High Blood Sugar (Hyperglycemia): Symptoms, Causes, and Treatment

Woman with doctor checks her blood sugar (glucose) level.

What is Hyperglycemia?

Hyperglycemia is the medical term for high blood sugar (high blood glucose). It happens when sugar stays in your bloodstream instead of being used as energy.

For people without type 1 diabetes (T1D), a healthy blood sugar level is about 70 to 140 milligrams per deciliter of blood (mg/dL). For people with T1D, though, the target or healthy blood sugar range depends on a number of other factors, like their age, how long they’ve had diabetes, and other health conditions they may have. To achieve good long-term glucose control, people with diabetes should focus on the time they spend in their target range, which is typically 70 to 180 mg/dL.

Doctors may say you have hyperglycemia if your blood sugar is higher than 130 mg/dL after not eating or drinking for at least 8 hours (called fasting hyperglycemia) or if your blood sugar is higher than 180 mg/dL 2 hours after a meal (called postprandial or after-meal hyperglycemia).

For people with type 1 diabetes, blood sugar control over the long term is important. Your healthcare team will work with you to evaluate your long-term control by looking at your HbA1c and/or the amount of time your blood sugar is within your target range based on data from a continuous glucose monitor, or CGM, or your blood glucose meter.

How Does Hyperglycemia Happen?

Insulin is a hormone made by the pancreas that lets your body use the sugar (glucose) in your blood, which comes primarily from carbohydrates in the food that you eat. Hyperglycemia happens when your body has too little insulin to use the sugar in your blood.

People with T1D can have episodes of hyperglycemia every day. Although this can be frustrating, it rarely creates a medical emergency. Not taking enough insulin can lead to hyperglycemia (like missing a dose or not taking enough insulin for the carbs you ate).

Other things that can cause hyperglycemia include:

  • Caffeine
  • Stress
  • Illness
  • Medications
  • Hormone changes
  • Intensive exercise

Also, every day around 4 to 5 am, your body releases hormones as it is getting ready to wake up. These hormones can work against insulin and cause high blood sugar. This is called the “dawn phenomenon.” In people without diabetes, the body releases some extra insulin to deal with that hormone surge; if you have T1D, though, you might not have enough insulin to manage it, so you get hyperglycemia.

How Do I Know if I Have Hyperglycemia?

Signs of hyperglycemia (high blood sugar) include:

  • Being extremely thirsty
  • Urinating (peeing) a lot
  • Feeling very tired
  • Having trouble seeing or concentrating
  • Experiencing stomach pain, nausea, or vomiting
  • Having sweet-smelling or “fruity” breath
  • Cuts or sores that do not heal, infections, and unexplained weight loss may also be signs of long-term hyperglycemia.

If you notice any of these symptoms, you should check your blood sugar. If your blood sugar is very high, you should also test for ketones in either your blood or urine.

What Are The Risks of Hyperglycemia?

Hyperglycemia can be a sign that your body isn’t getting enough insulin. It is normal for patients with T1D to get hyperglycemia, and most of the time this is simply treated with insulin. If the body does not have insulin for approximately 8 hours, you could develop a condition called “diabetic ketoacidosis,” or DKA.

In DKA, your body breaks down fat for energy because it doesn’t have enough insulin to use the sugar in your blood. This produces chemicals called ketones, which make your blood more acidic.

DKA is dangerous. Too much acid in your blood can make you pass out (diabetic coma) or even cause death.

Signs of DKA

Signs of DKA include:

  • Throwing up (vomiting)
  • Difficulty breathing
  • Confusion
  • Extreme sleepiness
  • Sweet-smelling or “fruity” breath

If you notice these or any of the other signs of hyperglycemia listed above, you are at risk of or may already have DKA.

How to Test for Ketones

You can use a urine test strip or blood ketone meter and ketone test strip to test for ketones at home. Testing either urine or blood is important, but when possible, a blood test is preferred because it gives you and your care team more precise information about your ketone levels. Because urine may have been in the bladder for some time, the results from these tests may show levels that are either higher or lower than the ketone levels that are actually circulating in your body. It is also very important to know that urine test trips degrade over time, so if you are using this method, you need to look at expiration dates carefully.

Your diabetes care team can give you specific directions about when you should check for ketones, but in general, you should check for them when your blood glucose is 240 mg/dL or higher. You should also check for ketones if you notice any of the DKA symptoms listed above or if you are sick (like with a cold or the flu); it is possible to have ketones while your blood glucose levels are within range (70-180 mg/dL).

