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Key takeaways
Blood sugar levels above 200 mg/dl are considered dangerous, and individuals with diabetes should aim to stay within their target range to avoid long-term complications.
Hyperglycemia (high blood sugar) can result from various factors, including insufficient insulin, overconsumption of carbohydrates, less physical activity, illness, or stress. If not treated, it can lead to serious conditions like diabetic ketoacidosis (DKA) or hyperosmolar hyperglycemic syndrome (HHS).
The American Diabetes Association recommends checking for ketones if blood sugar exceeds 240 mg/dl, highlighting the importance of regular monitoring and treatment to prevent emergencies.
High blood sugar over extended periods can cause significant health issues, including problems with eyes, feet, skin, nerves, kidneys, and an increased risk of heart attacks, strokes, and amputation, emphasizing the need for controlling blood sugar levels.
If you have Type 1 or Type 2 diabetes, your healthcare provider will recommend that you aim to stay within your target range, or normal range, as much as possible. Doing so is best for your overall health and helps you prevent or delay long-term complications of high blood sugar.
Hypoglycemia is the medical term for low blood glucose levels (or blood sugar levels). Hyperglycemia is the medical term for high blood sugar levels. People with diabetes will see their blood sugar levels rise and fall often, as a result of food, exercise, or other variables. Fluctuating blood sugar levels are normal, as long as they return to the normal range. However, having long periods of high blood sugar can be dangerous, both in the short term and long term. This article will focus on hyperglycemia.
What is a dangerous level of blood sugar?
Hyperglycemia is the medical term for high blood sugar.
Blood sugar levels can spike for a variety of reasons, including:
- Taking too little insulin or oral diabetes medication (or missing a dose)
- The body is not effectively using your natural insulin (insulin decreases blood sugar levels)
- Eating or drinking more carbohydrates than the amount of insulin you injected, or the amount of insulin your body can make
- Less physical activity
- Illness
- Emotional stress
- The dawn phenomenon (this occurs when a hormone surge causes blood sugar to increase in the early morning hours)
- The Somogyi effect (this occurs when blood sugar drops overnight, and the body makes more sugar to compensate, and you wake up with higher blood sugar)
For patients who do not have diabetes, blood sugar may increase due to other conditions or medications, such as endocrine conditions, pancreatic diseases or tumors, certain medications (such as diuretics or steroids), or surgery.
What is a dangerous high level of blood sugar? That may vary slightly by the individual. Your healthcare provider will give you a detailed treatment plan, which will include information about what level of blood sugar is dangerously high for you, and what you should do if it occurs.
The American Diabetes Association recommends that if your blood sugar is higher than 240 mg/dl, you should check your urine for ketones.
Checking blood sugar regularly, or wearing a continuous glucose monitor (CGM), is important for people with high blood glucose due to diabetes or other medical conditions.
High blood sugar can quickly turn into a serious problem if left untreated, so you should treat it as soon as you realize that it is high. Left untreated, high blood sugar can cause diabetic ketoacidosis, or DKA. DKA is more common in people with Type 1 diabetes than Type 2 diabetes, but can still occur in people with Type 2 diabetes. DKA can develop when the body does not have enough insulin. Without enough insulin, the body cannot use glucose for energy, so the body breaks down fats to use for energy. When the body breaks down fats, it makes waste products called ketones. The body tries to eliminate ketones in the urine, but the body cannot get rid of all the ketones, so they build up in the blood, which can lead to DKA. DKA can lead to a diabetic coma or death—it is life-threatening and requires emergency treatment.
Hyperosmolar hyperglycemic syndrome, or HHS, is more common in people with Type 2 diabetes who do not have their diabetes under control. It can occur when blood sugar is high over a long time. Normally, the kidneys try to eliminate excess blood sugar in the urine, but this also causes water loss. If you do not drink enough fluids, you become dehydrated. When this happens, the kidneys can no longer eliminate extra sugar in the urine, and blood sugar levels become very high, sometimes more than 10 times the normal number. HHS is a medical emergency and can cause a coma or death if not treated. People who develop HHS often have very high blood sugar levels, around 600 mg/dl. Along with very high blood sugar, dehydration and decreased alertness or consciousness may occur.
Having high blood sugar over long periods of time can also lead to serious health problems, and long-term complications, such as problems with the eyes, feet, skin, blood pressure, cholesterol, nerves, kidneys, and digestion. Some of these problems can lead to other complications such as heart attack, stroke, or amputation. It is important to control high blood sugar levels as much as possible to prevent both short-term and long-term problems.
What are the signs and symptoms of high blood sugar?
The most common signs and symptoms of high blood sugar include:
- High blood sugar levels (as tested on a meter or CGM)
- High levels of glucose in the urine
- Increased thirst
- Frequent urination
DKA is a medical emergency and requires emergency treatment in a hospital. Symptoms of DKA may include:
- Fruity-smelling breath
- Nausea and vomiting
- Dry mouth
- Shortness of breath
HHS is also a medical emergency and requires emergency treatment. Symptoms of HHS, which may worsen over days or weeks, may include:
- Increased thirst and urination (especially at first)
- Weakness
- Nausea
- Weight loss
- Dry mouth and tongue
- Fever
- Seizures
- Confusion
- Coma
- Problems with movement or speech
- Loss of feeling or function of the muscles
If you are diagnosed with diabetes, or hyperglycemia due to another medical condition, make sure you know the symptoms that require emergency treatment.
