Symptoms of high blood sugar or low blood sugar usually develop before a diabetic coma.

High blood sugar (hyperglycemia)

If your blood sugar level is too high, you may have:

• Increased thirst
• Frequent urination
• Blurred vision
• Tiredness or weakness
• Headache
• Nausea and vomiting
• Shortness of breath
• Stomach pain
• Fruity breath odor
• A very dry mouth

Low blood sugar (hypoglycemia)

If your blood sugar is too low, you may have:

• Shakiness
• Anxiety
• Tiredness or drowsiness
• Weakness
• Sweating
• Hunger
• A feeling of tingling on your skin
• Dizziness or lightheadedness
• Headache
• Difficulty speaking
• Blurry vision
• Confusion
• Loss of consciousness

Some people, especially those who've had diabetes for a long time, develop a condition known as hypoglycemia unawareness. That means they don't have warning symptoms that signal a drop in blood sugar.

If you have any symptoms of high or low blood sugar, test your blood sugar right away. Based on the test results, follow your diabetes treatment. If you don't start to feel better quickly, or you start to feel worse, get medical care right away.

A diabetic coma is a medical emergency. If you have symptoms of high or low blood sugar and you think you might pass out, call 911 or your local emergency number.

If you're with someone with diabetes who has passed out, call for emergency help. Tell the emergency personnel that the unconscious person has diabetes.

Blood sugar that's either too high or too low for too long may cause the following serious health problems, all of which can lead to a diabetic coma.

• Diabetic ketoacidosis. If your muscle cells become starved for energy, your body may start breaking down fat for energy. This process forms toxic acids known as ketones. If you have ketones (measured in blood or urine) and high blood sugar, the condition is called diabetic ketoacidosis. If it's not treated, it can lead to a diabetic coma.

  Diabetic ketoacidosis is most common in people who have type 1 diabetes. But it can also occur in people who have type 2 diabetes or gestational diabetes.

• Diabetic hyperosmolar syndrome. If your blood sugar level goes above 600 milligrams per deciliter (mg/dL), or 33.3 millimoles per liter (mmol/L), the condition is called diabetic hyperosmolar syndrome.

  When blood sugar is very high, the extra sugar passes from the blood into the urine. That triggers a process that draws a large amount of fluid from the body. If it isn't treated, this can lead to life-threatening dehydration and a diabetic coma.

• Hypoglycemia. Your brain needs sugar (glucose) to function. In severe cases, low blood sugar (hypoglycemia) may cause you to pass out. Low blood sugar can be caused by too much insulin or not enough food. Exercising too vigorously or drinking too much alcohol can have the same effect.

Anyone who has diabetes is at risk of a diabetic coma, but the following factors can increase the risk:

• Insulin delivery problems. If you're using an insulin pump, you have to check your blood sugar frequently. Insulin delivery can stop if the pump fails or if the tubing (catheter) becomes twisted or falls out of place. A lack of insulin can lead to diabetic ketoacidosis.
• An illness, trauma or surgery. When you're sick or injured, blood sugar levels can change, sometimes significantly, increasing your risk of diabetic ketoacidosis and diabetic hyperosmolar syndrome.
• Poorly managed diabetes. If you don't monitor your blood sugar properly or take your medications as directed by your health care provider, you have a higher risk of developing long-term health problems and a higher risk of diabetic coma.
• Deliberately skipping meals or insulin. Sometimes, people with diabetes who also have an eating disorder choose not to use their insulin as they should, in the hope of losing weight. This is a dangerous, life-threatening thing to do, and it raises the risk of a diabetic coma.
• Drinking alcohol. Alcohol can have unpredictable effects on your blood sugar. Alcohol's effects may make it harder for you to know when you're having low blood sugar symptoms. This can increase your risk of a diabetic coma caused by hypoglycemia.
• Illegal drug use. Illegal drugs, such as cocaine, can increase your risk of severe high blood sugar and conditions linked to diabetic coma.

If it is not treated, a diabetic coma can lead to permanent brain damage and death.