At-home urine test strips will change color to show the level of ketones in the urine. They typically report results as “negative,” “trace,” “small,” “moderate” or “large.” Blood ketone meters will provide a number that indicates the ketone levels. The following ranges are generally used:

  • 0.6 to 1.0 mmol/L is considered normal for people with diabetes
  • 1.0 to 1.5 mmol/L is a range in which it is a good idea to call your diabetes care team
  • 1.5 to 3.0 mmol/L is a sign of DKA risk and indicates that you should call your diabetes care team
  • More than 3.0 mmol/L is considered a medical emergency and indicates that you should go to the emergency room or call 911

You should call your diabetes care team immediately if your urine test results show you that you have moderate or large levels of ketones or your blood ketone test shows 1.5 mmol/L or greater, if you have a high blood glucose reading and symptoms of DKA, or if you have a high blood glucose level that is not getting lower after taking insulin. You should go to the emergency room if you have high levels of ketones and have vomited at least twice in the last 4 hours.

Importantly, if your blood sugar is above 240 mg/dL, you should test for ketones before exercising. The presence of ketones in someone with T1D shows that there’s not enough insulin for the body to use the sugar, so exercise would only burn more fat, make more ketones, and make hyperglycemia worse.

Treating Hyperglycemia

The first thing you should do to treat hyperglycemia is take insulin. Your doctor should explain to you your “correction factor,” which is the amount of insulin you will need to bring your blood sugar level down a certain amount (for example, 1 unit might lower your blood sugar by 50 mg/dL).

If you take insulin by syringe or pen, and your blood sugar has not responded within 2 hours, you can take a second dose (using the same correction dose). Remember that insulin takes 20 to 30 minutes to work and will continue to work for 4 to 5 hours. It’s important not to take too many doses, which can lead to “insulin stacking” and low blood sugar (hypoglycemia).

If you’re using a pump for insulin delivery, follow these steps to bring your blood sugar level down:

  • If you do not have ketones, you should take a dose of insulin through the pump. Wait 1 hour and test your blood sugar again. If it is lower, check your blood sugar before your next meal. Take your next insulin dose at the usual time. If your blood sugar did not go down, take a dose of insulin by syringe or pen and check your blood sugar in 1 hour. Consider changing the infusion site because the insulin might not be absorbing properly and the infusion set or catheter may not be working properly.

  • If you have ketones, take a dose of insulin by syringe or pen. Check your pump and change the infusion set. Check your blood glucose and ketones every hour. Take your next dose of insulin through the pump.

It’s important to drink a lot of water or other carbohydrate-free beverages while treating hyperglycemia, and you should call your doctor if your blood sugar stays high after taking insulin.

If you get hyperglycemia often, talk with your doctor. They might adjust your medication or suggest you talk with a dietitian about meals and exercise. Also, a CGM can help you keep track of changes in your blood sugar throughout the day.

Planning for Sick Days

Your body releases stress hormones when you are sick, which can cause hyperglycemia. Keep taking your insulin and other diabetes medications, even if you are throwing up. If you have ketones and your blood sugar is above 240 mg/dL, call your doctor. They might also want you to call if:

  • You have diarrhea that lasts more than 6 hours
  • You are throwing up (vomiting)
  • You have a high fever or trouble breathing
  • You feel very sleepy or confused

Continue checking your blood sugar levels and keep track of the results.

Exercise and Hyperglycemia

Managing blood sugar during and after physical activity is important and is something that a lot of people with T1D have questions about. JDRF has a number of resources available for people with T1D and their families, many of which can be found here.

Managing your Diabetes Devices

If you are using an insulin pump, talk to your diabetes team about how to best manage hyperglycemia. In general, be sure to check your pump first. Make sure all parts are connected and working correctly. Check your bolus history and temporary basal rate. Also check your insulin to make sure it has not expired or gotten too warm.

If you use a CGM, try not to react to it too often. You might be tempted to give another dose of insulin too soon, before the first one finishes working, which is known as “stacking insulin”; this can cause low blood sugar (hypoglycemia).

Children and Hyperglycemia

Controlling blood sugar is very important in children with T1D. Long-term hyperglycemia damages the eyes, heart, kidneys, and nerves, so it is important to maintain good glucose control to minimize the chances of this damage.

Make a plan with your child’s doctor for meals, exercise, special events, travel, and school activities. Understand that your teen may drink alcohol or skip meals, so you should also understand how these actions may affect your child’s blood sugar. Importantly, they should test their blood sugar before driving a car.

Talk to your child’s teachers, babysitters, coaches, and others about what your child or teen needs to avoid hyperglycemia and stay safe. Click here for a downloadable guide on causes, symptoms and treatments of hyperglycemia.