Cystic fibrosis (CF) is a heritable disease caused by mutations in a gene called CFTR, which encodes for a transport protein that regulates the movement of water and salts in and out of cells. Mutations in the CFTR gene results in the transport protein being made incorrectly or not at all, which ultimately leads to the production of thick, sticky mucus in various organs and tissues.
While the most well-known symptoms of CF are centered in the lungs, nearly half of affected adults will develop diabetes as a result of the disease. This kind of diabetes is called CF-related diabetes, or CFRD.
What is diabetes?
Diabetes occurs when levels of glucose in the blood, commonly called blood sugar, are too high. The most common forms of diabetes are type 1 and type 2.
Type 1 diabetes is normally caused by the immune system mistakenly attacking the cells in the pancreas that secrete a hormone called insulin. This hormone helps cells to absorb glucose from the blood so they can use it for energy. As such, when insulin levels are too low, the cells cannot effectively absorb glucose from the bloodstream, so blood sugar levels get too high.
In type 2 diabetes, the pancreas makes lower-than-normal amounts of insulin, and the body’s tissues don’t respond to the hormone normally. This is called “insulin resistance.”
What is CF-related diabetes?
CFRD shares some traits with type 1 and type 2 diabetes. The sticky, thick mucus seen in CF damages the pancreas, leading to insufficient insulin production, much like in type 1 diabetes. The pancreas continues to produce insulin, but not enough to stay healthy.
In addition, people with CF are often insulin-resistant, a hallmark of type 2 diabetes. Insulin resistance in CFRD can be especially evident during an illness, pregnancy, or when using steroid medications.
What are symptoms of CFRD?
Common CFRD symptoms include increased thirst and excessive urination, both of which result from abnormally high blood sugar levels. CFRD may also cause excessive fatigue, weight loss, and an unexplained decline in lung function.
How is CFRD diagnosed?
Most CFRD patients do not know they have diabetes until the disease is diagnosed. For this reason, CF care guidelines for CFRD recommend that people with CF undergo an oral glucose tolerance test every year starting at age 10.
The recommended test is the oral glucose tolerance test. Another used sometimes to check for diabetes, called hemoglobin A1c, is not recommended for CFRD because it’s prone to false-negatives.
How is CFRD treated?
CFRD treatment includes monitoring blood sugar levels and keeping these levels within the normal range — usually with insulin injections — maintaining an active lifestyle, and eating healthy foods. Unlike people with type 1 and 2 diabetes, most CFRD patients need to eat a high-calorie diet to maintain a healthy body weight, as is the case with other CF patients.
The different types of insulin are classified by how long they last in the body and how fast they work. A patient and their care team should work together to determine the most suitable kind of treatment since no specific insulin regimen has been found to be better overall for CFRD.
Oral hypoglycemics, or anti-diabetic therapies, are not as effective as insulin to treat CFRD, and are not recommended outside the context of clinical trials.
Last updated: Sept. 1, 2021
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