What is high blood sugar (hyperglycaemia)? Symptoms, causes and prevention

High blood sugar, also called high blood glucose or hyperglycaemia, refers to when there is an excessive amount of sugar in the blood. This is typically caused by a problem in the production or use of insulin as its role is to regulate the amount of blood glucose. Hyperglycaemia is commonly associated with diabetes and can lead to serious health problems if left untreated. This guide will explore hyperglycaemia, highlighting the causes, symptoms, and prevention/treatments available.

What is bone high blood sugar (hyperglycaemia)?

High blood sugar is a medical term meaning there is too much sugar in the blood. This can occur when your body doesn’t have enough insulin or cannot use it properly.

Hyperglycaemia is linked with diabetes, and the levels of blood glucose can indicate how advanced the condition is. As a guideline, the levels of blood sugar and associated diabetes stages are as follow:

Diabetes stage Fasting blood glucose levels
Pre-diabetes >100 mg/dL (milligrams per decilitre)
Diabetes >125 mg/dL (milligrams per decilitre)

Untreated high blood sugar levels can lead to serious problems as it can cause damage to the nerves, blood vessels, organs and other body tissues. It may also increase your risk of heart attacks and stroke.

What are the symptoms of high blood sugar?

Symptoms of high blood sugar gradually develop over time and there may not be any symptoms at all until the blood sugar levels are considerably high. However, common symptoms associated with hyperglycaemia typically include:

  • Increased thirst
  • Dry mouth
  • Frequent need to urinate
  • Unintentional weight loss
  • Blurred vision
  • Tiredness
  • Feeling sick
  • Vomiting
  • Pain in the abdomen
  • Fruity breath
  • Recurrent infections (thrush, cystitis and skin infections)

It is essential to note that the symptoms abovementioned aren’t necessarily a sign of high blood glucose, however, it is important that you see your GP to assess the cause of such symptoms.

What are the causes of high blood sugar?

If you have diabetes, you may experience increased levels of blood sugar due to the following triggers:

  • Stress
  • Overeating
  • Illnesses
  • Lack of exercise
  • Medication side effects
  • Steroids
  • Overtreatment of low blood sugar (hypoglycaemia)
  • Incorrect diabetes medicine dosage or a missed dose
  • Dawn phenomenon (surge of hormone production in the early morning hours)

Prediabetes however does not usually present any signs or symptoms. Therefore, it is particularly important to get tested if you are at an increased risk of developing diabetes due to:

  • Being overweight
  • Being over 45 years old
  • Doing little to no exercising
  • Having high blood pressure and/or high triglycerides levels
  • Having low ‘good’ cholesterol levels (HDL)
  • Having a history of insulin resistance, strokes and/or hypertension
  • Having a family history of diabetes
  • Having had diabetes in pregnancy

How to prevent and treat high blood sugar


If you have been diagnosed with diabetes, it is important that you keep monitoring and controlling your blood sugar levels. You can prevent surges in blood sugar by:

  • Adjusting your diet: avoid sugary foods and drinks, and be mindful of the way carbohydrates affect your blood sugar levels. Also, avoid snacking and overeating.
  • Drinking plenty of water, particularly if you are dehydrated.
  • Exercising regularly can help prevent your blood glucose levels from rising.
  • Adjusting your insulin dosage in line with your GP’s advice. Your levels can be monitored and adjusted to match your food and drink intake as best as possible.
  • Do not smoke
  • Limit your alcohol intake


Diabetes cannot be treated but the symptoms, including high blood glucose symptoms, can be monitored and controlled with insulin injections. The amount of insulin injected will typically depend on food intake and the amount of sugar and carbohydrates contained in each meal.

You may also need to test your blood or urine for ketones diabetic ketoacidosis (body running out of insulin).

How can I get tested for high blood sugar?

At a clinic

You can book a health check with one of our Certified Healthcare professionals at one of over 2,000 mobile clinics nationwide. All of our Health MOT Packages include a blood sugar test, in addition to a wide array of health markers for a detailed view of your health. You can choose between 3 levels of testing to suit your own personal needs.

At Home

Alternatively, you can get your blood sugar tested from the comfort of your own home with a single blood sugar home test kit. All you need to do is order your kit, take your own sample, send it back in our pre-addressed return envelope, and wait to receive your results online within 8 days.