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Extreme fluctuations in blood sugar (glucose), whether too high ( hyperglycemia ) or too low ( hypoglycemia ), can be dangerous for people with diabetes. The type of diabetes, your medication regimen, your age, the length of time your blood sugar is out of range, and your ability to identify symptoms are some factors that can determine the types of complications a person can have.
Emergencies can arise when abnormal blood sugar levels occur for extended periods and are accompanied by physiological symptoms, such as sweating, shakiness, or confusion with low blood sugar or weight loss, excess hunger, and fruity breath with high blood sugars. However, not everyone has symptoms.
Sometimes, these extremes warrant a trip to the hospital and, if not treated immediately, can cause serious complications, even death.
Because diabetes management relies heavily on the person living with it, it is incredibly important to understand the dangers of very low and very high blood sugar, how to identify them, and what to do about it.
This article will cover when high and low blood sugars are dangerous, what to do immediately, the risks and causes of extreme blood sugars, and when a trip to the hospital for yourself or someone else is warranted.
If you are a person living with diabetes and have experienced low blood sugar, you can attest to how bad it can feel and how frightening it can be when it happens suddenly. Caring for someone with diabetes and seeing them experience low blood sugar can also be scary and overwhelming.
To mitigate fear, it is important to know the signs and symptoms and what to do when it happens.
Hypoglycemia
Symptoms of low blood sugar vary from person to person, but some common symptoms include:
The American Diabetes Association (ADA) defines hypoglycemia in levels based on severity.
Level 1 hypoglycemia is defined as a measurable glucose concentration less than 70 milligrams per deciliter (mg/dL) or 3.9 millimoles per liter (mmol/L) but greater than or equal to 54 mg/dL (3.0 mmol/L).
Level 2 hypoglycemia is defined as a blood glucose concentration less than 54 mg/dL (3.0 mmol/L). This level is considered the threshold at which there is a shortage of glucose or sugar in the brain, resulting in neuroglycopenic symptoms.
A blood sugar this low requires immediate action to resolve symptoms of hypoglycemia. If you experience a blood sugar this low and do not have symptoms, you may have hypoglycemia unawareness. A review of your treatment plan is warranted to prevent reoccurrence.
Level 3 hypoglycemia is defined as a severe hypoglycemia event (recognized or unrecognized) characterized by altered mental and/or physical functioning that requires assistance from another person for recovery. In this instance, you cannot treat your blood sugar on your own.
This type of hypoglycemia is less common and usually impacts people with type 1 diabetes who take insulin. If not treated quickly, this can progress to seizure, loss of consciousness, coma, or death.
High blood sugar can happen occasionally without resulting in harm or damage. But chronically high blood sugars over time can result in diabetes complications whose damages are both microvascular (small vessels) and macrovascular (large vessels).
Blood sugar targets for people with diabetes are individualized and vary based on age, type of diabetes, duration of disease, life expectancy, other health conditions, and low blood sugar risk/awareness.
Hyperglycemia
General blood sugar targets for adults with diabetes include a fasting blood sugar of 80 to 130 mg/dL and less than 180 mg/dL one to two hours after meals. Technically, anything higher than this is high, but this is also very subjective and should be discussed with your healthcare provider.
Cause for concern occurs when blood sugars are repeatedly higher than normal repeatedly (discovered when you identify a pattern) or when blood sugars are elevated and a person has symptoms.
If you notice that you or someone you are caring for has blood sugars above their target values regularly (and can't identify why), you may need a change in the treatment regimen. Contact your diabetes care team, physician, or certified diabetes care and education specialist for education and support.
High blood sugar is considered dangerous when it presents with ketones, which is more common in type 1 diabetes. High blood sugar with ketones can also occur in people with type 2 diabetes treated with insulin or an oral class of medications called sodium–glucose cotransporter-2 (SGLT-2) inhibitors.
High blood sugar can be dangerous when it causes symptoms for people with undiagnosed diabetes. Type 2 diabetes develops gradually, and people can have prediabetes or undiagnosed diabetes without knowing it. Over time, high blood sugar levels can progress to diabetes or cause complications of diabetes.
Some common symptoms of high blood sugar include:
Diabetic ketoacidosis (DKA) and hyperglycemic hyperosmolar nonketotic syndrome (HHNS) or hyperglycemic hyperosmolar nonketotic coma (HHNKC) are diabetes emergencies that occur when blood sugars are at extremely high levels and warrant immediate medical attention.
DKA occurs when insulin is absent, and the body cannot use glucose for fuel. It instead starts to burn fat and produce ketones for energy. It is different from ketosis. DKA causes the blood to become acidic. It warrants immediate medical attention.
From this, cell damage can occur. If it continues to progress, it can cause coma or death.
DKA tends to develop slowly; the first symptoms are usually intense thirst and excessive urination. However, if it is left untreated, more severe symptoms can come on quickly and may include:
When you should check for ketones depends on your individualized diabetes treatment regimen. Many experts advise checking for ketones when your blood glucose is more than 240 mg/dL, while others suggest checking when your blood glucose is more than 300 mg/dL.
For those who use insulin pump therapy, it is advised to test for ketones when blood sugars are greater than 300 mg/dL for no reason or if your blood sugar has not come down in two hours after a correction dose of insulin.
