Hyperglycaemia is glucose above your target. A single high reading after a large meal is ordinary. A pattern of highs, or a very high reading that will not come down, is information you should act on.
How it feels
Thirst, frequent urination, tiredness, blurred vision, headache, difficulty concentrating. Sustained highs also slow wound healing and make infections — skin, urinary, oral thrush — more likely and more stubborn.
Common causes
- More carbohydrate than the dose covered
- A missed or mistimed medication dose
- Illness or infection — even a simple cold raises glucose substantially
- Stress, poor sleep, pain
- Steroids and some other medications
- Insulin that has expired, been frozen, or sat in the heat and lost potency
- An injection site that has become lumpy from overuse, so absorption is erratic
- The dawn phenomenon — a normal early-morning hormone surge that raises glucose before you wake
Sick day rules
Illness raises glucose even when you are eating less, because stress hormones push the liver to release glucose. The instinct to reduce insulin because you are not eating is usually wrong and occasionally dangerous.
- Never stop your basal insulin. Your body needs it whether or not you are eating.
- Test more often — every three to four hours, including overnight.
- If you use insulin and are unwell, check ketones whenever glucose is above 240 mg/dL (13.3 mmol/L).
- Keep drinking. Sugar-free fluids if glucose is high, glucose-containing fluids if you cannot eat and glucose is falling.
- Ask your doctor in advance for a written sick-day plan with your own correction doses. Getting one during an illness is much harder.
Diabetic ketoacidosis
Without enough insulin, cells cannot use glucose and the body burns fat instead, producing ketones. Ketones are acidic; enough of them make the blood dangerously acidic. DKA is a medical emergency and develops over hours, not days. It is most associated with type 1 but does occur in type 2, particularly during severe illness and with SGLT2 inhibitor medications — where it can occur at surprisingly normal glucose levels.
Go to hospital now if you have: nausea or vomiting that will not stop · abdominal pain · deep, rapid, sighing breathing · breath that smells fruity or of acetone · moderate or large ketones · drowsiness or confusion · glucose that stays above 300 mg/dL (16.7 mmol/L) despite correction doses. Do not wait to see if it improves overnight.
The other emergency: HHS
Hyperosmolar hyperglycaemic state occurs mainly in older adults with type 2. Glucose rises extremely high — often above 600 mg/dL (33 mmol/L) — with severe dehydration but little or no ketone production. It builds over days and presents with profound thirst, weakness, and progressive confusion. It also requires emergency care.
Correcting a high safely
If your care team has given you a correction factor, use it — Sukkari's bolus estimator will do the arithmetic. Then wait. Rapid insulin takes three to five hours to finish working, and stacking a second dose after ninety minutes because the number has not moved enough is one of the most common routes to a bad low. Drink water, walk if you feel well, and re-check in two hours.