Woman checking her blood sugar levels after experiencing symptoms of high blood sugar

Symptoms Of High Blood Sugar

Written on December 20, 2023 by Amy Harris, MS, RN, CNM. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.

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Many of us know the symptoms of low blood sugar (lightheadedness, feeling “hangry,” and having difficulty concentrating), but what about the other extreme? What are the symptoms of high blood sugar? Learning the symptoms of high and low blood sugar can help you choose the best types of food to keep your blood sugar in a more stable, healthy range without big spikes up or down.

What Is High Blood Sugar?

When you eat more calories and food than your body can process, use, or store right away, your body can’t keep up. For example, after eating an entire bag of sugary candy at the movies, your blood sugar or blood glucose levels spike above your normal level—this is hyperglycemia.

Glucose is a type of sugar produced and stored by your liver that is your body's primary energy source. Think of glucose as being like the gasoline that fuels your car. Close to 50% to 80% of glucose circulating in your bloodstream is used by your brain, kidneys, and red blood cells for fuel. What’s left over helps power all the individual cells in your body.[1]

What Are the Symptoms Of High Blood Sugar?

The symptoms of having high blood sugar can range from subtle to hard to ignore. Most people with hyperglycemia experience [2-4]:

  • Frequent peeing
  • Excessive thirst
  • Increased hunger
  • Blurred vision
  • Headache

If you have frequent episodes of high blood sugar, or you have untreated diabetes or prediabetes, you may notice some of the later consequences of chronic hyperglycemia, such as [2]:

  • Fatigue
  • Slow-healing cuts and sores
  • Skin infections
  • Vaginal yeast infections
  • Weight loss

Many people don’t experience symptoms until their blood sugar is 250 mg/dL or higher. People with diabetes tend to notice the signs of hyperglycemia later than people without diabetes.[2]

Can You Have High Blood Sugar If You Don’t Have Diabetes?

Yes. Anytime your blood sugar levels spike above 100 milligrams per deciliter (mg/dL) for those without diabetes or 140 mg/dL within two hours of eating, you have reached hyperglycemia [4]. That said, people with diabetes are much more likely to experience hyperglycemia than people without.[2]

The difference is that people with either type 1 or 2 diabetes reach these hyperglycemic levels more quickly, easily, and frequently than people without diabetes. Your pancreas, an organ in your digestive tract, secretes a hormone called insulin, which works to break down and store the energy from the food you eat as glucose. High blood glucose in people with diabetes happens because the body has too little insulin or the body can't use insulin properly.[4]

Some other hormonal conditions and diseases can cause hyperglycemia in people who don’t have diabetes. Some of the alternate causes of hyperglycemia besides diabetes are [2,5]:

  • PCOS (polycystic ovarian syndrome)
  • Physical stress, such as from an illness, surgery, or injury
  • Acute emotional stress, such as experiencing trauma or work-related stress
  • Cushing Syndrome
  • Cystic Fibrosis
  • Pregnancy
  • Some inherited genetic conditions that cause insulin resistance
  • Problems with your pancreas (pancreatic cancer, autoimmune conditions, pancreatitis)

All of these conditions can change the way your body processes glucose and can lead to temporary or more frequent spikes in your blood sugar.

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Too Much of A Good Thing—The Health Risks of Hyperglycemia

Occasional episodes of binging on candy when your sugar cravings hit are not necessarily life-threatening or going to cause diabetes overnight. However, chronic hyperglycemia, meaning that your blood glucose levels are frequently above the normal, healthy range, can be bad for your health in the long run. Some of the problems caused by chronic hyperglycemia are [1-4]:

  • Diabetic ketoacidosis (DKA) or diabetic coma (a potentially life-threatening reaction to hyperglycemia, common in people with diabetes)
  • Peripheral neuropathies
  • Poor wound healing/chronic wounds
  • Retinopathy (leading to vision problems)
  • Coronary artery disease
  • Cerebral vascular disease
  • Chronic kidney disease

Hyperglycemia can be a serious problem if you don't treat it, so it's important to know whether your blood sugar levels are consistently high. Checking something called HbA1C can help you better understand trends in your blood sugars over time.

What Does Your HbA1C Tell You About Your Hyperglycemia?

Prediabetes is the intermediate step between having normal blood sugar levels and having consistently high blood sugar levels.[6] Healthcare providers diagnose pre-diabetes in several ways but usually use lab tests such as HbA1c, fasting blood sugar, and a 2-hour post-load glucose test.[6]

HbA1c is also known as A1c or glycated hemoglobin. Hemoglobin is part of your red blood cells. HbA1c testing measures how much blood sugar, or glucose, is attached to your hemoglobin (expressed as a percentage).

Because red blood cells typically only live for around three months, HbA1c results provide information about your average blood sugar level over the last 90 days. If you have prediabetes, diabetes, or other related conditions, this test can tell how well your treatment may be working for you.

Testing Your HbA1c at Home

Even if you don’t have diabetes, knowing your HbA1C can still provide helpful information about how your body puts the food you eat to work. Everlywell offers a convenient, at-home HbA1c test so that you can know whether your blood sugars have been trending toward unhealthy levels over the past three months.

If you have been experiencing some of the symptoms of high blood sugar, testing your HbA1C on your own could provide further clinical evidence. Your symptoms may be your body’s way of telling you that it is the right time to chat with a healthcare provider about your blood sugar levels and how they could be impacting your health.

Is Falling Asleep After Eating Sugar A Sign of Diabetes?

What Is Polyuria?

Is Gestational Diabetes Genetic?


  1. Hantzidiamantis PJ, Lappin SL. Physiology, Glucose. [Updated 2022 Sep 19]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan. Available from: https://www.ncbi.nlm.nih.gov/books/NBK545201/. Accessed December 12, 2023.
  2. Hyperglycemia (High Blood Sugar). Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/9815-hyperglycemia-high-blood-sugar. Published March 2, 2023. Accessed December 11, 2023.
  3. Hyperglycemia in diabetes – symptoms and treatment. Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/hyperglycemia/symptoms-causes/syc-20373631. Published August 20, 2022. Accessed December 11, 2023.
  4. Hyperglycemia (High Blood Glucose). American Diabetes Associaiton. https://diabetes.org/living-with-diabetes/treatment-care/hyperglycemia. Accessed December 12, 2023.
  5. Goyal N, Kaur R, Sud A, Ghorpade N, Gupta M. Non diabetic and stress induced hyperglycemia [SIH] in orthopaedic practice: what do we know so far? J Clin Diagn Res. 2014;8(10):LH01-LH3. doi:10.7860/JCDR/2014/10027.5022.
  6. Echouffo-Tcheugui J and Selvin, E. Prediabetes and What It Means: The Epidemiological Evidence. Annual Review of Public Health 2021 42:1, 59-77. https://doi.org/10.1146/annurev-publhealth-090419-102644.

Amy Harris, MS, RN, CNM has a master's degree in Maternal and Child Health from Harvard T. Chan School of Public Health. She attended Yale School of Nursing and Boston University School of Public Health to become a certified nurse midwife (CNM). She has worked for over 20 years in clinical and public health practice. She specializes in women's reproductive health care, healthy literacy, and writing about health and wellness.

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