When you have type 1 or type 2 diabetes, dangerous spikes in blood glucose (severe hyperglycemia) may mean you need to reduce blood sugar levels immediately. If you don't, you could be at risk for potentially life-threatening complications.
This article looks at what blood sugar levels are considered dangerous, the symptoms to watch for, the four best ways to quickly lower your blood sugars, and when to contact your healthcare provider—or go to the emergency room.
How High Is Too High?
Any blood glucose level (BGL) above your target range is too high. Your healthcare provider should tell you what your upper limit is, as it may be different for different people.
In general, though:
- 140 milligrams per deciliter (mg/dL) is considered hyperglycemic but not dangerously high
- 180 milligrams per deciliter (mg/dL) is too high and you should take steps to bring it down.
- 240 mg/dL puts you at risk for potentially life-threatening diabetic ketoacidosis (DKA or diabetic coma), especially in type 1 diabetes.
- 600 mg/dL or higher for extended periods can cause the potentially fatal hyperglycemic hyperosmolar syndrome (HHS), especially in type 2 diabetes.
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What to Do About It
You can lower your blood sugars quickly with:
- Diabetes medication
- Drinking water
While that sounds simple, you do need to know some particulars about each of these methods to bring your levels down safely.
The preferred—and quickest—method of treating hyperglycemia is to take rapid-acting insulin such as Humalog, Novolog, or Apidra. If you have type 1 diabetes, you may be able to get a correction dose through your insulin pump, as well.
Slow-acting insulin, such as NPH, does not lower blood sugars quickly. It takes several hours to work. Therefore, it's not an appropriate treatment when you urgently need to bring down your BGL.
Insulin works by moving glucose from your blood into your cells. There, you either use it for fuel right away or your cells store it for later, when you don't have enough ready energy to meet demands.
When the body doesn't have enough insulin (type 1 diabetes) or doesn't use it efficiently (type 2 diabetes), it can lead to short-term symptoms and complications, like DKA and HHS.
Be sure you talk to your healthcare provider about how much rapid-acting insulin you should take to bring down dangerously high BGL.
Once you've had the shot, you'll want to re-check your levels in 15-30 minutes to see whether they're coming down and how fast. Sometimes, levels will go too low and you'll end up with hypoglycemia (low blood sugar levels).
If your BGL doesn't drop right away, or doesn't come down as fast as you'd like, resist the urge to take more insulin too soon, as it could lead to hypoglycemia. It may start working in 15 minutes, or it may take up to an hour.
Types of Insulin and How They Work
Injecting your insulin directly into a muscle can help your body absorb it more quickly. However, it's also more likely to lead to hypoglycemia, which may become severe. It can also cause a potentially fatal insulin overdose.
You should talk to your healthcare team about whether intramuscular injections are a good idea during hyperglycemic episodes. They can also tell you where and how to give yourself this kind of injection.
Take Missed Medication
Many people with diabetes take prescription medications other than or along with insulin. These medications help keep your blood sugar within the normal range.
Missing a dose of these medications can make your BGL high. If you're surprised by a high reading, check to make sure you took your last dose. Keeping them in a daily pill sorter instead of a bottle makes this simple.
However, many diabetes drugs only work if they're taken before you eat. They won't help lower a dangerously high BGL. These include biguanides such as Glucophage (metformin) and alpha-glucosidase inhibitors like Precose (acarbose) and Glyset (miglitol).
Diabetes medications that can bring down your BGL quickly include:
- Meglitinides: Starlix (nateglinide) and Prandin (repaglinide)
- Sulfonylureas: Diabinese (chlorpropamide), Amaryl (glimepiride), Glucatrol (glipizide), Micronase/Glynase (glyburide)
An Overview of Oral Diabetes Medication
Timing of a Makeup Dose
If you miss a dose of your diabetes medication, take it as soon as you remember. But don't double-up by taking your missed medication too closely to your next scheduled dose. This can cause dangerous side effects.
When in doubt, check the medication packaging for guidance, contact your healthcare provider, or talk to a pharmacist. If you miss several doses, contact your practitioner about the best course of action.
Treating the Lows of Hypoglycemia
- BGL between 55 mg/dL and 69 mg/dL: Eat 15 grams of carbohydrates and re-check BGL in 15 minutes.
- BGL below 55 mg/dL: Call 911. Inject Glucagon (glucagon hydrochloride) if available. If conscious, drink juice or a sugary soda, then eat carbohydrates with protein (e.g., cheese and crackers).
What to Do When Your Diabetes Medication Isn't Working
Physical activity is the fastest way to lower your blood sugar without medication. Exercise lowers insulin resistance and helps your body convert glucose into energy.
