Low Blood Sugar (Hypoglycaemia): Symptoms, Causes, First Aid and Prevention

Hypoglycaemia, or low blood sugar, happens when glucose falls too far to supply the brain and body with energy. It is the most common acute complication of diabetes treated with insulin or certain tablets, and it can come on in minutes. Most episodes are mild and easily treated, but severe ones can cause fits, loss of consciousness, accidents and rarely death. Knowing how to recognise and treat it is vital for everyone with diabetes and their families.

Definition and levels

• Level 1 (alert): below 70 mg/dL (3.9 mmol/L), time to treat
• Level 2 (serious): below 54 mg/dL (3.0 mmol/L)
• Level 3 (severe): any low level with confusion or unconsciousness needing help from another person

Compare these with normal blood sugar levels.

Symptoms

Early warning signs come from adrenaline:

• Shaking or trembling, sweating, pale skin
• Fast heartbeat, anxiety
• Hunger, nausea
• Tingling lips

As sugar falls further, brain symptoms follow:

• Headache, blurred vision
• Difficulty concentrating, confusion, slurred speech
• Irritability, strange behaviour (sometimes mistaken for intoxication)
• Weakness, drowsiness
• Fits, loss of consciousness

At night, signs include night sweats, nightmares, restless sleep, and waking with a headache or feeling unrested.

Causes in people with diabetes

• Too much insulin or the wrong dose or type
• Tablets that stimulate insulin release: sulfonylureas such as gliclazide, glibenclamide and glimepiride
• Missed or delayed meals, or less carbohydrate than planned
• Unplanned or intense exercise, which can lower sugar for many hours afterwards
• Alcohol, especially on an empty stomach
• Kidney or liver disease, which slows medicine clearance
• Weight loss or improved control without adjusting medicines
• Vomiting or diarrhoea
• Fasting periods, such as religious fasting, without a medical plan

Metformin, SGLT2 inhibitors, DPP-4 inhibitors and GLP-1 medicines rarely cause low sugar on their own, but they can when combined with insulin or sulfonylureas.

What to do: the 15-15 rule

If the person is awake and able to swallow:

1. Check blood sugar if possible. If you cannot test but have symptoms, treat anyway.
2. Take 15 g of fast carbohydrate: 3-4 glucose tablets, half a cup (about 120 mL) of fruit juice or regular soft drink, or one tablespoon of sugar or honey in water.
3. Wait 15 minutes and recheck.
4. Repeat if sugar is still below 70 mg/dL.
5. Follow with a snack or meal containing starch and protein, such as bread, biscuits or a banana, if the next meal is more than an hour away.

Do not use chocolate or high-fat foods for the first treatment because they raise sugar more slowly. Avoid overtreating, which causes a rebound high.

If the person is unconscious, fitting or cannot swallow

• Do not put food or drink in the mouth, because of choking.
• Lay them on their side in the recovery position.
• Call an ambulance (1990 in Sri Lanka) or take them to the nearest hospital.
• Give glucagon by injection or nasal spray if it is available and you are trained. People on insulin, especially those with previous severe lows, should discuss getting a glucagon kit.
• In hospital, glucose is given by drip.

After any severe episode, tell your doctor, because treatment usually needs adjusting.

Hypoglycaemia unawareness

After repeated lows, the body's warning symptoms can fade, so the first sign may be confusion. This is dangerous. Strict avoidance of lows for several weeks often restores warning signs. Continuous glucose monitors with alarms are especially helpful. Discuss new targets, medicines and monitoring with your doctor.

Preventing low blood sugar

• Take medicines exactly as prescribed, and do not take extra doses.
• Eat regular meals, and do not skip meals after taking insulin or sulfonylureas.
• Check your sugar more often when you change doses, exercise, are ill or travelling.
• Carry fast sugar everywhere, and keep it by the bed and in your bag and vehicle.
• Adjust food or insulin around exercise as advised, and snack beforehand if sugar is low.
• If you drink alcohol, have food, drink in moderation, and check sugar before bed.
• Talk to your doctor before fasting.
• Wear a medical ID or carry a card stating you have diabetes and what you take.
• Make sure family, friends, teachers or co-workers know the signs and what to do.
• Review your HbA1c target if you have frequent lows. Older adults and people with kidney disease may need a less strict target (see HbA1c explained).

Driving and work

Check your sugar before driving, and do not drive if it is below about 90 mg/dL (5.0 mmol/L), until you have had a snack and recovered. If you feel a low coming while driving, pull over safely, remove the keys, treat it, and wait at least 30-45 minutes after recovery before driving again. Check local licensing rules and your insurer's requirements.

Low blood sugar without diabetes

Occasionally, people without diabetes develop low sugar after prolonged fasting, heavy drinking, severe illness, medicines such as some antimalarials and beta-blockers, adrenal or pituitary problems, bowel surgery, or very rarely an insulin-producing tumour. If you have repeated episodes of confusion, sweating or fainting relieved by eating, see a doctor for testing during a symptom episode.

When to see a doctor

See a doctor if you have more than one or two lows a week, any severe low, night-time lows, or lows without warning. Medicines often need to be changed. Also see the guide on diabetic foot care and diabetes and kidney disease for other important checks.

References

• American Diabetes Association: Standards of Care in Diabetes, glycaemic goals and hypoglycaemia
• International Hypoglycaemia Study Group: glucose concentrations of less than 3.0 mmol/L as a threshold for clinically important hypoglycaemia
• Joint British Diabetes Societies: management of hypoglycaemia in adults
• World Health Organization: diabetes fact sheet