Low blood glucose

Also known as hypoglycaemia or a 'hypo'

Low blood glucose or hypoglycaemia occurs when your blood glucose level goes low, which for most people is below 4mmol/L. You need to take glucose or some form of sugar immediately and follow this with some food.

On this page, you can find the following information:

Key points about hypoglycaemia (low blood glucose)

  1. Hypoglycaemia needs to be treated right away to prevent the risk of unconsciousness.
  2. Treatment is to have 10 to 15g of a quick-acting carbohydrate (glucose tablets/sugar/juice/jelly beans) immediately, then retest your glucose level in 10 minutes. If it is above 4 mmol/L, have a carbohydrate snack (sandwich/crackers). If it is still below 4 mmol/L, repeat the glucose and retest in 10 minutes.
  3. If you have type 1 diabetes, low blood glucose can occur due to having too much insulin or not enough food.
  4. If you have type 2 diabetes, you should only be at risk of hypoglycaemia if you are taking insulin or sulphonylurea tablets for your diabetes and miss or delay your meal.
  5. With both type 1 or type 2 diabetes, if you are getting hypos often talk to your GP, nurse or diabetes specialist.
  6. It is recommended that people with diabetes wear a medical alert bracelet – this can alert people you may have hypoglycaemia if you are unable to ask for help.
Severe hypoglycaemia is a medical emergency. Call 111 and ask for an ambulance if someone has a blood glucose level less than 4 mmol/l and any one of the following:
  • is extremely drowsy or disorientated
  • is unconscious
  • is having a convulsion (fit).

What is hypoglycaemia?

Hypoglycaemia (a hypo) or low blood glucose occurs when your blood glucose level is less than 4 mmol/L, or where symptoms of hypoglycaemia are experienced at a level close to this.

Normally, when blood glucose lowers, your body lowers the amount of insulin it is putting out. This stabilises blood glucose by stopping glucose moving into your body’s cells and releasing stored glucose from your liver. This may not happen if you have diabetes.

When you have diabetes and are taking insulin (and some diabetes medicines), you can still get the same low blood glucose level if you run out of glucose coming in from your food. But when your body senses that your blood glucose is becoming lower and it tries to switch off its insulin, it can’t. This is because you have injected your insulin (and you can’t switch this off). 

This means the insulin continues to move glucose into your body’s cells and your liver doesn’t start releasing stored glucose. So, your blood glucose level keeps going down and can soon be dangerously low. 

Because your brain needs glucose all the time to function, if you cut off the supply of glucose and do not take action, you will eventually become unconscious.

The following video from Diabetes UK helps explain the common symptoms, causes and treatment. 

(Diabetes.co.uk, 2012)

What are the symptoms of hypoglycaemia?

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
  • confusion
  • blurred vision.

Over time you come to recognise the feelings you get when your blood glucose goes low. However, if you have had diabetes for a long time, you may not get any symptoms when your blood glucose goes low.

What are the causes of hypoglycaemia?

The usual causes of low blood glucose level are:

  • not eating enough carbohydrate with your meal, eg, steak and salad with no carbohydrate such as bread/potato/kumara/rice/pasta
  • missing or delaying a meal
  • missing snacks (if you need them)
  • doing physical activity without either reducing your insulin 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 reducing your insulin.

How is hypoglycaemia treated?

If you feel you have time, check your blood glucose on your meter. It may be something else that has made you feel unwell. But if in doubt, or if you are feeling very unwell, treat your low blood glucose anyway.

Always remember 'if in doubt, treat'.

1. Eat or drink 1 serving (10 to 15g) of a quick-acting carbohydrate. Each of the following is 1 serving:

  • 3 teaspoons of glucose powder in water
  • (10–15g) of glucose tablets (available from pharmacies)
  • 3 teaspoons of jam or sugar
  • a small glass (150ml) of sugar-sweetened lemonade (not diet) or cordial
  • 6 large jelly beans/5 Mentos.

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

3. Once your blood glucose is above 4mmol/L, eat some carbohydrate food (sandwich/crackers) or if it's your mealtime, eat your meal.

What is the treatment for serious hypoglycaemia?

A serious low blood glucose level is classified as one you need the help of another person to treat. 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 jam than chew glucose tablets. If a person has any difficulty swallowing, do not put any food in their mouth. 

Call an ambulance if you find the person unconscious.

If a person is unconscious from a hypoglycaemia episode, place them 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). If Glucagon is available and you know how to give it, then give right away. (Note that Glucagon takes 10 minutes to work.) If not, call an ambulance. Do not give them anything by mouth as an unconscious person can choke if you put something in their mouth.

Glucagon injections

Glucagon is a naturally occurring hormone (also produced by your 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 your liver and fat stores into your bloodstream. However, 
injected Glucagon may need to be used as a treatment for serious hypoglycaemia. It comes as in a kit and can be given to someone with diabetes who is unconscious with a low blood glucose level.

Ask your diabetes specialist team whether a Glucagon injection is right for you. It can be a valuable addition to your emergency pack, especially if you do extreme sports or have little warning of hypos. It is also useful if you are a parent of a child with type 1 diabetes, whose eating and activity levels are harder to plan.

If you are given a Glucagon kit, make sure your family or friends receive the training needed to know how and when to use it. 

How can I care for myself with hypoglycaemia?

Wear identification

If you have type 1 diabetes or are on medicines 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 helping you 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 (glucose/food) with you. Keep it in your bag, at work and at home so you can treat low blood glucose early before it becomes more serious.  


If you have mild hypoglycaemia, the law states that you must not drive for 1 hour after that. If you have severe hypoglycaemia (when you need someone else's help to deal with it), you must not drive for 24 hours.

People who experience severe hypoglycaemia while driving should not drive for at least a month, whether you're involved in a crash or not. It’s likely you’ll need to see a specialist before you can safely return to driving, and you’ll need to talk to your doctor. 

Read more about diabetes and driving

Learn from a hypo

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

Learn more

Hypoglycaemia in children KidsHealth, NZ
Hypoglycaemia Diabetes Info NZ
Diabetes section Ministry of Health, NZ
Diabetes NZ 

Reviewed by

Terrie Spedding is a diabetes clinical nurse specialist working for Health Hawke’s Bay PHO. She has with 30+ years’ experience in all aspects of the care, management and support of people with diabetes, presently working in the primary care sector. She also has an interest in diabetes research. 
Credits: Health Navigator Editorial Team. Reviewed By: Terrie Spedding, Diabetes Clinical Nurse Specialist, Health Hawke’s Bay PHO Last reviewed: 23 Mar 2021