CF diabetes

Cystic fibrosis diabetes (CFD) is a common complication of cystic fibrosis (CF). It causes a person’s blood sugar (glucose) levels to become too high. The amount of glucose in your blood is controlled by insulin, which is produced by the pancreas. In most people with CF, the pancreas doesn’t work properly. This can cause two important medical issues.  

Firstly, the pancreas can’t produce enough digestive enzymes that break down food. This is why most people with CF have to take pancreatic enzyme replacement therapy (Creon®) with food and snacks containing fat. Secondly, the pancreas can reduce, or stop, insulin production. This can lead to CFD.

Cystic fibrosis diabetes is common in adults and young people with CF. Data from the UK CF Registry 2021 indicates that more than one-third of people with CF aged 16 and over are being treated for CFD and 8% of children aged 10–15 with CF are being treated for CFD.

There are two main types of diabetes in the general population: type 1 and type 2 diabetes. Cystic fibrosis diabetes is distinct from type 1 and type 2 diabetes. It has features of both, but is different in what causes it, how it can present, and how it is screened for and treated. It is possible for someone with CF to get type 1 or type 2 diabetes.

For people with CF, glucose levels can also be influenced by infection, nutrition, liver function, and drugs such as steroids or immunosuppressants. These factors are important in the diagnosis and treatment of CFD. In some cases, an episode of CFD or high blood glucose levels may resolve itself when the infection is treated or the drugs are reduced or stopped.

Regular screening for CFD means that many people are diagnosed before they experience any symptoms. In others, the signs and symptoms may include:

• weight loss
• reduced lung function
• increased thirst
• the need to pass urine more frequently
• feeling weak or tired
• blurred vision.

If untreated, high blood glucose levels from CFD can cause long-term complications. These include kidney damage, problems with eyesight, nerve damage, problems with stomach emptying, high blood pressure, and high cholesterol. If you have CFD, you will have a yearly review to check for signs of complications and treat these where necessary. Complications can be avoided by diagnosing CFD early and getting high glucose levels under control.

Screening for CFD is important to diagnose and treat CFD early and avoid long-term complications. There are different methods for screening for CFD. These include:

• serial blood glucose monitoring or continuous glucose monitoring (CGM)
• oral glucose tolerance test (OGTT)

There are other screening tools that can measure blood glucose, but not all are effective for CFD. If screening shows your blood glucose levels are high, you might have further assessments to decide whether treatment is needed.

Although CFD can’t be cured, it can be treated and managed very successfully. The main treatments for CFD are insulin and dietary changes. The aim of treatment is to keep blood glucose levels within a normal range. This will help to maintain good nutrition, growth, and lung function, and prevent long-term complications.

Insulin is usually taken as an injection rather than a tablet, because it is destroyed by acid in the stomach. If you are taking insulin, you will need to regularly test your blood glucose levels. Your CF Team will tell you how to do this, when to test, and how often to test. They will also tell you what to do if your blood glucose levels are too low (hypoglycaemia) or too high (hyperglycaemia).

For people with CF on insulin treatment, NHS England offer a wearable sensor that relays glucose levels to a smart phone or e-reader, called the Freestyle Libre Flash Glucose Monitoring Sensor. This can reduce the need for inconvenient and sometimes painful finger prick blood tests to measure glucose levels. The device is the size of a £2 coin and sits on the arm. Speak to your CF Team to find out if you might be eligible for this device.

If you have CFD, your diet may also be adjusted to help control your blood glucose levels and make sure you are meeting your nutritional requirements. Your insulin dose may need to be adjusted to dietary changes. 

Download our CFD factsheet to find out more about how CFD is treated.

Our CFD factsheet covers everything from how you might feel after you are diagnosed with CFD to guidelines about treating the condition and how to adapt your diet. You can also find out more about our Strategic Research Centre investigating CFRD.