High blood sugar (hyperglycaemia)
Hyperglycaemia is a blood glucose level above normal. It can be a one-off finding on a blood test or an ongoing problem in someone with diabetes.
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Medicines commonly prescribed for High blood sugar (hyperglycaemia)
For informational purposes only. Always consult a doctor before using any medicine.
Dosage form: TABLET, 1000 mgActive substance: metforminManufacturer: Medochemie Iberia S.A.Prescription requiredDosage form: TABLET, 500 mgActive substance: metforminManufacturer: Medochemie Iberia S.A.Prescription requiredDosage form: TABLET, 850 mg / tabletActive substance: metforminManufacturer: Aurovitas Spain, S.A.U.Prescription required
Hyperglycaemia is a blood glucose level above normal. It can be a one-off finding on a blood test or an ongoing problem in someone with diabetes. Either way it deserves attention: in the short term, very high glucose can become an emergency, and over the long term it damages blood vessels, nerves, kidneys and eyes without producing any symptoms.
What counts as high
- fasting glucose: normal below 5.6 mmol/L; 5.6–6.9 mmol/L indicates prediabetes; 7.0 mmol/L or above on two occasions indicates diabetes;
- two hours after eating: normal below 7.8 mmol/L;
- HbA1c: normal below 42 mmol/mol (6.0%); 42–47 mmol/mol indicates prediabetes; 48 mmol/mol (6.5%) or above indicates diabetes;
- a single home glucose meter reading is not enough to diagnose anything: a laboratory test is needed.
Symptoms
With moderate elevations there are usually none, and that is the problem. By the time symptoms appear, glucose is already quite high.
- intense thirst and a dry mouth;
- passing urine often, including at night;
- tiredness and lack of energy;
- blurred vision;
- constant hunger;
- unintended weight loss;
- slow-healing wounds;
- repeated infections of skin, gums or genital thrush;
- itchy skin;
- tingling in the feet.
When urgent care is needed
- nausea and vomiting with abdominal pain;
- deep, rapid breathing;
- fruity or acetone-smelling breath;
- marked drowsiness, confusion, difficulty rousing;
- glucose above 17 mmol/L with feeling unwell;
- positive ketones in blood or urine;
- marked dehydration in an older person with very high glucose.
These point to diabetic ketoacidosis or a hyperosmolar state, both genuine emergencies requiring hospital care.
Why glucose rises
In people with diabetes
- a missed dose of medication or insulin;
- a meal with more carbohydrate than expected;
- infection, even a simple cold: fever raises glucose considerably;
- physical or emotional stress, surgery, injury;
- corticosteroids, including a joint injection;
- insulin stored badly or out of date, or insufficient rotation of injection sites;
- less physical activity than usual;
- natural progression of the condition, which sometimes requires treatment to be adjusted.
In people without known diabetes
- undiagnosed diabetes or prediabetes;
- corticosteroids and some antipsychotics and diuretics;
- acute severe illness or infection;
- pancreatitis or pancreatic disease;
- Cushing's syndrome, acromegaly, hyperthyroidism;
- pregnancy — gestational diabetes.
What to do when glucose is high
- drink water: dehydration concentrates the glucose and makes everything worse;
- check whether you have missed a dose of medication;
- measure ketones if you have type 1 diabetes and glucose is above 14 mmol/L;
- move about a little, unless ketones are present: with positive ketones, exercise makes things worse;
- do not skip meals or try to compensate with prolonged fasting;
- do not adjust your insulin dose yourself unless you have an agreed plan with your doctor;
- if you are unwell, check glucose more often: during an infection you may need more medication, not less;
- write down the readings with the time, what you ate and what you did — that is what allows the pattern to be understood.
What to do over the medium term
- cut sugary drinks, fruit juice and refined flour;
- spread carbohydrate through the day and pair it with protein, fat and fibre;
- 150 minutes of activity a week plus two strength sessions: muscle is the largest consumer of glucose;
- lose 5–10% of body weight if you carry excess;
- sleep 7–9 hours: poor sleep raises glucose;
- stop smoking and moderate alcohol;
- review with your doctor any medicines that raise glucose;
- HbA1c checks every 3–6 months.
When to see a doctor
- a blood test has shown high glucose, even if you feel nothing;
- readings are persistently high despite treatment;
- the symptoms described above have appeared;
- you have an infection and your glucose has gone out of control;
- you have been prescribed corticosteroids and have diabetes or prediabetes;
- you are pregnant and high glucose has been found;
- you are alternating between very high and very low readings.
Common questions
Does one high reading mean I have diabetes? Not necessarily. It can be due to infection, stress or a medicine. The test needs repeating.
Can I lower it with diet alone? In prediabetes and early type 2 diabetes, often yes. In other cases medication is needed.
Does fruit raise blood sugar? Whole fruit does, moderately. Juice does so sharply.
Why is it high in the morning when I have not eaten? Because of the natural hormonal rhythm at dawn. This is common and is handled by adjusting treatment, not by skipping dinner.
Does stress raise glucose? Yes, directly, through cortisol and adrenaline.
Online consultation
In an online consultation the doctor interprets your readings and HbA1c, distinguishes a one-off elevation from diabetes, reviews medicines that may be raising your glucose, explains what to do during an illness, and sets up a monitoring plan.
This material is for information only and does not replace a medical consultation.
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Reviewed on Jul 2, 2026
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