Hyperglycemia is defined as blood glucose (sugar) levels that are higher than the target values for the majority of people with diabetes:

  1. above 7 mmol/L, fasting or before a meal
  2. above 10 mmol/L, two hours after the begining of a meal

Hyperglycemia occurs when the amount of insulin in the blood is insufficient or ineffective. When glucose circulating in the blood cannot enter the cells because of a lack of insulin, it accumulates in the blood and raises a person’s glycemia (blood glucose levels) .


Some people may not notice their hyperglycemia. However, above a certain threshold, high blood sugar can lead to the following symptoms:

  • drowsiness
  • increased urination
  • intense thirst
  • excessive hunger
  • involuntary weight loss
  • irritability
  • dizziness


The primary causes of hyperglycemia are:

  • a diet abnormally high in carbohydrates
  • reduced physical activity
  • insufficient insulin  and/or antidiabetic medication (dosage error or a skipped dose)
  • physical stress (illness, surgery, infection, etc.) or psychological stress (mourning a death, new job, moving, etc.)
  • taking certain drugs (e.g.: cortisone)

Hyperglycemia can also be caused by two lesser known phenomena: the dawn phenomenon and the Somogyi effect.

Preventing hyperglycemia

In most cases, hyperglycemia can be avoided by taking the following precautions:

  • Measure your blood glucose (sugar) levels regularly.
  • Follow a daily meal plan designed by a dietitian.
  • Take your insulin or antidiabetic medication as prescribed.
  • Adjust your insulin dose based on your medical prescription


If you experience hyperglycemic symptoms, you should:

  • take your blood glucose (sugar) readings frequently
  • if you have type 1 diabetes: if your blood glucose level is higher than 14 mmol/L, check for ketones in your urine or blood
  • drink water regularly to prevent dehydration
  • adjust your insulin as medically prescribed
  • identify the cause of the hyperglycemia and take appropriate measures, if possible

Emergency situations

Call a doctor or get to Emergency if:

  • your blood glucose reading is higher than 14 mmol/L with ketones
    • in your urine: a “medium” to “high” level
    • in your blood: a level higher than 1.5 mmol/L
  • if you have type 1 diabetes: your blood glucose level is higher than 20 mmol/L with nausea, vomiting and/or abdominal pain
  • if you have type 2 diabetes: your blood glucose level is higher than 25 mmol/L with excessive drowsiness
  • you cannot retain liquids due to vomiting or diarrhea
  • your state of consciousness changes: confusion, agitation, lack of reaction to stimulation, hallucinations or unusual behaviour
  • you exhibit signs of dehydration: dry mouth, sunken eyes, dry skin, etc.
  • your body temperature has stayed above 38.5 °C for more than 48 hours.

These symptoms could signal a hyperglycemic emergency.

Research and text: Diabetes Québec Team of Health Care Professionals

June 2014 (updated on August 2018)

©All rights reserved Diabetes Quebec


S.A. Imran et al. Diabetes Canada 2018 Clinical Practice Guidelines for the Prevention and Management of Diabetes in Canada: Targets for Glycemic Control. Can J Diabetes 2018; 42 (Suppl 1): S42-S46.

Geoffroy L., and Gonthier, M., (2012) “L’hyperglycemia et l’acidose diabétique,” Le diabète chez l’enfant et l’adolescent, 2nd edition,. Montréal: Éditions du CHU Ste-Justine, pp. 355-364.