High Blood Sugar Symptoms: Early Signs, Ketones and When to Get Help

High blood sugar symptoms often start quietly. You may feel thirsty, tired or need the toilet more. The NHS says the "symptoms of high blood sugar usually come on gradually and may only start when your blood sugar level gets very high."^[1] This guide covers the early signs of high blood sugar, the numbers health services use, what to do if blood sugar is high and when to get help fast.

This guide is general education. If you use insulin or other glucose medicines, follow the plan your diabetes team gave you.

What are the symptoms of high blood sugar?

High blood sugar is also called hyperglycaemia (hyperglycemia in US spelling). The American Diabetes Association explains that it "happens when the body has too little insulin or when the body can't use insulin properly."^[5]

The NHS lists these common symptoms:^[1]

• Feeling very thirsty.
• Peeing a lot.
• Feeling weak or tired.
• Blurred vision.
• Losing weight.

The US National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) gives a similar list of hyperglycemia symptoms: "feeling tired", "feeling thirsty", "having blurry vision" and "urinating too often."^[6]

High blood sugar levels at a glance

Health services use slightly different numbers. Here is what each one says:

The NHS adds: "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."^[1]

What are the early signs of high blood sugar?

A small rise often has no signs at all. Diabetes UK says "if your blood sugar levels are slightly above your targets, there are usually no symptoms."^[7] It adds that "the blood sugar level at which symptoms start can be different for everyone. Common symptoms include needing to go for a wee more often, feeling very thirsty, feeling tired and having headaches."^[7]

Type 2 diabetes can go unnoticed for a long time. The NHS says "not everyone with type 2 diabetes has symptoms, so it's important to get checked out."^[8] It also lists "cuts or wounds taking longer to heal" and "itching around your penis or vagina, or you keep getting thrush" as possible signs.^[8]

What should you do if your blood sugar is high?

One high reading is not always a worry. The NHS says "it's not usually a serious problem if your blood sugar is sometimes slightly high for a short time."^[1] It lists common causes:^[1]

• Being unwell.
• Feeling stressed.
• Eating too much sugary or starchy food.
• Being less active than usual.
• Missing doses of diabetes medicine.

Here is what to do if blood sugar is high:

1. Check again. Wash and dry your hands and test again to rule out a meter error.^[7]
2. Check ketones if your team has told you to. Diabetes UK says "if your blood sugar is high (usually above 13), or you feel very unwell, check for ketones." That is 13 mmol/L, or about 234 mg/dL.^[9]
3. Follow your sick day rules. If you use insulin or tablets, follow the plan your diabetes team gave you for days when you are ill.^[1][9]
4. Do not exercise with ketones. The ADA says "if your blood glucose is above 240 mg/dl, check your urine for ketones. If you have ketones, do not exercise." That is 240 mg/dL (13.3 mmol/L).^[5]
5. Call your team if it stays high. The NHS advises speaking to your care team or GP surgery if your level is still high or you still have symptoms.^[1]

The numbers for checking ketones differ between sources. Diabetes UK uses "usually above 13" mmol/L.^[9] The ADA patient page uses 240 mg/dL (13.3 mmol/L), in its advice on exercise.^[5] The CDC says to check your urine for ketones if you are sick or your blood sugar is 250 mg/dL (13.9 mmol/L) or above.^[2] The ADA Standards of Care, written for doctors, say people at risk of diabetic ketoacidosis should measure ketones "particularly if glucose levels exceed 200 mg/dL (11.1 mmol/L)."^[10] Use the number your own team gave you.

Writing down your high blood sugar symptoms

A short note each time can help your team spot a pattern:

• The reading and the time.
• How you felt.
• What you ate, and any missed dose.
• Whether you were ill or stressed.
• Your ketone result, if you checked.

Never take extra insulin or an extra sulfonylurea tablet such as gliclazide or glimepiride to bring a high reading down unless your diabetes team's plan tells you how to do so, as this can cause low blood sugar (a hypo).^[1][11] Low blood sugar usually means below 4 mmol/L (72 mg/dL) in the UK or below 70 mg/dL (3.9 mmol/L) in the US.^[11][12] Our guide to low blood sugar covers the warning signs. In the UK, the NHS says to call 999 if someone may have very low blood sugar and is not responding normally or is unconscious, and a glucagon injection is not available or you do not know how to use it, or they have not recovered within 10 minutes of a glucagon injection, or they have been drinking alcohol.^[11] In the US, the ADA says to call 911 right away if someone is unconscious and glucagon is not available or no one knows how to use it.^[12]

Can you have high blood sugar without diabetes?

Yes. The ADA notes that "recent physical activity, illness, or acute stress can affect glucose concentrations."^[13] In hospital care, the ADA lists stress hyperglycemia and drug-related hyperglycemia as their own types.^[4] It says steroid medicines "can induce hyperglycemia" in 56% to 86% of hospital patients who take them, with or without diabetes.^[4] The NHS adds that you can get high blood sugar if "you're taking certain medicines (such as steroids) or you recently had an operation."^[1]

Prediabetes is the stage before type 2. The NHS describes it as blood glucose levels that "are higher than normal but not high enough for you to be diagnosed with diabetes."^[8] The NIDDK says "people with insulin resistance and prediabetes usually have no symptoms."^[14] It defines prediabetes as an HbA1c of 5.7% to 6.4% (39 to 47 mmol/mol) or a fasting glucose of 100 to 125 mg/dL (5.6 to 6.9 mmol/L).^[14] It also says "in 2021, about 97.6 million people in the United States ages 18 and older had prediabetes."^[14]

If you have symptoms of high blood sugar and no diagnosis, the NHS advises you to speak to your GP surgery.^[1] In someone with no diagnosis, high blood sugar can also be the first sign of type 1. The NHS says diabetic ketoacidosis "can happen when people first develop type 1 diabetes and have not yet been diagnosed, particularly children."^[3] The NHS says call 999 or go to A&E if you have symptoms of diabetic ketoacidosis and have not been diagnosed with diabetes.^[3]

When is high blood sugar an emergency?

