High Blood Sugar Symptoms as Warning Signs

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Introduction to High Blood Sugar

High blood sugar, also known as high glucose, results when the concentration of glucose in the bloodstream exceeds 120 mg/dl (milligrams per deciliter). Episodes of high blood sugar are known as hyperglycemia, not to be confused with hypoglycemia, or low blood sugar. According to the Mayo Clinic, blood sugar levels may not cause symptoms until they reach a “significantly elevated” level of higher than 200 mg/dl. High blood sugar left untreated can cause serious health issues, including loss of vision, circulation problems and heart, liver or kidney damage.High blood sugar symptoms will become more serious if they remain untreated or high for long periods of time.

The symptoms of high blood sugar include the following:

Frequent Urination

One of the most common symptoms of blood sugar levels that are too high is the need to urinate more often than usual. This could include having to urinate for no apparent reason (i.e. have not been consuming enough liquid to warrant it). This symptom can be caused by other conditions as well, and should be discussed with a doctor if it persists or appears in combination with any other symptoms.

Unexplained Fatigue

Fatigue is more than feeling tired. It is a lack of energy that even napping cannot seem to correct. When unexplained fatigue occurs (i.e. the patient is not under stress, overworking or ill), it can be a symptom of high blood glucose levels, among other things.

Increased Thirst

One of the earliest and most common symptoms of high blood sugar levels is an increased thirst. People with this symptom feel thirsty frequently throughout the day, sometimes feeling like their thirst is unquenchable. If there is no apparent reason for the patient to be so thirsty so often, it can indicate hyperglycemia.


When blood sugar levels rise, a headache can follow. For some people, it can be one of the first symptoms that is noticeable because it can occur so quickly in response to high blood sugar levels.

Some patients with hyperglycemia will awaken with a high blood sugar headache. This is part of the dawn phenomenon related to diabetes.

Blurred Vision

Blurred vision related to high blood glucose levels can occur sporadically and last for varying amounts of time. If there is no explanation such as other ongoing vision problems or eye irritation, it can be an indicator of hyperglycemia. Regardless of the cause, this symptom should be reviewed with a doctor.

Fruity Breath

When a patient has hyperglycemia, they may have breath that smells fruity, even though they have not consumed anything to cause that odor. This is one of the more easily identifiable symptoms of hyperglycemia.

Dry Mouth

Dry mouth is another symptom related to high blood glucose. It causes the patient to feel very parched, even when they have consumed water or other beverages.


Though confusion can be related to other medical issues, it is one of the common symptoms of high blood sugar levels.


One of the most serious and frightening high blood sugar symptoms, a coma can occur when blood sugar levels become too high for too long. Other symptoms of high blood sugar levels should be addressed before this symptom comes into play.


Hyperglycemia in Diabetes. Mayo Clinic Staff. March 23, 2010. https://www.mayoclinic.com/health/hyperglycemia/DS01168

Hyperglycemia and Diabetes. Diabetes Health Center. Reviewed by John A Seibel, MD. March 8, 2009. WebMD. https://diabetes.webmd.com/diabetes-hyperglycemia

Hyperglycemia (High Blood Glucose). Living with Diabetes. American Diabetes Association. https://www.diabetes.org/living-with-diabetes/treatment-and-care/blood-glucose-control/hyperglycemia.html