What Are the Signs of High and Low Blood Sugar?
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What Are the Signs of High and Low Blood Sugar?

What Are the Signs of High and Low Blood Sugar?
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Updated on August 6, 2025
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One of the challenges of diabetes management is maintaining consistent blood sugar (glucose) levels. They can fluctuate even when you’re being careful.

And it’s not just carb intake that can cause your blood sugar to spike or drop. In fact, emotional stress and certain medications can increase your levels, while a boost in activity can cause them to drop, says Megan O’Neill, CDCES, a medical science liaison for diabetes care at the healthcare company Abbott in Monterey, California.

Sometimes, people experience a spike in their blood sugar early in the morning because of the “dawn phenomenon,” a temporary surge of hormones that occurs as the body prepares to wake.

“Levels that are too low or high can result in complications that affect your kidneys, heart, and vision, reduce your quality of life, require expensive interventions, or even be fatal,” O’Neill says. The more prepared you are to spot the signs of high and low levels, the better able you’ll be to quickly and easily bring them back within a desired range and stay healthy.

Signs of High Blood Sugar (Hyperglycemia)

High blood sugar occurs when the body doesn’t have enough insulin or can’t properly use the insulin it has to shuttle glucose from the bloodstream to the body’s muscles, organs, and tissues for fuel, O’Neill says. As a result, the amount of sugar in the blood builds up.

A few different factors can contribute to hyperglycemia. High-carb foods, failure to take diabetes medications as prescribed, inadequate insulin dosage, and lack of physical activity can all play a role.

Heightened stress levels can also elevate blood sugar. Non-diabetes-related medications are known to raise blood sugar levels, too. These include blood pressure medications, steroids, immunosuppressants, some antineoplastic agents, and certain mental health medications.

  • Frequent urination
  • Blurred vision
  • Thirst
  • More frequent infections
  • Weight loss
High blood sugar can cause these symptoms through various mechanisms. For example, high levels damage blood vessels and nerves throughout the body. They can also cause fluid to accumulate in the eyes. In an attempt to get your blood sugar to a healthier level, your body will often increase urine output.

A blood sugar reading above 180 milligrams per deciliter (mg/dL) is considered above normal and can bring on these symptoms.

 But it’s possible to have high blood sugar without any symptoms, says Athena Philis-Tsimikas, MD, the corporate vice president for the Scripps Whittier Diabetes Institute in La Jolla, California.
Seek emergency medical attention if you have persistent readings above 300 mg/dL, especially when combined with excessive thirst, nausea or vomiting, dizziness, or confusion. You may have diabetic ketoacidosis, a dangerous complication of diabetes in which your body is unable to produce insulin. In severe cases, very high blood sugar levels (well above 300 mg/dL) can result in coma.

Here are some ways to prevent high blood sugar.

  • Take your medications as directed. Missing doses or taking insulin or other diabetes medications at the wrong time can lead to large fluctuations in blood sugar levels, O’Neill says. Apps such as Medisafe can help you stay on top of your medication regimen. The app lets you plug your meds into your calendar and set reminders so you never miss a dose.
  • Eat carbohydrates in moderation. Carb counting can be helpful for people with diabetes.

     To many carbs can lead to hyperglycemia, while too few may contribute to hypoglycemia. You can use apps like the Carb Manager. You can record food, track your carb and calorie intake, monitor weight loss, and log workouts.
  • Exercise regularly with your doctor’s guidance. Exercise can lower blood sugar in the short term by using glucose for fuel. It can also help you manage your blood sugar over the long term by increasing insulin sensitivity, or how well your body responds to insulin. Consider working with a certified diabetes care and education specialist (CDCES) to come up with an individualized exercise plan. There are also plenty of exercise apps and free online resources you can use to get started.

How Do You Treat Hypoglycemia?

How Do You Treat Hypoglycemia?

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Signs of Low Blood Sugar (Hypoglycemia)

Low blood sugar levels happen when you have too little glucose left in your bloodstream. It most often occurs when you don’t eat enough food, especially carb-containing foods. It can also happen if you’re taking blood-sugar-lowering medications or exercising a lot, O’Neill says. Levels can decrease gradually or suddenly.

When the amount of glucose in the bloodstream drops too low, the body reacts by releasing epinephrine, also called the fight-or-flight hormone. Epinephrine revs your heart rate and can cause the following signs of low blood sugar:

  • Sweating
  • Shaking
  • Nervousness or feeling anxious
  • Irritability
  • Difficulty concentrating, confusion, and slurred speech, if not enough glucose is able to reach the brain

In extreme cases, a lack of glucose within the brain can lead to seizures, coma, and even death, O’Neill says.

If you have glucose levels lower than 70 mg/dL and are taking diabetes medications that can lower blood sugar, such as insulin, sulfonylureas, or meglitinides, consider following the American Diabetes Association’s (ADA) 15-15 Rule. This rule recommends the consumption of 15 grams (g) of simple carbs, such as 6 or 7 hard candies, 3 glucose tablets, or ½ cup of fruit juice.

