Recognising Highs and Lows (Blood Glucose)

Intro

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.

Key Points

Low (hypo): usually <3.9 mmol/L (70 mg/dL). Treat immediately with fast carbs.
High (hyper): commonly >13.9 mmol/L (250 mg/dL). Check ketones if very high or if unwell.
CGM trend arrows matter as much as the number.
Repeat hypoglycaemia or persistent highs → review regimen with your diabetes team.

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

Take 15–20 g fast carbs (glucose tabs/gel, juice, regular soda).
Recheck in 15 minutes.
If still <3.9 mmol/L (70 mg/dL), repeat step 1.
If the next meal is >1 hour away, add a slow carb (toast/crackers).
If unconscious or can’t swallow: a trained person should give glucagon (nasal or injection) and call emergency services.

Common triggers

Too much insulin / 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 (seek urgent care)

What to do

If >13.9 mmol/L (250 mg/dL):
- Check ketones (blood or urine) if you’re on insulin or feel unwell.
- If ketones are present: follow sick-day rules (fluids, correction insulin per plan) and seek advice if not improving.
Take a correction dose as per your plan; recheck in 2–3 hours.
Hydrate (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 for rapid changes or when CGM readings don’t match how you feel.
Use trend arrows to act early (e.g., take carbs before a steep drop).
Log patterns: time of day, meals, exercise, alcohol, illness.

Prevention

Review basal/bolus ratios and timing with your team.
For exercise: plan carbs/insulin adjustments; beware of late-onset 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 any week.
Recurrent morning or overnight lows.
Persistent highs despite correction, or positive ketones that don’t settle.
Vomiting, abdominal pain, or breathing changes with high glucose.

FAQ

Do I always need to eat after correcting a low?
If the next meal is far away, add a small slow carb after you’re back above 3.9 mmol/L.

Can stress alone raise glucose?
Yes—stress hormones can push levels higher; adjust with guidance if it becomes a pattern.

Why do I wake up high after feeling low overnight?
Could be rebound after an untreated low or the dawn phenomenon—use overnight data to distinguish.