Low blood sugar (hypoglycaemia)
Treat first, recheck in 15 minutes, give a longer-acting carbohydrate, then find out why. A low caused by a sulfonylurea can last for a day or more.
At 4 a.m. a nurse calls: a 74-year-old man with type 2 diabetes is sweaty and confused. Sugar 42 mg/dL (2.3 mmol/L). He takes glibenclamide 10 mg twice daily and ate very little at dinner because of nausea. His creatinine is 2.1 mg/dL (186 µmol/L).
How do you treat him, and what happens next?
- Treat nowDo not wait for a lab glucose.
- Can he swallow safely?Yes: 15–20 g fast sugar by mouth. No: IV 10% dextrose, or glucagon IM if no IV access.
- Recheck in 10–15 minutesRepeat treatment if still below 70 mg/dL (3.9 mmol/L), up to 3 times.
- Once above 70 mg/dL, give a longer-acting carbohydrateBread, roti, biscuits, a meal, or milk.
- Sulfonylurea or kidney failure?Expect it to come back. 10% dextrose infusion and hourly sugar.
- Alcohol or malnourished?Thiamine with the glucose.
- Find the causeMissed meal, too much insulin, kidney failure, sepsis, alcohol, adrenal.
- Never stop basal insulin in type 1 diabetesReduce it if needed, but do not omit it.
- Drowsy, unconscious or fitting
- Lows that keep coming back, or caused by a sulfonylurea
- Not responding to treatment
- Unexplained low in someone not on diabetes medicines
- Prolonged sulfonylurea-induced hypoglycaemia
- Missed meals or nil by mouth with insulin running
- Sepsis
- Kidney or liver failure
- Alcohol
- Adrenal insufficiency
| Hypoglycaemia | Sugar below 70 mg/dL (3.9 mmol/L). Treat anything below 72 mg/dL (4 mmol/L) in a patient on insulin or a sulfonylurea |
| Can swallow | 15–20 g fast sugar: 150–200 mL juice, 4–5 glucose tablets, or 3–4 teaspoons of sugar in water |
| Cannot swallow | 10% dextrose 150–200 mL IV over 15 minutes |
| No IV access | Glucagon 1 mg IM |
| Sulfonylurea low | 10% dextrose infusion and hourly sugar for at least 24 hours |
Check every dose against a current drug reference and your hospital protocol.
On this page
Recognising it
- Sweating, shaking, fast heartbeat
- Hunger, anxiety, pale
- May be absent in long-standing diabetes or on beta-blockers
- Confusion, odd behaviour, slurred speech
- Weakness that can look like a stroke
- Drowsiness, fits, coma
Check the sugar in every confused, drowsy, fitting, aggressive or "stroke" patient. Low sugar is quick to find, quick to treat, and fatal if missed.
Treatment
- Sugar below 70 mg/dL (3.9 mmol/L)Confirm on a meter.
- Give 15–20 g fast sugarBy mouth if alert and can swallow. IV dextrose if not.
- Wait 10–15 minutes and recheckStill below 70: repeat, up to 3 times.
- Still low after 3 treatments, or worseningIV dextrose, senior review.
- Above 70 mg/dLGive a longer-acting carbohydrate: bread, roti, biscuits, milk, or the next meal.
- Look for the causeAnd adjust the insulin or tablets.
- Avoid 50% dextrose through small peripheral veins where 10% or 20% is available: it is very irritant and can damage tissue if it leaks. If 50% is the only option, use a large vein and flush well.
- Chocolate is not ideal: the fat slows sugar absorption.
Sulfonylurea lows
These tablets keep releasing insulin for many hours. A low that responds to treatment will often come back, especially in the elderly and with kidney failure. Glibenclamide (still widely used in Pakistan) is the most likely to cause long, severe lows.
- Admit.
- 10% dextrose infusion (often 50–100 mL/hour) after the initial treatment.
