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What to do if…
your blood sugar reading is suddenly very high and you feel sick

Short answer

Treat this as urgent: check for ketones (if you can) and get same-day medical advice now. If you have signs of diabetic ketoacidosis (DKA) or you cannot safely manage at home, call 999 or go to A&E.

Do not do these things

  • Do not try to “exercise it down” when you feel sick or if ketones might be present.
  • Do not take extra insulin in a new/guessed dose if you do not have a sick-day/correction plan you’ve already been given.
  • Do not stop your insulin (especially long-acting/basal) unless a clinician tells you to.
  • Do not ignore repeated vomiting, severe drowsiness/confusion, or breathing that becomes deep/rapid.
  • Do not drink sugary drinks to “pick yourself up” unless you’re treating low blood sugar.
  • Do not keep taking an SGLT2 inhibitor if you are vomiting/dehydrated or have possible DKA symptoms without getting urgent medical advice (these medicines have specific “sick day” rules for many people).
  • Do not drive yourself to urgent care if you feel faint, confused, very sleepy, or your vision is blurred.

What to do now

  1. Check for “call 999 now” red flags. Call 999 (or go to A&E) if any of these apply:
    • You have high ketones (commonly: blood ketones over 3 mmol/L, or urine ketones over 2+).
    • You do not know your ketone level but have DKA-type symptoms (very thirsty/peeing a lot, sleepy or confused, breath that smells fruity, deep/rapid breathing, vomiting).
    • You can’t keep fluids down, you’re getting more drowsy, or you’re getting confused.
  2. Re-check the reading to rule out a bad test. Wash and dry hands, use a fresh strip, and re-test. If you use a CGM, confirm with a fingerstick if the number doesn’t match how you feel.
  3. Check ketones as soon as possible (especially if type 1, pregnant, or on an SGLT2 inhibitor).
    • Test ketones if you’re unwell, and especially if your glucose is above your target range (for many people with type 1 this is often around/above 14 mmol/L, but follow your own plan if different).
    • If ketones are present or rising, get urgent clinical advice the same day.
  4. Follow your personal “sick day” plan exactly (if you have one).
    • Take insulin/diabetes medicines as prescribed, including any clinician-written correction guidance for illness.
    • If you use an insulin pump and sugars are unexpectedly high: check the pump is delivering, check the cannula/infusion set and site, and follow your pump sick-day instructions. If you don’t have a clear backup plan and you suspect delivery failure, get urgent advice rather than improvising.
  5. Start small, steady fluids. Sip sugar-free fluids regularly (water is fine). If you’re vomiting, try very small sips frequently. If you cannot keep fluids down, treat that as urgent and seek medical help.
  6. Get urgent help if you’re unsure, alone, or not improving.
    • If it’s not an emergency but you need urgent advice: use NHS 111 (in Scotland, this reaches NHS 24). In Northern Ireland, use your GP out-of-hours service for urgent medical advice when your GP practice is closed.
    • If you are worsening or have any red flags (Step 1): 999 / A&E.
  7. If you take an SGLT2 inhibitor and you feel very unwell, act early. If you have nausea/vomiting, abdominal pain, deep/rapid breathing, unusual sleepiness, or you’re dehydrated, seek urgent assessment (and mention you take an SGLT2 inhibitor), because ketones can be a concern even when glucose isn’t extremely high.
  8. Keep a simple record for clinicians. Note the times and results of glucose/ketones, any vomiting/fever, and what medication you’ve taken.
  9. Have someone stay with you if possible. Ask a friend/family member to check in. If you must go to hospital, bring your diabetes meds, devices, and test supplies if you can do so safely.

What can wait

  • You do not need to work out the exact cause right now (food, stress, infection, missed dose) — focus on safety and getting help.
  • You do not need to make long-term medication changes today.
  • You do not need to “push through” normal activities; resting and monitoring is enough until you’re stable and advised.

Important reassurance

Feeling sick with a very high reading is frightening, and it’s reasonable to treat it as urgent. Getting ketones checked and getting help early is a protective step that can prevent serious complications.

Scope note

These are first steps for the next few hours to reduce immediate risk. Ongoing management (dose changes, infection work-up, medication review) should be done with your diabetes clinician.

Important note

This guide is general information, not medical advice. High blood sugar with illness can become an emergency quickly (including DKA or hyperosmolar hyperglycaemic state). If you’re worsening, pregnant, on an SGLT2 inhibitor, can’t check ketones, or you’re unsure what to do next, err on the side of urgent medical assessment.

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