Cystic Fibrosis Related Diabetes

  • In CFRD, the body doesn’t make enough insulin AND sometimes lacks the normal responses to insulin. The insulin deficiency is mainly due to the scars in the pancreas caused by the thick sticky mucus. The insulin resistance can come and go; it can be caused by high amounts of stress, an underlying infection, chronic inflammation, and use of steroids. This is why some patients only need to take insulin while they are in the hospital but not at home.
  • While years of high blood sugars can cause macrovascular issues such as high cholesterol, high blood pressure, and heart disease in the general population, this has not been seen in CF patients. However, they are at risk for microvascular issues, such as issues with their eyes, kidneys, and nerves.
  • There are two other issues that we also worry about with long standing hyperglycemia in CFRD.
  • One is the inability to gain or maintain weight. This is because the glucose is running around in the blood, not in the cells where it can be used for energy.
  • Long term hyperglycemia can also cause a decrease in lung function, as the sugars in the blood provide a breeding ground for infections in the lungs.
  • CF patients are also prone to having hypoglycemia (low blood sugar), but this is often not correlated with the development of CFRD.
  • All of these complications are why we have the nursing staff check blood sugars in the hospital, and why the Cystic Fibrosis Foundation recommends that patients do annual* Oral Glucose Tolerance testing (see OGTT section below for more details on this).
  • Treatment for CFRD is done using insulin.
    • We will put patients either on a daily dose of long acting insulin like Lantus, have them carb count at meals and cover their carbs with a rapid acting insulin like Novalog or Humalog, or both.
    • We do not have patients restrict carbohydrate intake, as this typically causes them to decrease their total caloric intake and lose weight.


Oral Glucose Tolerance Test (OGTT)

It’s crucial that you work with your CF team to get tested every year for cystic fibrosis-related diabetes (CFRD). Early diagnosis and treatment will improve your overall health, your nutritional status, your lung function and your survival.

The best way to diagnose CFRD is an oral glucose tolerance test (OGTT). This screening test is usually started at age 10 and done once a year when your health is stable (you are not sick). *We have a NEW protocol at the center that will allow patients to skip the OGTT if their A1c (average blood sugar over 3 months, taken via finger poke) is below 5.8.*

The OGTT is done in the morning. You’ll fast (no food or beverages, except water) for at least 8 hours beforehand. You should eat your usual diet for 3 days before the test.

You will be given a sweet beverage to drink containing a high carbohydrate load (high glucose; a lot of sugar) dissolved in water. Then you’ll sit or lie quietly for 2 hours. Your blood sugar will be measured before you drink the beverage and again 2 hours later.

Your CF team will make a diagnosis of CFRD when:

  • Your fasting blood glucose (sugar) is greater than or equal to 126 mg/dl on two separate days.
  • A blood glucose taken at any time of day is greater than or equal to 200 mg/dl and you have some warning signs listed in “Learn About CFRD.”
  • Your 2-hour OGTT blood glucose is greater than or equal to 200 mg/dl.
  • Other Times to Screen — When You’re Sick or Pregnant

Besides the yearly screening, CFRD can also be diagnosed if you become sick, are on IV antibiotics and/or are taking steroids, or are pregnant.

These conditions cause the body cells to become resistant to the action of insulin, not allowing it to be absorbed into the cell. This is called “insulin resistance.” Insulin resistance, combined with not enough insulin being made by the body, causes blood glucose to rise. CFRD may also be diagnosed when people with CF are on tube feedings.


Screenings When You Are Sick

When you are sick and in the hospital, your blood glucose is often checked for the first 48 hours after admission. It will be checked when you are fasting (before you eat) and 2 hours after you eat.

If you are sick and being treated at home, you should talk with your CF team members about checking your blood glucose with a blood glucose meter as instructed by your health care team. A diabetes diagnosis would have to be confirmed by a lab test at the hospital.


Screenings Related to Pregnancy

If you are planning on becoming pregnant, your CF team or your obstretrician may recommend an OGTT to rule out diabetes before getting pregnant.

If you should become pregnant and haven’t had an OGTT within the last 6 months, you should have an OGTT early in your pregnancy. If it is negative for diabetes, you should have another OGTT at 12 to 16 weeks and again at 24 to 28 weeks.

After delivery, you should have your blood glucose checked again within 6 to 12 weeks with an OGTT. Your obstetrician may be the one who orders these screening tests. If so, have the results — whether they are normal or abnormal — sent to your CF care team.

Other Times to Screen for CFRD

High blood glucose can also occur with the use of high-calorie tube feedings. It is recommended that people getting tube feedings have their blood glucose checked every so often either at home with a glucose meter, or while in the hospital during the tube feeding to screen for CFRD.

People without CFRD who are listed for a lung transplant and have not been screened for CFRD within the last 6 months should be screened.

Blood glucose should be monitored after transplant while in the hospital. After being discharged, people who have had a transplant should have regular screening every year for CFRD if they have no symptoms.

FAQs About Diagnosing CFRD

The HbA1c test is not a good screening test because it may miss people who have CFRD. The test is used in people with diabetes to follow how well they are doing with the management of their blood glucose.
A FBG finds people with CFRD who have high fasting blood sugars, but does not find people with CFRD who may have normal FBG but have very high blood glucose after eating. This is why an OGTT is recommended. It is the most accurate test for diagnosis of CFRD.

Other tests, such as fructosamine, urine glucose and random glucose levels, are not as accurate as an OGTT to test for CFRD.

A CGM is not a tool that can be used to diagnose diabetes. No studies have shown that a CGM can give your doctor the information needed to diagnose CFRD in the way that the OGTT does.