Diabetes

Recognising Highs and Lows (Blood Glucose)

2025-08-30 • Updated 2025-09-14

Recognising Highs and Lows (Blood Glucose)

Knowing the early signs of low (hypoglycaemia) and high (hyperglycaemia) blood glucose helps you treat quickly and avoid complications. This guide gives clear symptoms, numbers, and step-by-step actions.

🚑 Bottom Line

• Low = <3.9 mmol/L (70 mg/dL) → treat immediately with 15 g fast carbs.
• High = >13.9 mmol/L (250 mg/dL) → check ketones, give correction insulin, hydrate.
• If severe symptoms, vomiting, or ketones ≥3.0 mmol/L → call emergency services.

Hypoglycaemia (Low)

Typical symptoms

• Shaky, sweaty, hungry, tingling lips, palpitations
• Headache, blurred vision, difficulty concentrating, irritability
• Severe: confusion, drowsiness, seizures, unconsciousness

Immediate treatment — Rule of 15

1. Take 15–20 g fast-acting carbs (glucose tabs/gel, juice, regular soda).
2. Recheck in 15 minutes.
3. If still <3.9 mmol/L (70 mg/dL), repeat step 1.
4. If the next meal is >1 hour away, add a slow carb (toast, crackers).
5. ⚠️ If unconscious or unable to swallow: a trained person should give glucagon (nasal or injection) and call emergency services.

Common triggers

• Too much insulin or delayed meals
• Exercise (during or up to 24h after)
• Alcohol (especially without food)

Hyperglycaemia (High)

Typical symptoms

• Thirst, frequent urination, tiredness
• Blurred vision, headache
• If very high: abdominal pain, nausea/vomiting, deep/fast breathing → urgent care

What to do

• If >13.9 mmol/L (250 mg/dL):
  • Check ketones (blood or urine) if on insulin or unwell.
  • If ketones are present: follow Diabetes Emergency Actions.
• Take a correction dose as per your plan; recheck in 2–3 hours.
• Hydrate with water; avoid sugary drinks until back in range.

Common triggers

• Illness/infection, stress hormones
• Missed insulin doses or pump/infusion set issues
• Carb counting errors

Monitoring & Trends

• Finger-stick remains the reference when CGM readings don’t match symptoms.
• Use trend arrows to act early (e.g., carbs before a steep drop).
• Log patterns: time of day, meals, exercise, alcohol, illness.

Prevention

• Review basal/bolus ratios and timing with your team.
• Plan carbs/insulin adjustments around exercise; beware of delayed lows.
• Rotate infusion/sensor sites; check for leaks or dislodgement.
• Set sensible CGM alerts (overnight slightly higher for safety).

When to Seek Medical Advice

• Two or more severe hypos (needing help) in a week.
• Recurrent morning or overnight lows.
• Persistent highs despite corrections, or positive ketones not settling.
• Vomiting, abdominal pain, or breathing changes with high glucose.

FAQ

Do I always need to eat after correcting a low?
If your next meal is far away, yes—add a slow carb after recovering above 3.9 mmol/L.

Can stress raise glucose?
Yes. Stress hormones often push levels higher. Adjust with team guidance if it’s a pattern.

Why do I wake up high after a low?
Could be a rebound after an untreated low or the dawn phenomenon. Overnight CGM or a 3 a.m. finger-stick helps tell the difference.

Further Reading

• NHS — Hypoglycaemia
• ADA — Hyperglycemia
• ISPAD Guidelines — Hypoglycaemia and Hyperglycaemia (2022)

Related Guides

• Type 1 Diabetes — Managing Hypoglycaemia
• Night-time Hypoglycaemia
• Diabetes Emergency Actions — Hypos, Highs, and Ketones
• Type 1 Diabetes — Sick-Day Management
• Managing Type 1 Diabetes During Exercise
• Insulin Types Explained

Educational only; not a substitute for professional medical advice.

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• #hyperglycaemia
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• #patientguide