HHNS or HHNKC is more common in people with type 2 diabetes who have an infection, like pneumonia or a urinary tract infection. Although uncommon, this emergency can cause blood sugars to rise above 600 mg/dL. Other symptoms include:
Low blood sugar can be reversed and treated with rapid-acting carbohydrates, such as 4 ounces of juice, 1 tablespoon of sugar or honey, candy, glucose tablets, or glucose gel (read packages for amounts).
The rule of 15-15 recommends treating a low blood sugar with 15 to 20 grams of rapid-acting carbohydrate and retesting in 15 minutes. If blood sugar has not increased to at least 70 mg/dL, you should repeat the treatment until it does.
It's important not to treat with carbohydrates containing fat like chocolate, for example, as this can delay glucose absorption. In addition, people with type 2 diabetes should not eat protein to treat low blood sugar because it may increase insulin response without increasing blood sugar.
Once your blood sugar returns to normal, eat a meal or snack containing carbohydrates and protein (for example, an apple with peanut butter or an egg-vegetable wrap). This will help to prevent your blood sugar from dropping again.
As hard as it might be not to eat as much as you can until you feel better, this technique can backfire and result in rebound hyperglycemia.
Infants, toddlers, and children may need less carbohydrate to treat low blood sugars. Your diabetes treatment team can give you individualized recommendations.
In a severe hypoglycemic event, you may not be able to treat yourself, and someone else will need to administer glucagon. Glucagon is a hormone produced by the pancreas that triggers the release of stored glucose (glycogen) from the liver, fat cells, and muscles.
Parents, school personnel, camp counselors, and anyone else caring for people with diabetes who are prone to low blood sugar, like young children and older adults, should know how to use glucagon.
The ADA states, "Recurrent level 2 hypoglycemia and/or level 3 hypoglycemia is an urgent medical issue and requires intervention with medical treatment plan adjustment, behavioral intervention, and, in some cases, use of technology to assist with hypoglycemia prevention and identification."
The method used to treat high blood sugar will depend on how high your blood sugar is, why it is high, and whether or not ketones are present. For example, if your after-meal blood sugar is elevated due to inaccurate carbohydrate counting and insulin dosing, you may be able to take extra insulin to "correct" it or bring your blood sugar down.
However, if your blood sugar is very high, you are feeling ill, and you have ketones, you should call your healthcare team for medical advice. Treatment methods are highly individualized based on a person's specific needs and situation.
Emergencies like a hypoglycemic event or DKA can result in coma and death. These situations warrant immediate treatment.
Frequent episodes of low blood sugar, particularly in children, are associated with cognitive issues, and older adults may have hypoglycemia unawareness.
When blood sugars are chronically high, they increase the risk of a person developing diabetes complications. In the Diabetes Control and Complications Trial, better glycemic control in people with type 1 diabetes was associated with 50% to 76% reductions in rates of development and progression of complications of the eyes, nerves, and kidneys.
Therefore, it's important to work with your diabetes care team to keep your blood sugars in a healthy range and prevent glucose excursions (fluctuations, especially changes with meals) or glucose variability.
The causes of dangerous blood sugar can be different depending on the type of diabetes you have and the medication you take.
Low blood sugar can occur in someone with diabetes due to various factors, including mistiming medications (taking medicine after a meal or taking too much medicine) or meal skipping. Or, in the case of children with type 1 diabetes, dosing insulin for food that was not eaten. Low blood sugar can also be caused by drinking alcohol and physical activity.
Dangerously high blood sugar is associated with skipping medications like insulin, insulin pump malfunctions, not taking medications as prescribed, and illness.
If you must be hospitalized due to dangerous blood sugar levels, a clinician with expertise in diabetes management should be part of your treatment team. Depending on the reason for hospitalization, correction of high blood sugar, as in DKA, will include hydration, insulin, and electrolyte replacement.
With so many variables that can impact blood sugar, people with diabetes are always at risk of having their blood glucose levels fluctuate.
Prevention of low blood sugar requires careful attention to blood glucose monitoring, food, insulin adjustments, and understanding of events that can cause low blood sugar, like fasting for medical tests, skipped meals, and exercise.
Many people with diabetes benefit from having a continuous glucose monitor. This wearable technology can be programmed to alarm when blood sugar is trending high or low.
Prevention of high blood sugar will also include accurate blood sugar monitoring, following a diabetes-friendly meal plan, exercise, adequate sleep, taking medications as prescribed and managing stress.
The following precautions can help you stay prepared:
The American Diabetes Association calls blood glucose monitoring "an integral component of effective therapy" for people who take insulin." Blood glucose monitoring at home with a blood glucose meter can help to identify causes of increased or reduced blood sugars.
All people who use a continuous glucose monitor (CGM) should also have a blood glucose monitor to confirm high and low blood sugars.
Many variables can impact blood sugar, including diet, exercise, medicine, illness, stress, sleep, and hormones. Any change in one of these variables can increase the risk of high and low blood sugars. Hence, it is important to understand your target values and how to check them, as in blood glucose or continuous glucose monitoring.
Extremely low and high blood sugars can become immediate dangers, and prompt action must be taken. If you are unsure what to do when your blood sugar is too high or too low, you should make an appointment with your diabetes care team or certified diabetes care and education specialist for instruction.
13 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
By Barbie Cervoni, RD
Cervoni is a New York-based registered dietitian and certified diabetes care and education specialist.
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