Overview
Hypoglycaemia in Adults
Clinical Overview
Summary
Hypoglycaemia is defined as blood glucose below 4.0 mmol/L. In diabetic patients, it is most commonly caused by insulin or sulphonylureas with inadequate carbohydrate intake. Severe hypoglycaemia can cause seizures, coma, and brain damage. Treatment depends on consciousness: oral glucose if conscious, IV dextrose or IM glucagon if unconscious.
Key Facts
- Definition: Blood glucose below 4.0 mmol/L ("4 is the floor")
- Severe hypoglycaemia: Requiring third-party assistance
- Neuroglycopenic symptoms: Appear at glucose below 3.0 mmol/L
- Brain damage threshold: Prolonged glucose below 2.0 mmol/L
- Sulphonylurea hypoglycaemia: Can recur — observe for 24-48 hours
Clinical Pearls
"4 is the floor" — treat any glucose below 4.0 mmol/L even if asymptomatic
Sulphonylurea-induced hypoglycaemia can last 24-72 hours — ADMIT
Rebound hyperglycaemia after treatment is common — avoid overtreating
Why This Matters Clinically
Hypoglycaemia is the major limiting factor to achieving good glycaemic control in diabetes. Repeated episodes cause impaired awareness, creating a dangerous cycle. Recognition and appropriate treatment prevents serious neurological sequelae.
Epidemiology
Incidence
- Type 1 diabetes: 1-2 severe episodes per patient per year
- Type 2 diabetes on insulin: 0.3-0.5 episodes per patient per year
- Type 2 diabetes on sulphonylureas: 0.2-0.4 episodes per patient per year
Risk Factors
| Factor | Mechanism |
|---|---|
| Insulin/sulphonylurea use | Excess insulin effect |
| Missed meals | Inadequate glucose intake |
| Exercise | Increased glucose utilisation |
| Alcohol | Impaired gluconeogenesis |
| Renal impairment | Reduced drug clearance |
| Long diabetes duration | Hypoglycaemia unawareness |
| Previous severe hypoglycaemia | Predictive of future events |
Pathophysiology
Normal Counter-Regulatory Response
- Falling glucose: Insulin secretion stops
- Glucose ~3.6 mmol/L: Glucagon release
- Glucose ~3.2 mmol/L: Adrenaline release
- Lower levels: Cortisol, GH release
Failure in Diabetes
- Exogenous insulin cannot be "switched off"
- Type 1: Glucagon response lost within 5 years
- Repeated hypos: Impaired adrenaline response → unawareness
Symptoms by Mechanism
| Autonomic (Adrenergic) | Neuroglycopenic |
|---|---|
| Sweating | Confusion |
| Tremor | Drowsiness |
| Palpitations | Difficulty speaking |
| Hunger | Incoordination |
| Anxiety | Seizures |
Classification
By Severity (International Hypoglycaemia Study Group)
| Level | Glucose | Clinical |
|---|---|---|
| Level 1 (Alert) | Below 4.0 mmol/L | Symptomatic, self-treatable |
| Level 2 (Serious) | Below 3.0 mmol/L | Neuroglycopenic symptoms |
| Level 3 (Severe) | Any | Requires third-party assistance |
By Cause
- Fasting hypoglycaemia: Insulinoma, adrenal insufficiency, liver failure
- Reactive hypoglycaemia: Post-prandial, dumping syndrome
- Drug-induced: Insulin, sulphonylureas, alcohol
Investigations
Immediate
- Capillary blood glucose: Confirm hypoglycaemia
- Venous glucose: If CBG uncertain
- Lab glucose during episode: Gold standard (Whipple's triad)
If Cause Unclear (Non-Diabetic)
- C-peptide + insulin: During hypoglycaemic episode
- Beta-hydroxybutyrate: Suppressed in insulinoma
- Sulphonylurea screen: Rule out factitious/accidental
- Cortisol: Adrenal insufficiency
- IGF-1, IGF-2: Non-islet cell tumours
- Liver and renal function: Impaired metabolism
Whipple's Triad (Diagnostic)
- Symptoms of hypoglycaemia
- Documented low blood glucose
- Symptom resolution with glucose administration
Management
Conscious Patient (Self-Treating)
Oral fast-acting glucose:
- 15-20g fast-acting carbohydrate
- Examples: Lucozade 100ml, glucose tablets ×4, orange juice 200ml
- Recheck glucose after 15 minutes
- Repeat if still below 4.0 mmol/L
- Follow with long-acting carbohydrate (biscuits, bread)
Unconscious/Unable to Swallow
IM Glucagon:
- Dose: 1mg IM (or SC)
- Onset: 10-15 minutes
- Less effective if: Alcohol, liver disease, prolonged fast
IV Dextrose:
- 10% glucose: 150-200ml over 15 minutes (preferred)
- 20% glucose: 75-100ml via large vein
- 50% glucose: Avoid if possible (vesicant, phlebitis)
Special Situations
Sulphonylurea-Induced:
- Admit for 24-48 hours observation
- IV dextrose infusion may be needed
- Consider octreotide 50mcg SC if recurrent
Post-Gastric Surgery:
- Dumping syndrome
- Small frequent meals, low GI carbohydrates
Prevention
- Structured education (DAFNE for Type 1)
- CGM with alarms if hypoglycaemia unawareness
- Review insulin/sulphonylurea doses
- Glucagon kit prescription
Complications
Acute
- Seizures
- Aspiration
- Cardiac arrhythmias (QT prolongation)
- Injuries from falls
- Road traffic accidents
Long-term
| Complication | Impact |
|---|---|
| Hypoglycaemia unawareness | 6× risk of severe hypoglycaemia |
| Cognitive impairment | Risk with recurrent severe episodes |
| Cardiovascular events | Arrhythmias, ischaemia during hypos |
| Quality of life | Fear of hypoglycaemia affects control |
Prognosis
Outcomes
- Most episodes: Resolve without sequelae
- Severe prolonged hypoglycaemia: Can cause permanent brain damage
- Dead-in-bed syndrome: Rare, young Type 1 patients
Risk of Recurrence
- Previous severe hypo: Strongest predictor
- Impaired awareness: 6× increased risk
- Long duration of diabetes: Progressive risk
Key Evidence
Key Studies
DCCT/EDIC PMID: 8366922
- Intensive insulin therapy reduced microvascular complications
- Increased hypoglycaemia (62 vs 19 per 100 patient-years)
ACCORD PMID: 18539917
- Intensive control in Type 2 increased mortality
- Hypoglycaemia implicated as possible mechanism
Guidelines
- JBDS Hypoglycaemia Guidelines (2022)
- ADA Standards of Care 2024
- NICE NG28 Type 2 Diabetes
Patient & Family Information
What is Hypoglycaemia?
Hypoglycaemia (a "hypo") happens when your blood sugar drops too low. It can make you feel shaky, sweaty, and confused. If not treated quickly, it can cause you to pass out.
Warning Signs
- Feeling shaky or trembling
- Sweating
- Feeling hungry
- Confusion or difficulty concentrating
- Feeling anxious or irritable
What to Do
If you can swallow:
- Take 15-20g of fast-acting sugar (juice, glucose tablets, sweets)
- Wait 15 minutes
- Recheck and repeat if still feeling unwell
- Eat something substantial afterwards
If someone is unconscious:
- Put them in the recovery position
- Give glucagon injection if trained
- Call 999
Prevention Tips
- Regular meal times
- Always carry fast-acting glucose
- Check blood sugar before driving
- Tell people around you about hypos