Hyperglycaemia (high blood sugar): symptoms, causes and what to do

The NHS says symptoms of high blood sugar usually come on gradually and may only start when your blood sugar level gets very high. That is one reason people can have raised glucose for a long time without realising.

Because the pattern overlaps with undiagnosed diabetes, the NHS advises seeing your care team or GP surgery if you have symptoms of high blood sugar and have not been diagnosed with diabetes.

• Feeling very thirsty.

• Peeing a lot.

• Feeling weak or tired.

• Blurred vision.

• Losing weight.

• For type 2 diabetes the NHS also lists cuts or wounds taking longer to heal, and itching around the penis or vagina or recurring thrush.

Hyperglycaemia is the medical word for blood sugar that is too high. Sugar (glucose) comes from food and drink and is the body's main fuel. In diabetes there is either not enough insulin, or the insulin does not work as it should, so glucose builds up in the blood.

The NHS gives the figures below as a guide for people who already have diabetes. It stresses that your own targets may differ with your age and the type of diabetes you have, so check what your doctor or care team has agreed with you.

For most people with diabetes the answer is to deal with the reason it rose and to follow the plan their care team has given them. The NHS lists what helps, and also what to avoid.

The NHS says to speak to your care team or GP surgery if you have tried to lower your blood sugar but it is still high or you still have symptoms. If your insulin is not bringing a high reading down, the NHS diabetic ketoacidosis page says to call your diabetes care team now or get help from NHS 111.

• Take any diabetes medicine you have been prescribed, as advised by your doctor or care team.

• Avoid eating too much sugary or starchy food.

• Find ways to manage stress.

• Exercise regularly and lose weight if you are overweight.

• Follow your care team's advice about what to do while you are ill, sometimes called sick day rules.

• Do not skip or change doses of your diabetes medicine unless your doctor or care team advises it.

The NHS names a set of everyday triggers in people with diabetes: being unwell, feeling stressed, eating too much sugary or starchy food, being less active than usual and missing doses of diabetes medicine.

It also says blood sugar can be high if your diabetes medicine is not working well, if you are taking certain medicines such as steroids, or if you recently had an operation. If the cause is not obvious, or the readings keep climbing, that is a reason to contact your care team rather than wait.

Diabetic ketoacidosis (DKA) happens when a lack of insulin causes harmful substances called ketones to build up in the blood. The NHS says it can be life threatening and needs urgent treatment in hospital. It usually affects people with type 1 diabetes, but can also happen in people with type 2 diabetes who need insulin, and can be how type 1 first shows itself, particularly in children.

If you have diabetes and your blood sugar is high, the NHS advises testing for ketones if you can. The NHS says these ketone levels are a guide, and your diabetes team will tell you which levels to act on.

The NHS says to call 999 or go to A&E if you think you have high blood sugar and you have any of the signs below. These could be signs you are becoming seriously unwell. The NHS also says not to drive yourself to A&E: ask someone to drive you or call 999, and bring your medicines.

• Feeling sick, being sick or having stomach pain.

• Breathing more quickly than usual, or a faster heartbeat.

• Feeling drowsy or struggling to stay awake.

• Breath that smells fruity, like pear drop sweets.

• Confusion or difficulty concentrating.

• A high level of ketones in your blood or pee (over 3 mmol/L in blood, or over 2+ in pee).

• Symptoms of DKA when you have not been diagnosed with diabetes.

The NHS says it is not usually a serious problem if your blood sugar is sometimes slightly high for a short time. The risk comes when it stays high for a long time or reaches a very high level.

Over time, the NHS says this can cause permanent damage to the nerves in your hands and feet (peripheral neuropathy), permanent damage to your eyes and problems with your sight (diabetic retinopathy), heart disease and stroke, and life-threatening conditions such as diabetic ketoacidosis.

On the NHS, high blood sugar is usually followed up through your GP surgery and diabetes care team, using HbA1c and glucose tests and, where relevant, ketone testing. The NHS says you can get ketone testing kit free from the NHS or buy it from a pharmacy.

Private clinics can also arrange blood glucose and HbA1c testing and specialist diabetes review, usually on a self-paid basis. Treatment plans and targets should still be agreed with the team that looks after your diabetes, and sudden severe symptoms should always go to emergency care.