right away:

  • Vision problems, such as blurriness or spots
  • Tiredness
  • Pale skin color
  • Numbness or tingling feelings in hands or feet
  • Repeated infections or slow healing of wounds
  • Chest pain
  • Vaginal itching
  • Constant headaches
  • Cuts or blisters on your feet

Revision Information

  • Reviewer: EBSCO Medical Review Board James P. Cornell, MD
  • Review Date: 09/2018 -
  • Update Date: 09/08/2015 -