High blood sugar, or hyperglycemia, is an excess amount of glucose in the blood. The normal range for blood glucose is 80-120 mg/dL. Hyperglycemia causes symptoms when glucose values are elevated above 200 mg/dL, according to the Mayo Clinic. Hyperglycemia occurs when the body has too little insulin or cannot utilize insulin properly to process the glucose. Eating too much during a meal, not getting enough exercise, emotional stress and physical stresses such as illness can cause high blood sugar levels.
Increased Hunger
When blood sugar levels are too high, glucose spills into urine without being reabsorbed by the body. If glucose is not reabsorbed, the sugar cannot be made available to body cells and thus cannot be used for energy. This lack of energy signals the body to go into starvation mode, which is a hunger response paired with a slowing of the metabolism. Excessive hunger, known as polyphagia, becomes the result.
Frequent Urination
High blood sugar levels create a need for blood to be filtered more frequently in an attempt to remove excess glucose. The kidneys must work extra hard to remove this glucose. This additional filtration leads to an increased need to urinate as well as larger volumes of urine, known as polyuria.
Excessive Thirst
Since there is such a high amount of fluid lost during hyperglycemia due to polyuria, the body becomes dehydrated. Dehydration triggers the body's thirst response in an attempt to keep the fluid balance normal. Excessive thirst is defined by Medline Plus as an abnormally strong need to drink fluid that may be the result of a physical or emotional disease. Increased thirst following a period of lack of fluid intake is not considered excessive. Extreme thirst is called polydipsia.
Fatigue
Although there is a large amount of glucose available in the blood, during hyperglycemic episodes the body is unable to utilize it for energy. The lack of ability to use glucose leads to lack of energy, as glucose is the sugar that the body converts to energy. Because of this, fatigue often results.
Blurred Vision
Excess levels of sugar in the blood cause the eye's lens to swell, which results in blurred vision. The lens cannot shrink to normal size until blood sugar is returned to normal. Fluctuations in vision are often reported as blood sugar levels rise and fall.