During muscle contractions, your cells take glucose from your bloodstream and use it for energy. This lowers your blood sugar for 24 hours or more after you exercise.
Check Ketones Before Exercising
If your blood sugar is above 240 mg/dL, check your ketone levels and don't exercise if they're elevated. Exercise can increase ketone levels, which can raise blood sugars and put you more at risk of ketoacidosis.
Everyone responds differently to exercise, so there's no perfect formula for how much to exercise to lower your BGL. In general, though:
- You need to get your heart rate up
- Longer durations of physical activity lower your blood sugar more than short durations
It's a good idea to do regular blood sugar checks before and after working out. That way, you'll have an idea how your body responds under normal circumstances, and that can help guide your decisions the next time you have a dangerously high BGL.
Making a Type 2 Diabetes Exercise Plan
When you have an episode of severe hyperglycemia, water and other unsweetened fluids can help your kidneys flush out excess sugars through your urine. While it may not be as fast as rapid-acting insulin or exercise, it can help get you to a safe BGL.
Staying hydrated may help you prevent hyperglycemic episodes, as well. Most people need about four to six cups of water each day. If you work out frequently or tend to sweat a lot, you may need more. If you take medications that cause fluid retention, you may need less.
Ask your healthcare provider about your daily water needs and about how much to drink if you have a spike in blood sugars.
How Hyperglycemia Is Treated
Causes of Hyperglycemia in Diabetes
- Eating too many carbohydrates
- Not getting enough physical activity
- Illness or infection
- Taking a corticosteroid, like prednisone
- Skipping or not taking enough glucose-lowering medication
When to Get Medical Attention
Call 911 or get to an emergency room if you have:
- Hyperglycemia and elevated ketone levels
- Sustained very high blood sugar levels
- Symptoms of DKA or HHS
- Two blood sugar readings of 300 mg/dL or above
- Blood sugar readings above 180 mg/dL (or your target range) for more than a week
You should contact your healthcare provider for guidance if you have:
- Consistently high blood sugar readings
- Frequent urination
- High levels of sugar in the urine (diagnosed using at-home glucose dipstick test)
- Increased thirst
They'll likely want you to make an appointment to go over treatment and lifestyle options for better managing your illness.
Blood Ketone Meters: How to Test at Home
Any blood glucose level above your target range is too high. In general, 180 mg/dL is considered dangerously high and you should take steps to bring it down.
A BGL of 240 mg/dL puts you at risk for diabetic ketoacidosis. Regular readings of 600 mg/dL or higher could lead to hyperglycemic hyperosmolar syndrome. Both of these conditions can be fatal and require emergency medical treatment.
You can lower blood sugars quickly with rapid-acting insulin, taking missed doses of oral medications such as meglitinides or sulfonylureas, exercising, and drinking water.
Get emergency medical attention for readings in the danger zone plus high ketone levels, sustained high BGL, or symptoms of DKA or HHS. Contact your healthcare provider if you have consistently high levels, increased thirst, or frequent urination.
A Word From Verywell
When your blood sugars are high enough to lead to DKA or HHS, you likely don't feel good already. Getting a bad glucometer reading can send you into a panic. That makes it difficult to take appropriate measures.
Thus, it's important for anyone with diabetes to learn how to handle very high levels before they occur. Be sure to talk about this possibility with your endocrinologist or diabetic educator.
Because you may become confused or unconscious from severe hyperglycemia, it's important to educate the people close to you, as well.
Types of Glucometers and How to Choose the Best One
Frequently Asked Questions
What foods can lower blood sugar quickly?
No foods can do this. If your blood sugar is high, stick with foods that are less likely to raise your blood sugar, such as non-starchy vegetables, meat, cheese, nuts, or avocados. Avoid carbohydrates like bread, potatoes, rice, and fruit.
Learn More:What to Eat When Blood Sugar Is High
What can I drink to lower blood sugar quickly?
Water is the best choice. Excess sugar in the blood is filtered through the kidneys and excreted through urine, and keeping hydrated can help your body expel that sugar faster. Unsweetened, non-carbonated beverages are okay, too. Avoid juice and sweetened beverages.
How long does it take for blood sugar to go down?
It depends on your level and what you're doing to lower it. For example, rapid-acting insulin can start to work in 15 minutes and continues to lower blood sugar for up to four hours. Oral diabetes medications vary by type. Some can take several hours, while others may take days.
Verywell 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.
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By Michelle Pugle
Michelle Pugle, BA, MA, is an expert health writer with nearly a decade of contributing accurate and accessible health news and information to authority websites and print magazines. Her work focuses on lifestyle management, chronic illness, and mental health. Michelle is the author of Ana, Mia & Me: A Memoir From an Anorexic Teen Mind.
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