Hyperglycemia or high blood sugar basics

By Jenilee Matz, MPH Nov 06, 2023 • 7 min

Hyperglycemia (high blood sugar) affects people who have diabetes.

What is high blood sugar?

In diabetes, the body loses its ability to control blood glucose (sugar) levels. This causes blood sugar to rise above what's considered normal. Here you'll learn more about high blood sugar.

What is hyperglycemia?

Hyperglycemia is when the level of sugar in the blood is higher than it should be. It's a common problem in people with diabetes. Diabetes develops when the body doesn't make enough insulin or can't use the insulin it makes properly. Insulin is a hormone that helps move glucose from the blood into the cells, where it's used for energy. Without enough insulin, glucose stays in the blood, and you're considered to have "high blood sugar." Over time, elevated sugar levels can lead to complications that can affect the whole body, such as heart disease, stroke, kidney problems, blindness and nerve damage.

What is considered high blood sugar?

Blood sugar levels are considered high when they're above your individual blood sugar target range. Ask your healthcare provider what your target blood sugar levels should be. Also, be sure to understand what actions you should take when your blood sugar levels are high for you. Following your diabetes treatment plan as prescribed can help keep your blood sugar levels in the normal range.

Diabetic ketoacidosis

High blood sugar levels can be a sign of diabetic ketoacidosis (DKA). DKA is a serious condition caused by a lack of insulin in the body. Without enough insulin, the body can't use glucose for energy and, as a result, it begins to break down fat as an alternative energy source. This process makes ketones, which can build up in the blood and make it acidic. DKA happens when the acid levels in your blood get too high. If left untreated, DKA can lead to a coma or death. The condition can happen in anyone with diabetes, but it is more common in people with type 1 diabetes.

Many healthcare providers recommend testing for ketones when blood sugar is above 240 mg/dL. Your provider may have other guidelines for you. Because high levels of ketones in the blood cause ketones to appear in the urine, you can check ketones at home by using a urine test strip. Your provider may also advise you to test for ketones when you are sick or have symptoms of DKA. Early symptoms of DKA include:

  • Increased thirst or a very dry mouth
  • Frequent urination
  • High blood sugar readings
  • High levels of ketones in your urine

Later symptoms can include:

  • Constant tiredness
  • Dry or flushed-looking skin
  • Fruity-smelling breath
  • Trouble breathing
  • Confusion or trouble paying attention
  • Nausea, abdominal pain or vomiting. Once vomiting starts, life-threatening DKA can develop within hours. Note that other illnesses besides DKA can cause vomiting. Contact your healthcare provider when vomiting lasts longer than two hours.

If your blood sugar is high and you have moderate or large amounts of ketones in your urine, these are warning signs that your diabetes is out of control. Contact your healthcare provider if you test positive for ketones.

What are causes of hyperglycemia?

The following factors can cause your blood sugar to rise higher than normal:

  • Not taking enough insulin
  • Eating more or exercising less than planned
  • Illnesses, such as a cold or the flu
  • Emotional stress
  • The dawn phenomenon. Everyone experiences the dawn phenomenon, which is a surge of certain hormones in the early morning hours. These hormones signal the liver to release sugar. People without diabetes can handle this increase in sugar coming from the liver by making more insulin. However, people with diabetes don't have a normal insulin response to account for this surge, so they may experience high blood sugar in the morning.

For some people, high blood sugar may be due to prediabetes. This means that your blood sugar is higher than normal, but not high enough to be considered diabetes. However, prediabetes is a warning sign of diabetes, and many people with the condition go on to develop diabetes.

Signs of hyperglycemia

Symptoms when blood sugar is high include:

  • High blood sugar readings
  • High levels of sugar in the urine
  • Increased thirst
  • Frequent urination
  • Tiredness or weakness
  • Headaches
  • Blurred vision

High blood sugar doesn't always cause clear symptoms, though. Your healthcare provider will likely tell you to test your blood sugar at home regularly. This can help tell if your diabetes treatment plan is working.

Hyperglycemia vs. hypoglycemia

Hypoglycemia is low blood sugar. Like high blood sugar, low blood sugar primarily affects people with diabetes, especially those who use insulin or take oral medicines that help the body make more insulin. Low blood sugar is serious and requires prompt treatment to bring blood sugar levels back to normal levels.

Treating hyperglycemia

Your healthcare provider will prescribe a diabetes treatment plan in an effort to control your blood sugar levels. Diabetes management often involves testing your blood sugar at home, following a healthy eating plan, reaching and maintaining a healthy weight, getting regular exercise, possibly taking insulin or other medicines and keeping up with checkups.

Work closely with your healthcare provider to get high blood sugar levels in check. Doing so can protect your health and reduce your risk of diabetes-related complications.

Clinically reviewed and updated November 2023.

Explore more

7 min
By Andy Stergachis, PhD, RPh
Aug 02
8 min
By Nora Saul, MS, RD, CDE; Updated by: Jen Matz, MPH
Nov 06
7 min
By Jenilee Matz, MPH
Nov 06