The signs of high and low blood sugar

Written by

Lauren Dobischok
13 October, 2022

Medically checked article All HOMED-IQ content is reviewed by medical specialists

Blood sugar is a measurement of the amount of sugar, or glucose, in your blood. This sugar comes from the food you eat and is the body’s main source of energy. Although adequate blood sugar is needed for your body to function, too much sugar in your blood can cause serious damage to your body. This is why keeping your blood sugar levels within a healthy range is important for good health. Blood sugar that is too high is known as diabetes. This can occur when your body does not produce insulin (type I diabetes) or because your body does not make or use insulin well (type II diabetes). Although diabetes is a common condition, the symptoms caused by high or low blood sugar can be difficult to identify or can be confused for other health problems. This is why an estimated 36% of adults in Europe have diabetes but do not know it (IDF, 2021). Being able to identify the signs of abnormal blood sugar levels can help individuals prevent type II diabetes before it occurs, or help diabetics keep their blood sugar in a healthy range. Read on to learn more about the signs of high and low blood sugar.

Measuring blood sugar

Blood sugar levels can be diagnosed and checked in several ways. Individuals with diabetes may measure their blood sugar several times a day using a finger-prick test or a continuous glucose monitor like the Freestyle Libre (CDC, 2021). Checking blood sugar levels throughout the day can help you understand how your body responds to certain foods and how much medication is needed. To diagnose diabetes, the following values apply:

GroupFasting (mmol/L)~2 Hours after eating (mmol/L)
Non-diabetic3.3 – 5.55.0 – 7.8
Prediabetic5.5 – 6.17.8 – 11.1
Type II diabetic> 6.1> 11

In diagnosed diabetics, it is generally recommended to try and keep your fasting blood sugar between 4.5 and 8 mmol/L. A good blood sugar ~2 hours after eating is lower than 9. Therefore, with treatment you should try to keep your blood sugar between 4.5 and 9 mmol/L (Thuisarts, 2022).


A hemoglobin A1C (HbA1C) test measures your average blood sugar level over the past 2-3 months. This test can be used to diagnose diabetes or check if your diabetes is under control. To diagnose diabetes, the following values apply:

GroupHbA1C (%)
Non-diabetic< 6.0
Prediabetic6.0 – 6.5
Type II diabetic> 7.0

In diagnosed diabetics, it is generally recommended to keep your HbA1C level below 7% (Tello, 2020). This target may vary and should be discussed with your healthcare provider. To learn more, read our blog “What is HbA1C?”. It is now also possible to check your HbA1C from home using a self-test, such as Homed-IQ’s Blood Sugar Test or Homed-IQ’s Heart Disease Blood Test. This test allows users to check for potential undiagnosed diabetes or see how well their diabetes is being managed without visiting a doctor. To learn more about the differences between a home HbA1C test and one from the doctor, read our blog “Testing for diabetes – should you perform a home test or see a doctor?”.

Symptoms of high blood sugar

High blood sugar (hyperglycemia) is when the glucose level in your blood is too high. High blood sugar is the primary symptom of type I and II diabetes, but can also occur in people who have certain chronic conditions, are stressed, or are sick. Lack of physical activity, not taking enough insulin (diabetics), eating more than planned, dehydration, an unhealthy diet, and erratic timing of meals can cause high blood sugar (NHS, 2022).

Symptoms of high blood sugar are usually not noticeable at first, and may only appear when levels get very high. Symptoms of high blood sugar are the same as symptoms of untreated diabetes, which results in high blood sugar due to insufficient insulin. Symptoms can include:

  • Extreme thirst
  • Peeing a lot
  • Losing weight
  • Blurred vision
  • Fatigue
  • Recurrent infections, such as thrush, bladder infections, and skin infections

Very high blood sugar levels can cause life threatening complications, such as Diabetic ketoacidosis (DKA). Ketones are a chemical that is produced by the liver when it breaks down fats. Your body uses ketones during fasting, long periods of exercise, and when there are not many carbohydrates available. If your body does not have enough insulin, it will begin to convert fat into energy rather than using blood sugar. Using fat for energy produces ketones, which can build up in the blood and become DKA. This is a medical emergency and must be treated immediately (NHS, 2022).