Good day-to-day control of your diabetes can help you prevent a diabetic coma. Keep these tips in mind:

• Follow your meal plan. Consistent snacks and meals can help you control your blood sugar level.
• Keep an eye on your blood sugar level. Frequent blood sugar tests can tell you whether you're keeping your blood sugar level in your target range. It also can alert you to dangerous highs or lows. Check more frequently if you've exercised. Exercise can cause blood sugar levels to drop, even hours later, especially if you don't exercise regularly.
• Take your medication as directed. If you have frequent episodes of high or low blood sugar, tell your health care provider. You may need to have the dose or the timing of your medication adjusted.
• Have a sick-day plan. Illness can cause an unexpected change in blood sugar. If you are sick and unable to eat, your blood sugar may drop. While you are healthy, talk with your doctor about how to best manage your blood sugar levels if you get sick. Consider storing at least a week's worth of diabetes supplies and an extra glucagon kit in case of emergencies.
• Check for ketones when your blood sugar is high. Check your urine for ketones when your blood sugar level is over 250 mg/dL (14 mmol/L) on more than two consecutive tests, especially if you are sick. If you have a large amount of ketones, call your health care provider for advice. Call your health care provider immediately if you have any level of ketones and are vomiting. High levels of ketones can lead to diabetic ketoacidosis, which can lead to coma.
• Have glucagon and fast-acting sources of sugar available. If you take insulin for your diabetes, have an up-to-date glucagon kit and fast-acting sources of sugar, such as glucose tablets or orange juice, readily available to treat low blood sugar levels.

• Consider a continuous glucose monitor, especially if you have trouble maintaining stable blood sugar levels or you don't feel symptoms of low blood sugar (hypoglycemia unawareness).

  Continuous glucose monitors are devices that use a small sensor inserted underneath the skin to track trends in blood sugar levels and send the information to a wireless device, such as a smart phone.

  These monitors can alert you when your blood sugar is dangerously low or if it is dropping too fast. But you still need to test your blood sugar levels using a blood glucose meter even if you're using one of these monitors. Continuous glucose monitors are more expensive than other glucose monitoring methods, but they may help you control your glucose better.

• Drink alcohol with caution. Because alcohol can have an unpredictable effect on your blood sugar, have a snack or a meal when you drink alcohol, if you choose to drink at all.
• Educate your loved ones, friends and co-workers. Teach loved ones and other close contacts how to recognize the early symptoms of blood sugar extremes and how to give emergency injections. If you pass out, someone should be able to call for emergency help.
• Wear a medical identification bracelet or necklace. If you're unconscious, the bracelet or necklace can provide valuable information to your friends, co-workers and emergency personnel.

If you experience a diabetic coma, it is very important that it's diagnosed as soon as possible. The emergency medical team will do a physical exam and may ask those who are with you about your medical history. If you have diabetes, it's a good idea to wear a medical identification bracelet or necklace.

Lab tests

At the hospital, you may need lab tests to measure:

• Your blood sugar level
• Your ketone level
• The amount of nitrogen, creatinine, potassium and sodium in your blood

Diabetic coma requires emergency medical treatment. The type of treatment depends on whether your blood sugar level is too high or too low.

High blood sugar

If your blood sugar level is too high, you may need:

• Intravenous fluids to restore water to your body
• Potassium, sodium or phosphate supplements to help your cells work correctly
• Insulin to help your body absorb the glucose in your blood
• Treatment for any infections

Low blood sugar

If your blood sugar level is too low, you may be given a shot of glucagon. This will cause your blood sugar level to quickly rise. Intravenous dextrose also may be given to raise blood glucose levels.

A diabetic coma is a medical emergency that you won't have time to prepare for. If you feel symptoms of extremely high or low blood sugar, call 911 or your local emergency number to make sure help is on the way before you pass out.

If you're with someone with diabetes who has passed out or is acting strange, possibly as if they have had too much alcohol, call for immediate medical help.

What you can do in the meantime

If you have no training in diabetes care, wait for the emergency care team to arrive.

If you are familiar with diabetes care, test the unconscious person's blood sugar and follow these steps:

• If the blood sugar level is lower than 70 mg/dL (3.9 mmol/L), give the person an injection of glucagon. Do not try to give fluids to drink. Do not give insulin to someone with low blood sugar.
• If the blood sugar level is above 70 mg/dL (3.9 mmol/L) wait for medical help to arrive. Don't give sugar to someone whose blood sugar isn't low.
• If you called for medical help, tell the emergency care team about the diabetes and what steps you've taken, if any.