- Hourly sugar for at least 24 hours (longer with glibenclamide or kidney failure).
- Stop the sulfonylurea. Discuss a safer alternative with your senior.
- Persistent lows despite dextrose: senior advice (octreotide is sometimes used).
Finding the cause
- Too much insulin: dose error, wrong insulin, wrong time, injection given but meal missed.
- Missed or small meals: nil by mouth for a test, nausea, poor appetite, Ramadan fasting.
- Kidney failure: insulin and sulfonylureas last longer.
- Liver failure, sepsis, alcohol, adrenal insufficiency.
- More exercise than usual.
- No diabetes and no diabetes drugs? Senior review: take blood for insulin, C-peptide and sulfonylurea screen during the low, before treating if it can be done without delay.
Preventing the next one
- Review the insulin or tablets. Reduce doses in elderly patients, kidney failure and when eating less.
- Patients on insulin who are nil by mouth: follow your hospital's variable-rate insulin or basal-continue policy. Never stop basal insulin in type 1 diabetes: they will go into DKA.
- Teach the patient and family to recognise and treat lows, and always carry sugar.
- Ramadan: patients on insulin or sulfonylureas need a plan before fasting. Advise breaking the fast if sugar falls below 70 mg/dL (3.9 mmol/L).
- Driving: no driving until 45 minutes after treating a low.
Common mistakes
- Not checking the sugar in a confused or drowsy patient.
- Treating once and not rechecking.
- Sending a glibenclamide low home after one normal reading.
- Stopping all insulin in a type 1 diabetic who is not eating.
- Giving glucagon to a malnourished or alcoholic patient and expecting it to work.
- Forgetting the longer-acting carbohydrate after the sugar comes up.
Frequently asked questions
What is the treatment of hypoglycaemia?
If the patient can swallow, 15–20 g of fast-acting sugar by mouth, rechecked after 10–15 minutes. If not, 150–200 mL of 10% dextrose IV, or glucagon 1 mg IM if there is no IV access. Then a longer-acting carbohydrate.
What blood sugar level is hypoglycaemia?
Below 70 mg/dL (3.9 mmol/L). Below 54 mg/dL (3.0 mmol/L) is clinically significant hypoglycaemia.
Why are sulfonylurea lows dangerous?
They can last for many hours or days and recur after initial treatment, especially with glibenclamide, in the elderly and in kidney failure.
What is the immediate treatment for hypoglycemia?
15–20 g of fast-acting sugar by mouth if the patient can swallow, or 150–200 mL of 10% dextrose IV if not, rechecking after 10–15 minutes and then giving a longer-acting carbohydrate.
Test yourself
Exam-style questions on this guide, from our two question banks. Choose an answer to see why each option is right or wrong.
1. A drowsy patient who cannot swallow has a glucose of 2.7 mmol/L (48 mg/dL). An IV cannula is in place. What should be given?
Answer: 10% dextrose 150–200 mL IV over 15 minutes. In hypoglycaemia with impaired consciousness, give IV 10% dextrose, recheck after 10–15 minutes and repeat if still low.
- 50% dextrose 100 mL as first choice: 10% is safer for veins.
- Wait for the lab glucose: Treat now.
- Oral glucose gel: Unsafe if drowsy.
- Insulin: Wrong direction.
2. A patient on glibenclamide had hypoglycaemia, now corrected to 6.2 mmol/L (112 mg/dL). What is the best plan?
Answer: Admit for dextrose and monitoring. Sulfonylurea hypoglycaemia can recur for 24–72 hours. Admit, monitor and stop the drug.
- Discharge with advice: Sulfonylureas cause prolonged hypoglycaemia.
- Increase the glibenclamide: Wrong.
- Recheck once at 4 hours: Not enough.
- Give glucagon and discharge: Can worsen with sulfonylureas.
3. A patient with type 1 diabetes is nil by mouth for surgery tomorrow. What should be done with his insulin?
Answer: Continue basal insulin. People with type 1 diabetes need basal insulin even when fasting.
