Cystic fibrosis related diabetes

Cystic fibrosis related diabetes (CFRD) is different to other types of diabetes. CFRD is caused by the build up of thick secretions in the pancreas. These secretions damage the cells that produce a hormone called insulin.

Insulin normally helps take glucose from the blood to the cells of the body.

When the insulin does not work as it normally should, it can cause blood glucose levels to go too high and this can sometimes be followed by low blood glucose levels. This is called rebound hypoglycaemia.

Symptoms of hypoglycaemia include dizziness, feeling shaky, sweaty or hungry or looking pale. A lack of insulin causes the blood glucose levels to rise. High blood glucose levels can lead to symptoms such as poor weight gain, tiredness and reduced lung function. These high levels can also increase the risk of infection.

CFRD is diagnosed by an oral glucose tolerance test (OGTT). This test tells us how well the body can cope with a high glucose intake. If a child’s OGTT is abnormal, they may need to wear a continuous blood glucose monitoring system (CGMS). This device is worn under the skin and measures blood glucose levels every five minutes for seven days.

CFRD is treated with insulin alongside some changes to food and drink intake.

Treatment aims to keep blood glucose levels between 4 and 10mmol/l.

Insulin is used to achieve stable blood glucose levels by helping glucose leave the blood and enter the cells where it can be used for energy. The dose of insulin given can be adjusted according to the amount of carbohydrate eaten.

There are three main food groups: carbohydrate, protein and fat.

Carbohydrate is a term for both starch and sugar (glucose) and it is the only food group that directly affects blood glucose levels.

Fat and protein have very little effect on blood glucose levels.

Carbohydrate foods are digested and absorbed into the blood at different rates. Sugary foods will be broken down into glucose and absorbed quickly and so cause blood glucose levels to rise quickly.

Examples of sugary foods:

• jelly sweets

• non-diet fizzy drinks

• honey

• syrup

• rice

• pasta

• chapatti

• potato

• bread

• breakfast cereals

It is important to eat regular meals and snacks, including starchy carbohydrates, protein and fat. This will ensure we get enough energy and nutrients to maintain a healthy body weight.

People should avoid any drinks that contain sugar such as fizzy drinks and squashes. You should also avoid sugary sweets. Fruit juice contains a lot of fruit sugar so should only be taken in small quantities with a meal.

Milk and milkshakes are a good source of energy (calories) and calcium. It is okay to continue to include these as part of your diet. All sugar-free drinks are suitable.

It is important that people continue to eat plenty of starchy carbohydrate foods as part of their meals. These foods are a good energy source and provide important nutrients. Try to include them at each meal.

If people currently have food or drink between meals then they should continue to do so.

Hypo is a blood glucose level of less than 4.0mmol/L. Symptoms of hypo include dizziness, feeling shaky, sweaty or hungry or looking pale. Hypo should be treated with 15g fast acting carbohydrate. Some examples are in the table below:

Fast acting carbohydrates

Once treated, wait 15 minutes and then the blood glucose level should be re-checked. If it is still less than 4.0mmol/l then re-treat.

If blood glucose has increased have 15-20g of slow-acting carbohydrate to prevent levels from dropping again.

Slow-acting carbohydrates

Yes. If high-calorie supplement drinks are taken, people should continue to do so as these provide the extra calories needed. They do contain some carbohydrate but are suitable for those with CFRD, and should be discussed with a specialist dietitian.

Usually overnight feeds are given over several hours so the carbohydrate is broken down gradually and the glucose is absorbed slowly. There is a long-acting insulin that is also absorbed slowly that can help control blood glucose overnight. A specialist diabetes team can advise how to manage a regimen.

There are very few foods that should be avoided completely. People should, however, avoid sugary sweets and sugar-containing drinks unless treating a hypo. These drinks contain pure sugar which requires very little digestion so is absorbed very quickly and can cause blood glucose to rise rapidly.

Diabetic products are available but are not recommended. They contain sugar alcohols which, if eaten in large quantities, can have a laxative effect. They are also expensive.

Yes, they need to continue to take enzymes as advised. If they are eating extra fatty foods they may need to increase the enzyme dose to prevent malabsorption.