Blood sugar chart
The chart below shows normal blood sugar levels by age for individuals with and without diabetes, starting from children less than 6 years old, through adults 20 years and older. These are general guidelines. Your doctor may give you different guidelines, so consult your healthcare provider for more information.
Normal blood sugar levels by age |
|||||
|---|---|---|---|---|---|
| Age | Children < 6 years old | Children 6-12 years old | Adolescents and teenagers 13-19 years old | 20+ years old | |
| Fasting | With diabetes | 80-180 mg/dl | 80-180 mg/dl | 70-150 mg/dl | 80-130 mg/dl |
| Without diabetes | Less than 100 mg/dl | Less than 100 mg/dl | Less than 100 mg/dl | Less than 100 mg/dl | |
| 1-2 hours after eating | With diabetes | ~180 mg/dl | 140 mg/dl or less | 140 mg/dl or less | Less than 180 mg/dl |
| Without diabetes | Less than 120 to 140 mg/dl | Less than 120 to 140 mg/dl | Less than 120 to 140 mg/dl | Less than 120 to 140 mg/dl | |
| Bedtime | With diabetes | 110-200 mg/dl | 100-180 mg/dl | 90-150 mg/dl | 100-140 mg/dl |
| Without diabetes | Less than 100 mg/dl | Less than 100 mg/dl | Less than 100 mg/dl | Less than 100 mg/dl | |
| A1C | With diabetes | <6.5 to 8% depending on the patient | <6.5 to 8% depending on the patient | <6.5 to 8% depending on the patient | <7 to 8%
depending on the patient |
| Without diabetes | <5.7% | <5.7% | <5.7% | <5.7% | |
How to lower your blood sugar quickly
If you need to quickly lower your blood sugar, follow the directions provided by your health care professional. If you use insulin, this is the best way to quickly lower blood sugar. If you take oral diabetes medication, check to see if you missed a dose. You can ask your doctor if you are not sure how much insulin to administer or if you need to take an extra dose of medication.
Exercising can be another effective method of lowering blood sugar. Drinking lots of water can also help decrease blood sugar. There are no foods that will lower your blood sugar quickly, but if your blood sugar is high, you will want to avoid foods that spike blood sugar (such as white rice, pasta, and sweets) until your blood sugar comes back into the normal range.
You can also ask your healthcare provider or another member of your diabetes healthcare team such as your Certified Diabetes Care and Education Specialist (CDCES) about other ways to help lower blood sugar quickly, as well as steps you can take to lower blood sugar in general.
When to see a doctor
Your treatment plan will include information about when you should consult your doctor or when you need to go to the emergency room. Always consult your healthcare provider if you have any questions about your blood sugar, and get emergency medical help if your symptoms are severe or life-threatening. Conditions such as DKA or HHS are life-threatening and can cause coma or death if not treated. If you are not sure what to do, it is better to err on the side of caution and get emergency medical help. And remember to always wear a medical ID to alert first responders to your medical condition.
Frequently asked questions about dangerous levels of blood sugar
What is an alarming high blood sugar level?
An alarming high blood sugar level may vary, based on your target range. Generally, if blood sugar is 240 mg/dl or higher, you will need to test for ketones. Your healthcare provider will give you a full treatment plan that outlines what action needs to be taken for certain ranges of blood sugar. For example, if your target range is 80-130 mg/dl, your healthcare provider may advise you to inject a certain amount of insulin if your blood sugar is 200 mg/dl, or check ketones and contact your doctor if your blood sugar is 240 mg/dl.
What are normal blood sugar levels before and after eating?
For adults with diabetes, a normal range before eating is generally 80-130 mg/dl. For adults without diabetes, a normal blood sugar before eating is less than 100 mg/dl.
A normal blood sugar one or two hours after eating, for someone with diabetes, is usually less than 180 mg/dl. For someone who does not have diabetes, normal blood sugar is less than 120 to 140 mg/dl.
Ask your healthcare provider what numbers you should aim for, as targets vary by individual.
What sugar level starts a diabetic coma?
People with Type 1 diabetes have a greater chance of going into a diabetic coma due to DKA. A diabetic coma due to high blood sugar can occur at blood sugar levels of 300 mg/dl, or more.
People with Type 1 diabetes also have a greater chance of going into a diabetic coma due to severe hypoglycemia (severely low blood sugar).
People with Type 2 diabetes have a greater chance of going into a diabetic coma due to
diabetic hyperosmolar hyperglycemic syndrome (HHS). With HHS, blood sugars can be very high, reaching 600 mg/dl or higher. Left untreated, HHS can cause a coma or death.
Can someone survive a diabetic coma?
Yes, but emergency treatment needs to occur immediately. There is a risk of brain damage or death if there is any delay in responding to a diabetic coma.
Ways to save on insulin
Some people skip doses of medicine or try to ration insulin because they have trouble affording their medications. With several ways to save money, such as choosing generics when available, using manufacturer coupons for brand-name drugs or insulin, or accessing a free SingleCare card, cost should not prevent you from taking medications as prescribed.
If you are having trouble affording your medications or insulin, tell your healthcare professional so they can make some adjustments to your regimen that can be just as effective but more affordable.