High blood glucose levels, also known as hyperglycaemia, is generally regarded as 15mmol/L or higher. People with diabetes will often experience high blood glucose levels (BGLs). If it is short lasting and you have type 2 diabetes it is not a great concern. If it continues over a few days, or blood glucose levels get higher and higher, then see your GP for advice. There may be an underlying illness that needs to be treated.

If you have type 1 diabetes you need to be a little more cautious as you risk ketones developing if your blood glucose levels are too high. It is recommended to keep your glucose in your target range.

What is a high blood glucosel level?

A high blood glucose level, also known as hyperglycaemia, is generally described as a blood glucose level of 15mmol/L or higher; well above general targets.

What causes high blood glucose levels?

Glucose levels vary all of the time, this is a normal part of how your body processes glucose. Some common causes for higher blood glucose levels over a period of time include:

• Increased stress
• Feeling unwell
• Chronic pain
• Missing/wrong medications or an incorrect dose
• Eating more than the recommended amount, or the wrong types, of carbohydrates
• Being less active
• Some medications, such as steroids
• Putting on weight, or carrying extra fat, particularly around your middle (this increases insulin resistance)

It is important to be prepared and have a sick day management plan to follow if you have hyperglycaemia and/or are unwell. Your GP, endocrinologist, or diabetes educator can help you to create a personal sick day plan.

Type 1 diabetes and high BGLs can be serious

If you have type 1 diabetes, blood glucose levels above 15mmol/L can be very serious. Your body will try to get energy from fat stores and as a result produce ketones, which in large amounts are toxic. Don’t wait for symptoms! Try and work out the cause/s, and bring your blood glucose levels back into range. Talk to your doctor or diabetes educator for advice and have a sick day plan ready. If your blood glucose levels are higher than 15mmol/L for six hours or more, you have elevated ketones, and/or you feel unwell, start your sick day plan. This fact sheet explains, when to follow them, what to include, tips on staying well and when to seek urgent medical help.

Type 2 diabetes and blood glucose levels

Type 2 diabetes is a progressive condition. This means that your blood glucose levels are likely to increase over time. Regular monitoring is needed. Again, illness may cause an increase in your blood glucose levels. If you have acute elevations over 15mmol/L for 8-12 hours, or are unwell, follow your sick day plan.

Symptoms of high blood glucose levels

Regardless of diabetes type, you may, or may not, feel signs or symptoms of hyperglycaemia such as being tired or lethargic, thirsty, passing large amounts of urine, developing a headache, blurred vision or nausea. If you are not able to figure out the cause, see your doctor or diabetes team. Regular reviews with your doctor and diabetes team will help you to manage your blood glucose levels and avoid, or prevent, the unwanted effects from diabetes.