Hyperglycaemia (high blood sugar)

Hyperglycaemia, or high blood sugar, can affect people with type 1 diabetes and type 2 diabetes. It can also affect pregnant women who have gestational diabetes.

Now and then it affects people who don't have diabetes, but this is usually only when they are seriously ill. For example, someone who has recently had a stroke or heart attack, or who has a severe infection.

Don't confuse hyperglycaemia with hypoglycaemia, which is when a person's blood sugar level drops too low.

What follows focuses on hyperglycaemia in people with diabetes.

The aim of diabetes treatment is to keep your blood sugar as close to normal as possible. But if you have diabetes, however careful you are, you're likely to have hyperglycaemia at some point.

You should know how to recognise and treat hyperglycaemia (high blood sugar), because it can lead to serious health problems if it's left untreated.

Occasional mild episodes usually aren't a cause for concern. They can be treated quite easily, or your blood sugar may return to normal on its own. But hyperglycaemia can be dangerous if blood sugar levels get very high or stay high for long periods.

Very high blood sugar can cause life-threatening complications, such as:

• diabetic ketoacidosis (DKA), a condition caused by the body needing to break down fat as a source of energy, which can lead to a diabetic coma. This tends to affect people with type 1 diabetes
• hyperosmolar hyperglycaemic state (HHS), which is severe dehydration caused by the body trying to get rid of excess sugar. This tends to affect people with type 2 diabetes

If your blood sugar is often high for long periods (over months or years), it can cause permanent damage to parts of the body such as the eyes, nerves, kidneys and blood vessels.

If you have hyperglycaemia regularly, speak to your doctor or diabetes care team. You may need to change your treatment or lifestyle to keep your blood sugar within a healthy range.

In people with diabetes, the symptoms of hyperglycaemia usually come on slowly, over a few days or weeks. Sometimes there are no symptoms at all until the blood sugar level is very high.

The symptoms include:

• increased thirst and a dry mouth
• needing to pee frequently
• tiredness
• blurred vision
• unintentional weight loss
• recurrent infections, such as thrush, bladder infections (cystitis) and skin infections

These symptoms can also be a sign of undiagnosed diabetes. If this applies to you, see your doctor, who can arrange a test to check for the condition.

When you're first diagnosed with diabetes, your diabetes care team will usually tell you what your blood sugar level is and what you should aim to bring it down to.

You may be advised to use a testing device to check your blood sugar regularly at home. Or you may see a nurse or doctor every few months to find out what your level is.

Target blood sugar levels differ from person to person, but generally speaking:

• if you check your own blood sugar at home, a normal target is 4-7mmol/l before eating and under 8.5-9mmol/l two hours after a meal
• if you're tested every few months, a normal target is below 48mmol/mol (or 6.5% on the older measurement scale)

Several things can push up the blood sugar level in people with diabetes, including:

• stress
• an illness, such as a cold
• eating too much, such as snacking between meals
• a lack of exercise
• dehydration
• missing a dose of your diabetes medicine, or taking an incorrect dose
• over-treating an episode of hypoglycaemia (low blood sugar)
• taking certain medicines, such as steroid medicine

Children and young adults can also have occasional episodes of hyperglycaemia during growth spurts.

If you've been diagnosed with diabetes and you have symptoms of hyperglycaemia, follow the advice your care team has given you to bring your blood sugar level down. If you're not sure what to do, contact your doctor or care team.

You may be advised to:

• change your diet, for example by avoiding foods that make your blood sugar levels rise, such as cakes or sugary drinks
• drink plenty of sugar-free fluids, which can help if you're dehydrated
• exercise more often, because gentle, regular exercise such as walking can often lower your blood sugar level, particularly if it helps you lose weight
• adjust your dose, if you use insulin (your care team can give you specific advice about how to do this)

You may also be advised to monitor your blood sugar level more closely, or to test your blood or urine for substances called ketones (associated with diabetic ketoacidosis).

Until your blood sugar level is back under control, watch out for additional symptoms that could be a sign of a more serious condition (see below).

Contact your diabetes care team straight away if your blood sugar level is high and you also have any of these symptoms:

• feeling or being sick
• abdominal (tummy) pain
• rapid, deep breathing
• signs of dehydration, such as a headache, dry skin and a weak, rapid heartbeat
• difficulty staying awake

These symptoms could point to diabetic ketoacidosis or a hyperosmolar hyperglycaemic state (see above), and you may need to be looked after in hospital.

There are some simple ways to lower your risk of severe or prolonged hyperglycaemia:

• Be careful what you eat. Pay particular attention to how snacking and eating sugary foods or carbohydrates can affect your blood sugar level.
• Stick to your treatment plan. Remember to take your insulin or other diabetes medicines as recommended by your care team.
• Be as active as you can. Regular exercise can help stop your blood sugar level rising, but check with your doctor first if you're taking diabetes medicine, because some medicines can lead to hypoglycaemia if you exercise too much.
• Take extra care when you're ill. Your care team can give you some "sick day rules" that set out what you can do to keep your blood sugar level under control during an illness.
• Monitor your blood sugar level. Your care team may suggest a device to check your level at home, so you can spot a rise early and take steps to stop it.