Cystic fibrosis (CF) can cause a build-up of sticky mucus and inflammation in the pancreas. This can prevent the pancreas from producing insulin properly. Insulin controls the amount of sugar in our blood. When the pancreas can’t produce enough insulin, blood sugar levels can rise and this can lead to CF diabetes (CFD).
What is cystic fibrosis diabetes (CFD)?
Cystic fibrosis diabetes (CFD) is a common complication of cystic fibrosis (CF). CFD is a condition linked to a small organ called the pancreas. Most people with CF are pancreatic insufficient, which means the pancreas doesn’t work properly. The pancreas is an organ which has two important functions:
- making enzymes to help digest your food
- making a hormone called insulin, which is important for keeping your blood glucose levels under control.
Your body converts the food you eat into energy. You need this energy for exercise, everyday activities, and thinking. Most of this energy comes from carbohydrates, which are broken down into glucose. Insulin has the job of moving this glucose from your blood stream into your cells where it can be used for energy. In CFD, the pancreas makes some insulin, but not enough. This can lead to high blood glucose levels.
How common is CFD?
Cystic fibrosis diabetes is common in adults and young people with CF. Data from the UK CF Registry 2022 indicates that almost a third of people with CF over the age of 10 will develop CFD. The chance of developing CFD increases with age.
How is CFD different to other types of diabetes?
There are several different types of diabetes, but the most common types in people who don’t have CF are type 1 and type 2. Although people with CF can develop these types of diabetes, CFD is a different condition to both. Type 1 diabetes occurs when the body does not produce any insulin. Type 2 diabetes occurs when the body is not using insulin in the right way, known as ‘insulin resistance’. CFD can have features of both type 1 and type 2 diabetes. In CFD, the pancreas makes some insulin, but not enough.
Other aspects of CF can make people less able to respond to insulin, such as when nutrition is poor or when chest infection leads to inflammation. Drugs such as steroids, which some people with CF need, can also reduce the body’s sensitivity to insulin.
What are the symptoms of CFD?
Many people don’t have any signs or symptoms of CFD. This is why yearly screening for CFD is important, which usually starts from the age of 10 years. In others, the first sign of CFD may be a decline in weight and lung function.
How is CFD diagnosed?
There are different ways to screen for CFD, such as:
- serial blood glucose monitoring or continuous glucose monitoring (CGM)
- oral glucose tolerance test (OGTT)
Your CF centre will let you know which test they use. The different types of screening tests are described in our Management of Cystic Fibrosis Diabetes guideline.
Your child’s CF team might suggest screening before the age of 10 years if they feel there is a reason to check for high blood glucose levels. These reasons could include the following in your child:
- passing a lot of urine, feeling thirsty and drinking a lot
- poor weight gain or slowed height growth
- unexplained weight loss
- a decline in lung function or more frequent infections without an obvious explanation.
Why screen for CFD?
Early diagnosis and treatment of CFD has a positive impact on health. If untreated, high blood glucose levels from CFD can cause long-term complications. Complications can be avoided by diagnosing CFD early and getting high glucose levels under control.
How is CFD treated?
Although CFD can’t be cured, it can be treated and managed very successfully. Your CF team will give you advice about treatment that is specific to you and your dietary and clinical needs. The aim of treatment is to reduce high blood glucose levels and keep these levels within the normal range as much as possible. The main treatments for CFD are dietary changes and insulin therapy.
Dietary changes aim to improve blood glucose control whilst making sure your nutritional and health needs are met. Your CF dietitian will give you specific dietary advice to meet your current needs. This means that some people with CFD may receive different dietary advice to other people with CFD, and to people with diabetes who don’t have CF. Carbohydrates are your body’s main source of energy and everyone needs carbohydrates in their diet. If you have CFD, you will need to pay attention to when and how many carbohydrates you are eating. This is because carbohydrates are broken down into glucose, so have the biggest effect on your blood glucose levels. Balancing your dietary carbohydrate, exercise, and your medical treatment are key to keeping your blood glucose levels under control. Read more about carbohydrates and diabetes.
If you need insulin, your CF team will advise you on an insulin regimen to meet your needs. They will teach you how to take insulin and give you the support you need.
Some people will be able to manage their CFD with dietary changes and oral medication. Your CF team will assess if this is the case for you.
If you are diagnosed with CFD and start treatment for this, you are eligible for free prescriptions and you should complete a prescription charge exemption application. Speak to your doctor about how to apply. Read more about prescription charges for people with CF.
