High blood sugar: signs, causes and what to do

High blood sugar, or hyperglycaemia to use the technical term, occurs when you have too much glucose in your blood. Persistently high blood glucose levels can cause health complications, including damage to the nerves, eyes, heart and kidneys. Knowing the warning signs of high blood sugar can help you catch it early and take corrective action.

You can have high blood sugar (hyperglycaemia) without having diabetes, although it is more commonly discussed in people living with diabetes.^1,2 Glucose levels do naturally fluctuate, and that may be caused by:

• Prediabetes, when blood sugar is elevated but not high enough to be classified as type 2 diabetes
• Stress and illness can trigger stress-induced hyperglycaemia as your body releases cortisol and adrenaline
• Medications, including corticosteroids, immunosuppressants, and some blood pressure medications
• Other medical conditions that affect insulin production, such as polyendocrine metabolic ovarian syndrome (PMOS), Cushing’s syndrome, and pancreatic disease
• Lifestyle factors such as poor sleep, dehydration, missing meals, or a diet high in refined carbohydrates

Occasional episodes of hyperglycaemia can also occur in children and young adults during growth spurts. If you experience symptoms of high blood sugar (see below) and do not have diabetes, consult your doctor, who will help to determine the cause.

In type 1 diabetes, symptoms often come on suddenly and are notable enough to warrant a prompt diagnosis. In type 2 diabetes, symptoms of hyperglycaemia often develop slowly. Some people have few to no symptoms, while others write off warning signs as part of the ageing process. Here are some of the key signs that your blood sugar levels may be elevated.^2,3

Extreme tiredness: if your body is struggling to convert sugar into energy, you may feel exhaustion known as diabetic fatigue.

Frequent urination and excessive thirst: a process called osmotic diuresis triggers a cycle of dehydration and increased thirst.

Blurred vision: excess glucose in your bloodstream pulls fluid into the eye, affecting its ability to focus.

Weight loss: when your body can’t use the glucose for fuel, it will turn to fat and muscle instead.

Difficulty concentrating and mood swings: When energy delivery to the brain is disrupted, this can lead to ‘brain fog’, as well as irritability and anxiety.

Infections and slow-healing wounds: high blood sugar can make your immune system sluggish so it can’t fight bacteria. You may find cuts and burns take a long time to heal.

If you’ve been diagnosed with diabetes and you have symptoms of hyperglycaemia, your care team will have given you personalised advice on how to reduce your blood sugar level.⁴ You may be advised to:

• change your diet, for example, cutting out sugary foods and drinks
• drink plenty of sugar-free fluids if you are dehydrated
• exercise more often, gentle, regular exercise such as walking can often lower your blood sugar level, particularly if it helps you lose weight
• Adjust your insulin dose
• Monitor your blood sugar level or test your blood or urine for ketones

If untreated, hyperglycaemia can cause a range of serious health issues and long-term complications, such as nerve, kidney and eye damage, and an increased risk of stroke and heart disease.^3,4

People living with diabetes are at risk of short-term complications. Diabetic ketoacidosis (DKA) is a potentially life-threatening condition, which is primarily a risk for people living with type 1 diabetes.

This happens because the body lacks enough insulin to use glucose for fuel. It is then forced to break down fat for energy, producing acids called ketones that can build to toxic levels in the blood.

Symptoms of ketoacidosis include:⁵

• Nausea and vomiting
• Breath that smells sweet or fruity
• Shortness of breath
• Confusion, extreme drowsiness, disorientation or loss of consciousness

Note: Ketoacidosis is vastly different from ketosis, which is a type of metabolic process. Ketoacidosis is a life-threatening medical emergency.

People with type 2 diabetes are at risk of hyperosmolar hyperglycaemic state, where extremely high blood sugar levels can cause severe dehydration and changes to mental state.⁵

Almost 1.3 million Australians are living with type 2 diabetes and up to 500,000 people may be living with silent, undiagnosed type 2 diabetes.⁶ If you delay medical assessment, by the time diabetes is diagnosed, complications may already have set in.⁷

Prompt treatment can help reduce the risk of long-term complications, including heart, kidney, nerve and eye problems. Early intervention may also increase the chance of type 2 diabetes remission for some people and reduce the risk of further complications.^3,7

If you haven’t been diagnosed with diabetes but are experiencing symptoms of high blood sugar, see your doctor for further investigation. If you have diabetes and suspect your levels are elevated, check your blood glucose if you have a glucose meter, follow the plan from your care team and seek urgent medical help if symptoms worsen.^1,4

Diabetes Australia has comprehensive information on all types of diabetes, including signs and symptoms.