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Highs and ketones

A hyper is high blood sugar. Most highs are managed over a few days, but a very high reading with ketones can become a medical emergency.

What a hyper is

A “hyper” is hyperglycaemia – high blood sugar. What counts as high varies from person to person, but readings that sit persistently above your target range matter. This app flags any reading of 15 mmol/L or over as very high, because that is the point where, with type 1 diabetes, you may need to check for ketones.

How a hyper feels

High blood sugar can come on slowly, so the signs are easy to miss. The common symptoms are:

  • feeling very thirsty
  • peeing more than usual
  • tiredness
  • headaches
  • blurred vision

What causes a high reading

A hyper usually has a reason behind it. Common causes include:

  • too little insulin or diabetes medicine
  • being unwell or stressed
  • eating more carbohydrate than usual
  • less activity than usual
  • some other medicines, such as steroids

What to do about a high reading

A single high reading is usually not an emergency – look for a pattern over a few days rather than reacting to one number. In the meantime:

  • drink plenty of sugar-free fluids to stay hydrated
  • follow any “sick-day rules” your diabetes team has given you
  • do not stop taking insulin without advice from your team
  • speak to your diabetes team if the highs keep happening

Spotting the pattern

One reading is a snapshot. Logging highs over days and weeks shows which times of day run high and whether a change is working. You can start logging free and bring a report to your next appointment to talk it through.

Where ketones come in

When there is not enough insulin, the body cannot use glucose for energy, so it starts to burn fat instead. Burning fat makes ketones. If ketones build up in the blood they turn it acidic and can cause diabetic ketoacidosis (DKA). This is mainly a risk for people with type 1 diabetes.

When to check for ketones

If you have type 1 diabetes, check your ketones when your blood sugar is high – around 15 mmol/L or more – and/or when you feel unwell. You can use a blood ketone meter or a urine ketone test.

What your ketone level means

These are the blood ketone levels the NHS uses as a guide:

Blood ketone levels in mmol/L and what to do
Blood ketonesWhat it means
0.6 to 1.5 mmol/LSlightly raised – test again in a couple of hours.
1.6 to 3 mmol/LYou are at risk of DKA – contact your diabetes care team or NHS 111 for advice.
Over 3 mmol/LCall 999 or go to A&E. (On a urine test, a reading of 2+ means the same.)

DKA is a medical emergency

Diabetic ketoacidosis can become life-threatening quickly. The warning signs are:

  • feeling or being sick
  • tummy (stomach) pain
  • breathing more deeply or quickly than usual
  • breath that smells fruity, like pear drops
  • feeling very drowsy or confused

Call 999 or go to A&E now

If you have any of these warning signs, especially together with ketones, call 999 or go to A&E straight away. Always go to A&E if you have any ketones and are being sick, have stomach pain, or are very drowsy. See what to do about a very high reading.

Most highs never get this far – they are managed with fluids, your usual medicine and your team's sick-day advice. Knowing the warning signs just means you can act fast on the rare occasion it matters.

Checked against NHS and NICE guidance on . See all official sources.