High blood sugar (hyperglycaemia) is where the level of sugar in your blood is too high. It mainly affects people with diabetes and can be serious if not treated. People with diabetes can also have blood sugar that's too low. This is called low blood sugar (hypoglycaemia). If you have diabetes, you can find out if your blood sugar level is high by having a blood sugar (blood glucose) test. You may have regular tests by your care team or GP surgery, or you may have tests you can do at home.
Types of diabetes test and high blood sugar levels.High
blood sugar levels
Type of testHigh level Test done by a health professional to check your blood sugar level over the last 2 or 3 months (HbA1c test)
48 mmol/mol or over (6.5% if you're given a percentage)
Test done by a health professional after not eating for a few hours (fasting glucose test)
Over 7 mmol/L
Home test done after waking up or before eating
Over 7 mmol/L
Home test done at any other time
Over 11 mmol/L
Important: Important
These blood sugar levels are a guide. Your levels may be different depending on your age and the type of diabetes you have. Check with your doctor or care team.
Symptoms of high blood sugar
Symptoms of high blood sugar usually come on gradually and may only start when your blood sugar level gets very high.
Common symptoms include:
- feeling very thirsty
- peeing a lot
- feeling weak or tired
- blurred vision
- losing weight
Causes of high blood sugar
Common causes of high blood sugar in people with diabetes include:
- being unwell
- feeling stressed
- eating too much sugary or starchy food
- being less active than usual
- missing doses of diabetes medicine
You can also get high blood sugar if your diabetes medicine is not working well, you're taking certain medicines (such as steroids) or you recently had an operation.
How to lower your blood sugar
If you have diabetes, it's important to try to stop your blood sugar level getting too high.
Do
take any diabetes medicine you've been prescribed, as advised by your doctor or care team
avoid eating too much sugary or starchy food
try to find ways to manage stress
exercise regularly
lose weight if you're overweight
follow advice from your doctor or care team about what to do while you're ill (sometimes called "sick day rules")
Don’t
do not skip or change doses of your diabetes medicine unless advised by your doctor or care team
Non-urgent advice: Speak to your care team or GP surgery if:
- you've tried to lower your blood sugar but your blood sugar level is still high or you still have symptoms
- you have symptoms of high blood sugar and you have not been diagnosed with diabetes
Problems caused by high blood sugar
It's not usually a serious problem if your blood sugar is sometimes slightly high for a short time.
But high blood sugar can cause serious problems if it stays high for a long time or gets to a very high level.
It can lead to:
- permanent damage to the nerves in your hands and feet (peripheral neuropathy)
- permanent damage to your eyes and problems with your sight (diabetic retinopathy)
- life-threatening conditions such as diabetic ketoacidosis
If you have high blood sugar, your doctor or care team may ask you to test your blood or pee to check for ketones. A high level of ketones is a sign of diabetic ketoacidosis.
Urgent advice: Call your care team immediately or get help from NHS 111 if:
You think you have high blood sugar and:
- you're feeling sick, being sick or have stomach pain
- you're breathing more quickly than usual or your heart is beating faster than usual
- you feel drowsy or are struggling to stay awake
- your breath has a fruity smell (like pear drop sweets)
- you feel confused or have difficulty concentrating
- you have a high level of ketones in your blood or pee
These could be signs you're becoming seriously unwell.
You can call 111 or get help from 111 online.
Page last reviewed: 26 May 2022
Next review due: 26 May 2025
Blood sugar control is at the center of any diabetes treatment plan. High blood sugar, or hyperglycemia, is a major concern, and can affect people with both type 1 and type 2 diabetes . There are two main
kinds: Frequent or ongoing high blood sugar can cause damage to your nerves,
blood vessels, and organs. It can also lead to other serious conditions. People with type 1 diabetes are prone to a build-up of acids in the blood called ketoacidosis. If you have
type 2 diabetes or if you’re at risk for it, extremely high blood sugar can lead to a potentially deadly condition in which your body can’t process sugar. It's called hyperglycemic hyperosmolar nonketotic syndrome (HHNS). You’ll pee more often at first, and then less often later on, but your urine may become dark and you could get severely dehydrated. It's
important to treat symptoms of high blood sugar right away to help prevent complications. Your blood sugar may rise if you: Early signs include: Ongoing high blood sugar may cause: High Blood Sugar and Diabetes
Causes
Symptoms
If you have diabetes and notice any of the early signs of high blood sugar, test your blood sugar and call the doctor. They may ask you for the results of several readings. They could recommend the following changes: Drink more water. Water helps remove excess sugar from
your blood through urine, and it helps you avoid dehydration. Exercise more. Working out can help lower your blood sugar. But under certain conditions, it can make blood sugar go even higher. Ask your doctor what kind of exercise is right for you. Caution: If you have
type 1 diabetes and your blood sugar is high, you need to check your urine for ketones. When you have ketones, do NOT exercise. If you have type 2 diabetes and your blood sugar is high, you must also be sure that you have no ketones in your urine and that you are
well-hydrated. Then your doctor might give you the OK to exercise with caution as long as you feel up to it. Change your eating habits. You may need to meet with a dietitian to change the amount and types of foods you eat. Switch medications. Your doctor may change the amount, timing, or type of diabetes medications you take. Don’t make changes without talking to
them first. If you have type 1 diabetes and your blood sugar is more than 250 mg/dL, your doctor may want you to test your urine or blood for ketones. Call your doctor if your blood sugar is running higher than your treatment goals. If you work
to keep your blood sugar under control -- follow your meal plan, exercise program, and medicine schedule -- you shouldn’t have to worry about hyperglycemia. You can also:How Is It Treated?
How to Prevent It