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.

Insulin Diabetes medication Exercise Drinking water

While that sounds simple, you do need to know some particulars about each of these methods to bring your levels down safely.

Take Insulin

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).

Intramuscular Injections

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)

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.

Exercise

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.

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.

Drink Water

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.

When to Get Medical Attention

Call 911 or get to an emergency room if you have:

Hyperglycemia and elevated ketone levelsSustained very high blood sugar levelsSymptoms of DKA or HHSTwo blood sugar readings of 300 mg/dL or aboveBlood 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 readingsFrequent urinationHigh 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.

Summary

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.

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