Low blood glucose

Also known as hypoglycaemia

Low blood glucose or hypoglycaemia occurs when the blood glucose level is less than 4 mmol/l, or where symptoms of hypoglycaemia are experienced at a level close to this. Hypoglycaemia can be classified as mild, moderate or severe and needs to be reversed right away to prevent impact on the brain and risk of unconsciousness.

Key points

  1. In type 1 diabetes, a low blood glucose can occur due to the use of insulin. People with type 1 diabetes should always carry glucose or some form of sugar to take immediately if their blood glucose level goes low, which for most people is below 4mmol/L. It is recommended to wear a medical alert bracelet or carry identification that lists your normal insulin use. If hypos occur often, talk to your diabetes specialist.
  2. People with type 2 diabetes should only be at risk of a hypo if taking insulin or sulphonylurea tablets for their diabetes. If taking these medications you should always carry glucose or some form of sugar to have immediately if a hypo occurs. If you are getting hypos often, talk to your diabetes specialist.

What is hypoglycaemia?

Hypoglycaemia, or low blood glucose occurs when the blood glucose level is less than 4 mmol/l, or where symptoms of hypoglycaemia are experienced at a level close to this. The following video from Diabetes UK helps explain the common symptoms, causes and treatment. 


The usual causes of low blood glucose level are:

  • not eating enough carbohydrate with your meal (eg. steak and salad with no bread or potato)
  • missing or delaying a meal
  • missing snacks
  • doing physical activity without either adjusting your insulin (downwards) or taking more carbohydrate before, during or after physical activity
  • taking too much insulin
  • drinking alcohol in excess or without taking carbohydrate food and/or adjusting your insulin downwards.

If your blood glucose is low and your insulin can't be switched off, what happens?

The insulin continues to move the glucose into the body's cells. The liver doesn't start releasing stored glucose (remember, it only does this when it senses your insulin levels are low). So, your blood glucose level keeps going down and can soon be dangerously low. The liver does not correct your low glucose.


Symptoms of mild to moderate hypoglycaemia may include one or more of the following:

  • looking pale
  • feeling shaky, sweaty or suddenly unwell
  • suddenly feeling very hungry
  • a 'racing' heart
  • tingling around your mouth and tongue
  • headache
  • suddenly a little 'strange' as if you are unable to concentrate 
  • feeling dizzy
  • rapid change in behaviour or irritability
  • babies or children may start crying 
  • confusion
  • blurred vision.

Babies and young children may show few signs of low blood sugar, so be on the alert if they have diabetes. 

Over time you will come to recognise the feelings you get when your blood glucose goes low.

Severe hypoglycaemia
The symptoms of severe hypoglycaemia are a blood glucose level less than 4 mmol/l and:

  • extreme drowsiness or disorientation
  • being unconscious, or
  • having a convulsion.

Severe hypoglycaemia is a medical emergency and you should call 111 or emergency services straight away. 


If you feel you have time, check your blood glucose on the meter your doctor will have given you. Sometimes it may be something else that has made you feel unwell. But if in doubt, or if you are feeling very unwell, go ahead and treat your low blood glucose anyway.

Always remember 'if in doubt, treat'.

Eat or drink one serving of a quick-acting carbohydrate. Each of these represents one serving, eg, 6 jelly beans = one serving:
  • 3 teaspoons of glucose powder in water, or
  • 3 Dextro Energy tablets, or
  • 3 Vita Glucose tablets (available from pharmacies), or
  • 3 teaspoons of honey or jam or sugar, or
  • a small glass (150ml) of sugar-sweetened lemonade [not diet] or cordial, or
  • 6 large jelly beans.

2. After 10 minutes test your blood glucose again. If it is still less than 4mmol/L, eat another serving of quick-acting carbohydrate (see list above).

3. Once your blood glucose is above 4mmol/L - if it is your mealtime, eat your meal.

4. Otherwise eat or drink a snack such as a slice of bread or pottle of yoghurt. 

Treatment for serious hypoglycaemia 

A serious low blood glucose level is classified as one you need the help of another person to correct. 

If the person is conscious and able to eat or drink, treatment is the same as above. Sometimes it can be easier to suck on a teaspoon of honey rather than suck glucose tablets. If a person has any difficulty swallowing, stop. 

Call an ambulance if you find the person unconscious.

If a person is unconscious from a hypoglycaemia episode, place the person in the recovery position (lying on their left side with right leg hooked over the top of the left leg so they are leaning over, chin extended). Do not give them anything by mouth as the risk of choking is high. an unconscious person can choke if you put something in their mouth). If glucagon is available and you know how to give it, then give right away. If not, call an ambulance.

After any serious hypo, write down any possible triggers, what happened and visit your diabetes specialist team to discuss what changes are needed to prevent further episodes. 

Glucagon injections

Glucagon is a naturally occurring hormone (also produced by the pancreas) that works in the opposite way to insulin. When blood glucose levels go too low, glucagon is released and this stimulates several processes to release glucose from the liver and fat stores into the bloodstream.

Glucagon can be used as a treatment for serious hypoglycaemia. It comes as an auto-injector and can be given to someone with diabetes who is unconscious with a low blood glucose level.

Talk with your diabetes specialist team about whether a glucagon injection would be right for you. It can be a valuable addition to your emergency snack pack, especially if you do extreme sports, have little warning of hypos or are a parent of a child with type 1 diabetes who's eating and activity levels are harder to plan. If given, make sure your family or friends receive the training needed to know how and when to use. 

Self care

Wear identification

If you have type one diabetes or are on medications that raise the risk of hypoglycaemia, be wise and wear a Medic Alert bracelet or necklace. Even with the best of care and planning, unexpected events can happen to trigger a serious hypoglycaemic episode. If this happens, an alert bracelet helps anyone assisting you to know what to do or to alert emergency services that you have diabetes. Without identification, there can be increased delays in receiving the right treatment as people try to work out what is wrong.  

Manage low blood glucose early

Learn to recognise your early warning signs of having a hypo. Be alert to what these are and test your blood glucose levels if any of these symptoms develop. Also make sure to always carry your emergency treatment snack with you. Keep in your bag, at work and home so you can treat low blood glucose early before it becomes more serious.  

Learn more

Hypoglycaemia in children Kids Health NZ
Hypoglycaemia Diabetes Info NZ
Diabetes section Ministry of Health 
Diabetes NZ

Credits: Editorial team. Last reviewed: 18 Dec 2015