Symptoms of DKA include:

  • Fruity smelling breath
  • Thirst
  • Fainting
  • Feeling sick
  • Frequent urination
  • Confusion
  • Coma

Symptoms of low blood sugar

Low blood sugar is defined as blood glucose that is below 3.5 mmol/L (CDC, 2021). Low blood sugar is most common in people with type I diabetes, and can be caused by taking too much insulin, not eating enough carbs for your insulin intake, changes in routine, hot weather, and drinking alcohol. 

Symptoms of low blood sugar vary between individuals. In diabetics, it is important to learn your own symptoms of low blood sugar. Symptoms may include:

  • Hunger
  • Dizziness
  • Rapid heartbeat
  • Nervousness
  • Shaking
  • Sweating
  • Irritability or confusion

Some people may not have symptoms of low blood sugar until it is extremely low. This is known as hypoglycemia unawareness and can happen in people who have had diabetes for a long time, frequently have low blood sugar, or who take certain medications (CDC, 2021). Individuals who have hypoglycemia unawareness may need to check their blood sugar more often.

How to regulate blood sugar

Keeping your blood sugar stable is beneficial for those with and without diabetes. Following a healthy diet, maintaining a healthy weight, and exercising regularly are very important in keeping your blood sugar levels in check (CDC, 2021). Additionally, the following tips can also help keep your blood sugar levels stable:

  • Eat a regular times and do not skip meals
  • Limit alcohol and sweets
  • Drink water instead of juice or soda
  • Keep track of your food portions
  • Track your blood sugar levels and see what makes them go up or down (diabetics)


Ik heb diabetes type 2 en mijn bloedsuiker blijft te hoog | Thuisarts.nl. (2021, November 22). thuisarts.nl. Retrieved September 28, 2022, from https://www.thuisarts.nl/diabetes-type-2/ik-heb-diabetes-type-2-en-mijn-bloedsuiker-blijft-te-hoog#wat-is-een-goede-bloedsuiker-bij-diabetes-type-2

Low Blood Sugar (Hypoglycemia). (2021, March 25). Centers for Disease Control and Prevention. Retrieved September 28, 2022, from https://www.cdc.gov/diabetes/basics/low-blood-sugar.html

Manage Blood Sugar. (2021, April 28). Centers for Disease Control and Prevention. Retrieved September 28, 2022, from https://www.cdc.gov/diabetes/managing/manage-blood-sugar.html#:%7E:text=Keep%20track%20of%20your%20blood,%2C%20drink%2C%20and%20physical%20activity.

NHS website. (2022, June 10). High blood sugar (hyperglycaemia). nhs.uk. Retrieved September 28, 2022, from https://www.nhs.uk/conditions/high-blood-sugar-hyperglycaemia/

Tello, M., MD. (2020, October 27). Rethinking A1c goals for type 2 diabetes. Harvard Health. Retrieved September 28, 2022, from https://www.health.harvard.edu/blog/rethinking-a1c-goals-for-type-2-diabetes-2018032613452

About the author

Lauren Dobischok

Lauren is a health scientist and science communicator currently living in the Netherlands. Originally from Canada, she completed a Research Master’s in Health Sciences at the Netherlands Institute of Health Sciences at Erasmus University Rotterdam (NIHES) with a specialisation in epidemiology. Prior to her master’s degree, she completed a Bachelor’s degree in Health Sciences at Simon Fraser University. With a background in public health, her goal is to create accurate scientific content that is easy to understand and empowers people to make informed decisions. Within Homed-IQ, Lauren works as a Product Developer and Content Lead, working closely with physicians and scientists on medical devices for Homed-IQ’s new products and written communications.