Very high blood sugar can lead to two serious conditions. The NIDDK says it "may lead to confusion or fainting, and it may become a serious medical emergency."^[6]

Diabetic ketoacidosis (DKA)

DKA happens when the body runs short of insulin and makes ketones. The NHS lists these symptoms:^[3]

• Feeling thirsty and needing to pee more often.
• Stomach pain, feeling sick or being sick.
• Diarrhoea.
• Breathing more deeply than usual.
• Breath that smells fruity, like pear drop sweets or nail polish remover.
• Feeling tired, sleepy or confused.
• Blurred vision.

The NHS says "the symptoms usually develop over 24 hours, but it can be faster."^[3] Diabetes UK says they can come on faster "especially in children or if you use an insulin pump."^[9] The NIDDK notes that DKA most often affects people with type 1, but "some people with type 2 diabetes can develop ketoacidosis if they do not produce enough insulin."^[6] A normal glucose reading does not fully rule it out. The ADA says "approximately 10% of people experiencing DKA present with euglycemic DKA (plasma glucose <200 mg/dL [<11.1 mmol/L])."^[4]

The NHS uses these blood ketone bands:^[3]

For urine strips, the NHS says "over 2+ is high."^[3] It adds that "these ketone levels are a guide. Normal blood ketone levels can be different for different people."^[3]

Hyperosmolar hyperglycaemic state (HHS)

HHS happens in people with type 2 diabetes, including type 2 that has not been diagnosed yet.^[15] Diabetes UK calls it "a potentially life-threatening emergency" and says it "can develop over many days."^[15] By the time it is found, "your blood sugar levels can often be over 40mmol/l" (720 mg/dL).^[15] Its symptoms include peeing more often, "feeling very thirsty all the time", "very dry skin" and "confusion and, in later stages, feeling sleepy and a gradual loss of consciousness."^[15] Diabetes UK warns that "some people who are developing HHS put symptoms down to other things and may take longer to seek help."^[15]

A 2024 consensus report from several diabetes societies says DKA can develop over "hours to a few days," while HHS "may take days or weeks to develop."^[16] It lists infection and "the omission of insulin therapy" as the most frequent triggers.^[16] Several authors report NIH or other research grants and ties with drug and device companies, including Dexcom, Novo Nordisk and Sanofi.^[16]

Who to call

In the UK, the NHS says call 999 or go to A&E if you think you have high blood sugar and:^[1]

• "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"

"Do not drive to A&E. Ask someone to drive you or call 999 and ask for an ambulance."^[1] If you have diabetes and your ketones are 1.6 to 3 mmol/L, or your glucose stays high after your insulin, the NHS says call your diabetes care team now or NHS 111.^[3]

In the US, the CDC says "go to the emergency room or call 911 right away" if your blood sugar "stays at 300 mg/dL or above" (16.7 mmol/L), your breath smells fruity, you are vomiting and "can't keep food or drinks down," you have trouble breathing or you have several signs of DKA.^[2]

Elsewhere, call your local emergency number.

Questions to ask your diabetes team

• What blood glucose level should make me call you?^[1][6]
• Should I have a blood ketone meter, and at what reading should I use it?^[3][9][10]
• What are my sick day rules for my insulin or diabetes tablets?^[1][9]
• Am I at risk of DKA or HHS? The ADA asks teams to review this at every visit for people at risk.^[10]

Frequently asked questions

What blood sugar level is too high?

The NHS calls over 7 mmol/L (126 mg/dL) high on waking or before eating, and over 11 mmol/L (198 mg/dL) at least 90 minutes after eating.^[1] The NIDDK says above 180 mg/dL (10.0 mmol/L) is too high for most people with diabetes.^[6] Your own targets may differ.^[1]

What does high blood sugar feel like?

Common symptoms are thirst, peeing a lot, tiredness, blurred vision and headaches.^[1][7] A small rise often causes no symptoms at all.^[7]

Can stress cause high blood sugar?

Yes. The NHS lists feeling stressed among the causes of high blood sugar,^[1] and the ADA says acute stress and illness can affect glucose.^[13]

When should I go to A&E with high blood sugar?

The NHS says call 999 or go to A&E if you have high blood sugar and are being sick, breathing fast, drowsy, confused, have fruity breath or have high ketones.^[1] In the US the CDC says call 911 if your blood sugar stays at 300 mg/dL (16.7 mmol/L) or above, your breath smells fruity, you cannot keep food or drinks down or you have trouble breathing.^[2]

Where to go next

High blood sugar symptoms are easy to miss at first, and these guides explain how to track your readings and act early:

• Checking your glucose, for tracking your own readings.
• Low blood sugar, for the signs of a hypo and what to do.
• Is Diabec legit?, for what is in our supplement and what it does not do.

Note: If you are pregnant, breastfeeding, or considering giving any supplement or herbal product to a child, consult your healthcare provider before making any changes to your diet, supplement routine, or prescribed medications.