- Give insulin only if glucose is above 20: Basal insulin is always needed.
- Stop all insulin: Risks DKA.
- Switch to oral metformin: Not for type 1.
- Double the basal insulin: Hypoglycaemia risk.
4. A man with type 2 diabetes on gliclazide is found drowsy and sweaty with capillary glucose 2.2 mmol/L. He cannot swallow safely. What is given?
Answer: IV 10% dextrose. Severe hypoglycaemia: if unable to swallow, give IV glucose (e.g. 150–200 mL of 10% dextrose over 15 min) or IM glucagon 1 mg (less effective in sulfonylurea overdose, alcohol and liver disease). Conscious patients: 15–20 g fast-acting carbohydrate, recheck in 15 min, then a long-acting carbohydrate. Sulfonylurea-induced hypoglycaemia can recur for 24–72 h — admit and monitor; octreotide for refractory cases.
- Oral glucose gel: Oral gel is unsafe if he cannot swallow.
- Variable insulin infusion: Insulin worsens hypoglycaemia.
- IV hydrocortisone: Hydrocortisone does not correct hypoglycaemia.
5. A woman with new diabetes, weight loss and a recent DVT has an erythematous, migratory, blistering rash with crusting around the groin and perioral area. What is the likely tumour?
Answer: Glucagonoma. Glucagonoma: alpha-cell pancreatic neuroendocrine tumour — necrolytic migratory erythema (characteristic; intertriginous and perioral, waxing and waning), diabetes/glucose intolerance, weight loss, glossitis/angular stomatitis, anaemia, venous thrombosis, depression; very high glucagon levels. Treatment: surgery, somatostatin analogues (rash improves), amino acid/zinc supplementation, anticoagulation.
- Insulinoma: Insulinoma causes hypoglycaemia, not diabetes.
- Carcinoid tumour: Carcinoid causes flushing, wheeze and diarrhoea.
- Phaeochromocytoma: Phaeochromocytoma causes paroxysmal hypertension.
6. Which hormone is released from the atria in response to stretch and promotes sodium excretion?
Answer: Atrial natriuretic peptide. ANP (atria) and BNP (ventricles) are released with stretch (volume overload, heart failure). They increase GFR (afferent dilatation, efferent constriction), inhibit sodium reabsorption in the collecting duct, inhibit renin and aldosterone, and cause vasodilatation. BNP/NT-proBNP is used to diagnose heart failure.
- Aldosterone: Retains sodium.
- Antidiuretic hormone: Retains water.
- Renin from the kidney: Starts the RAAS.
- Angiotensin II: Retains sodium, vasoconstricts.
7. A non-diabetic nurse has recurrent hypoglycaemia with high insulin and low C-peptide levels. What is the most likely cause?
Answer: Injected insulin. Proinsulin is cleaved into insulin and C-peptide in equal amounts, so endogenous insulin secretion raises both. Injected insulin contains no C-peptide and suppresses endogenous release: high insulin, low C-peptide. Insulinoma and sulfonylureas raise both (screen urine/blood for sulfonylureas to separate them).
- Insulinoma: High insulin and high C-peptide.
- Sulfonylurea overdose: High insulin and high C-peptide; drug screen positive.
- Addison's disease: Low insulin.
- Liver failure: Low insulin.
References and dose sources
- JBDS: The hospital management of hypoglycaemia in adults with diabetes
- ADA Standards of Care in Diabetes (2025)
- Dextrose (glucose) dosing: Drugs.com: Dextrose dosage (see also our dextrose (glucose) dose page)
- Glucagon dosing: Drugs.com: Glucagon dosage (see also our glucagon dose page)
- Thiamine (vitamin B1) dosing: Drugs.com: Thiamine dosage (see also our thiamine (vitamin b1) dose page)
International guidance is linked where it reflects good practice. Where your hospital’s protocol differs, follow your hospital.