 Wait 15 minutes, and then check your levels again. If the number is still low, repeat until you reach at least 70 mg/dL.

You may want to check your blood sugar with a traditional glucometer, not a continuous glucose monitor, given the lag time of the latter.

Once your glucose levels are back to normal, you can go ahead and eat your next scheduled meal or snack, which will help prevent levels from dropping again.

But if your symptoms don’t stop, call your doctor or seek medical attention.

How to Keep Your Blood Sugar Levels Stable

Your quality of life and overall health depend on an active, intentional approach to your blood sugar levels, O’Neill says. Avoiding blood sugar that’s too high or too low will help you avoid adverse symptoms and health complications. Stay within your target range and you’re more likely to feel your best and do whatever you want to do in life, she says.

What’s the right range for you? The answer is slightly different for everyone, and your doctor can help you pinpoint yours. The ADA generally recommends these blood sugar targets:

  • Between 80 and 130 mg/dL before meals
  • Less than 180 mg/dL two hours after meals
The first step to stay in these ranges, and course correct high and low blood sugar levels along the way, is to monitor your blood sugar levels with a glucose meter. Your healthcare provider can advise you on how many times per day you’ll want to check your blood sugar. If you take insulin, they will likely advise you to check before every meal. You may need to check it more frequently if you’re sick, recently changed your diet or exercise routine, or if you’re traveling and will be sitting for longer periods of time.

Your provider may also recommend a continuous glucose monitor, a device that allows you to get readings without finger pricks every few minutes, O’Neill says. It may sound an alarm if your blood sugar spikes or lowers too rapidly.

In general, test your blood sugar regularly, listen to your body, and don’t hesitate to reach out to your doctor.

The Takeaway

  • Blood sugar dips and spikes can be caused by many factors, including food, stress, medications, and physical activity.
  • You need to be able to recognize the symptoms of high blood sugar, or hyperglycemia, in order to get treated on time. Symptoms can include frequent urination, thirst, and blurred vision. If your blood sugar level stays over 300 mg/dL and doesn’t come down, and you’re experiencing nausea or vomiting, dizziness, or confusion, seek emergency medical attention. You may have diabetic ketoacidosis, a serious condition.
  • If you take insulin, sulfonylureas, or meglitinides, you’re more likely to experience low blood sugar (hypoglycemia). The symptoms include sweating, shaking, nervousness, irritability, and confusion.
  • Not everyone with diabetes needs to test their levels frequently. But if you take insulin, you’ll likely need to test your blood sugar several times a day to ensure it’s within a healthy range.

Resources We Trust

Additional reporting by Karen Appold.

EDITORIAL SOURCES
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Resources
  1. Diabetes? Don’t Let ‘Dawn Phenomenon’ Raise Your Blood Sugar. Cleveland Clinic. January 5, 2021.
  2. Hyperglycemia (High Blood Sugar). Cleveland Clinic. March 3, 2023.
  3. Hyperglycemia: Symptoms, Causes, and Treatments. Yale Medicine.
  4. Diabetes Symptoms: When Diabetes Symptoms Aren’t a Concern. Mayo Clinic. June 27, 2023.
  5. Hyperglycemia in Diabetes. Mayo Clinic. April 30, 2025.
  6. Diabetic Ketoacidosis. Mayo Clinic.
  7. Diabetes Management: How Lifestyle, Daily Routine Affect Blood Sugar. Mayo Clinic. January 6, 2024.
  8. Carb Counting and Diabetes. American Diabetes Association.
  9. Hypoglycemia (Low Blood Sugar). Cleveland Clinic. January 31, 2023.
  10. Signs, Symptoms, and Treatment for Hypoglycemia (Low Blood Glucose). American Diabetes Association.
  11. 15-15 Rule. MedlinePlus. January 10, 2025.
  12. Low Blood Glucose (Hypoglycemia). American Diabetes Association.
  13. Monitoring Your Blood Glucose in Diabetes. Diabetes Teaching Center.
  14. Treatment of Low Blood Sugar (Hypoglycemia). Centers for Disease Control and Prevention. May 15, 2024.
  15. Check Your Blood Glucose. American Diabetes Association.
  16. Blood Sugar Testing: Why, When, and How. Mayo Clinic. January 16, 2024.
  17. Continuous Glucose Monitoring. National Institute of Diabetes and Digestive and Kidney Diseases. June 2023.
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Elise M Brett, MD, is a board-certified adult endocrinologist. She received a bachelor's degree from the University of Michigan and her MD degree from the Icahn School of Medicine at Mount Sinai. She completed her residency training in internal medicine and fellowship in endocrinology and metabolism at The Mount Sinai Hospital. She has been in private practice in Manhattan since 1999.

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