Monitoring blood glucose levels
Your CF team will advise you how often and when you should be checking your blood glucose levels. Blood glucose levels can be monitored by pricking your finger and using a blood glucose meter or by wearing a continuous glucose monitor (CGM) such as FreeStyle Libre® or Dexcom®. A CGM device can reduce the need for regular finger prick tests. Normal blood glucose levels are generally between 4–10mmol/l, but this may vary and your CF team will recommend blood glucose targets for you. Your CF team will tell you what to do if your blood glucose levels are too low (hypoglycaemia) or too high (hyperglycaemia).
You should check your blood glucose levels as directed by your CF team or diabetic team but the following are general guidelines:
- Vary the times when you check your blood glucose levels so that over a week you’ll get a full picture.
- Blood glucose levels are best taken before meals, 1½-2 hours after meals, and before, after and once during overnight tube feeds (vary the time).
- Check your blood glucose levels more often if you are unwell.
- Check your blood glucose levels if you feel strange, unwell or are having a hypoglycaemic event (hypo).
- Check your blood glucose levels before and after strenuous exercise.
- Check your blood glucose levels before bed if you have had alcohol.
- Remember to record your result in a diary and to take your diary to all clinic appointments.
What is hypoglycaemia?
Hypoglycaemia, also known as a ‘hypo’, happens when blood glucose levels drop below 4mmol/l. Low blood sugar can feel different for different people. Symptoms might include:
- trembling or shaking
- a fast pulse or heart palpitations
- mouth or fingers feeling tingly
- difficulty concentrating and confusion
- blurred vision
- turning pale
- feeling anxious, irritable or tearful.
It is important to be able to recognise when your blood sugar is too low so you can treat it quickly.
How do I treat a hypo?
If you are not sure whether you feel hypo, check your blood glucose levels. When you feel a hypo coming on, you should:
- Stop what you are doing. If you feel able, check your blood glucose level.
- Immediately take a form of pure fast-acting sugar. The amount of sugar needed depends on your size, the type of insulin and how recently you have taken insulin, but 15g to 20g is usually sufficient. You can get this from: 100–200ml full sugar cola or lemonade (100mls for children); 3–4 teaspoons of sugar dissolved in water; 4–5 GlucoTabs® (3 tablets for children); 5–7 Lucozade Energy® tablets (3 tablets for children); 5–7 Dextro Energy® tablets (3 tablets for children); 1 ½–2 tubes of GlucoGel® or Dextrogel®. Chocolate is not recommended as it takes the body longer to digest lactose, which is the sugar present in chocolate.
- Sit down and relax. After 10–15 minutes, wash your hands and check your blood glucose level.
- If your blood glucose level is above 4mmol/L, follow up with a starchy, carbohydrate-containing snack such as a sandwich, milk and biscuits as this will help to maintain your blood glucose level and prevent another hypo.
- If your blood glucose level is still below 4mmol/L repeat this process until your blood glucose level is above 4mmol/L.
- Try not to over-treat your hypo, as this will result in high blood glucose levels.
What is hyperglycaemia?
Hyperglycaemia is a blood glucose level of above 14mmol/L. Some people with CFD will experience symptoms of high blood glucose levels, which can include:
- passing a lot of urine
- pins and needles
- hot sweats
- blurred vision
- weight loss.
Other people do not experience symptoms even if their blood sugar levels are very high. Some of the symptoms of hyperglycaemia are similar to some of the symptoms of hypoglycaemia so checking your blood glucose levels is important. Your CF team will tell you how to treat hyperglycaemia.
Annual review for complications
Having high blood glucose levels over a long period of time is usually linked to complications. This is because it can damage blood vessels and nerves in the body. You can avoid complications by diagnosing CFD early, getting high glucose levels under control, and having regular checks for signs of complications. If you have CFD, you will have a yearly diabetes review for signs of complications. This may be with your GP, local CFD specialists, or CF team.
The diabetes annual review will usually include:
- review of your recent clinical history, such as respiratory and gastrointestinal health
- dietary review
- lung function
- blood measure measurement
- blood tests for fat in the blood, chemicals that affect heart rhythm, kidney function, liver function, and blood glucose levels
- urine test for kidney function
- review of blood glucose levels
- review of diabetes treatment, such as your insulin doses, injection sites and techniques
- referral to local retinopathy service for eye screening
- foot examination
- review of wellbeing.
Illness and CFD
It is important to understand the effects of illness on your CFD and to know what you should do if you become unwell and/or are unable to tolerate food and fluids.
- The first sign of a chest infection or illness may be that your blood glucose levels are higher than usual. This is quite normal and you may temporarily need more insulin or tablets. Discuss this with your CF team.
- If you are unable to eat regularly, your blood glucose levels may be lower than normal.
- If you are unwell, you should check your blood glucose levels very regularly (every four to six hours) and to record them in your monitoring diary.
- Continue your usual treatment unless you are advised to change it by your CF or diabetes team, or if your blood glucose levels are very low.
- If you are unable to tolerate solid food it is important to take an alternative, such as a drink or snack like Lucozade, milk, fruit juice, fizzy drinks (not diet), ice cream, soup or supplement drinks, every two to three hours.
- To prevent dehydration it is also important to take some fluids that do not contain carbohydrate, such as water or sugar-free drinks.
- If you are vomiting, have diarrhoea, or your blood glucose levels are too high or too low, or if you are worried about any of these things, contact your CF team.
Driving and CFD
If you have diabetes that is treated with insulin or some oral medications, you need to tell the Driver and Vehicle Licensing Agency (DVLA) and your motor insurance provider. If you live in Northern Ireland, it’s the Driver & Vehicle Agency (DVA). Read more about driving when you have diabetes.
Exercise and CFD
Exercise is important for your health and wellbeing. During exercise, your body uses up glucose for energy. How exercise affects your blood glucose levels will depend on the type of exercise you’re doing and how long you’re doing it for. You should discuss your exercise plans with your CF team.
Alcohol and CFD
Pregnancy and CFD
Planning for pregnancy is very important when you have diabetes to reduce the risk of complications. Please talk to your CF team if you are thinking about getting pregnant. If you are pregnant and have CF, it is recommended that you monitor your blood glucose levels during each trimester or continuously if you already have confirmed diabetes. Please discuss this more with your CF and obstetric teams who will be able to arrange this with you. The following blood glucose targets are recommended for pregnant women with any form of diabetes:
- Fasting: below 5.3 mmol/l
- 1 hour after meals: below 7.8 mmol/l
Pregnant women with diabetes are also advised to take folic acid (5 mg/day) until 12 weeks of gestation.
Read more about planning for a pregnancy when you have diabetes.
CFD and travelling abroad
Planning your holiday is always exciting. If you have CFD it is important that you plan your holidays carefully. When travelling, remember:
- Talk to your CF team or diabetes nurse if you are unsure about diet or how different time zones might affect your treatments while you are on holiday.
- Check with your CF team whether you need to take salt tablets.
- Take out appropriate medical insurance that covers both your CF and your CFD. Ask your diabetes team for a customs letter to enable you to take any supplies easily through customs.
- Depending on how your CFD is treated, check you have enough insulin or tablets and equipment for the duration of the trip. Always take spares in case of breakage, ideally double the amount of supplies that you usually use for the duration of your holiday.
- Carry all equipment in your hand luggage, such as insulin syringes, insulin pens, blood glucose monitoring equipment, glucose tablets, your treatment record (e.g. your Insulin Passport), insulin or tablets.
- Ask our helpline (contact details on the back page) to organise a travel medication letter for you. This letter can be translated into several common holiday destination languages and explains why you are carrying your medications.
- Insulate your insulin in a cool bag whilst travelling and keep it away from direct light. Store insulin in a cool place when you arrive.
- Carry extra snacks and drinks for the journey.
- Make sure you drink plenty of low-sugar fluids, such as water and diet drinks, especially in hot countries.
- Be aware that certain types of airport security screening, such as X-ray machines, can damage insulin pumps and CGM devices. Ask airport security staff for safe security screening options. Read more in the position statement written by Diabetes UK.
If you or your child are diagnosed with CFD it might come as a shock. You may have new treatments to learn. Your CF team understands this may be a time of uncertainty and adjustment. They are there to assist you and provide any support you may need.
Many people can find aspects of managing CFD emotionally challenging. Reach out to your CF team, including your CF psychologist if available, if you are struggling.
Find out more
Check out our CFD factsheet. You can also find out more about our Strategic Research Centre investigating CFD.
CF diabetes information
Find out more about diabetes and why it can be associated with CF.
Page last reviewed: January 2024
Next review due: January 2026
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