Most people are familiar with type 1 and type 2 diabetes. Recently, though, a new type of diabetes has been identified: type 3c diabetes.
Type 1 diabetes is where the body’s immune system destroys the insulin producing cells of the pancreas. It usually starts in childhood or early adulthood and almost always needs insulin treatment. Type 2 diabetes occurs when the pancreas can’t keep up with the insulin demand of the body. It is often associated with being overweight or obese and usually starts in middle or old age, although the age of onset is decreasing.
Type 3c diabetes is caused by damage to the pancreas from inflammation of the pancreas (pancreatitis), tumours of the pancreas, or pancreatic surgery. This type of damage to the pancreas not only impairs the organ’s ability to produce insulin but also to produce the proteins needed to digest food (digestive enzymes) and other hormones.
However, our latest study has revealed that most cases of type 3c diabetes are being wrongly diagnosed as type 2 diabetes. Only 3% of the people in our sample – of more than 2m – were correctly identified as having type 3c diabetes.
Small studies in specialist centres have found that most people with type 3c diabetes need insulin and, unlike with other diabetes types, can also benefit from taking digestive enzymes with food. These are taken as a tablet with meals and snacks.
Researchers and specialist doctors have recently become concerned that type 3c diabetes might be much more common than previously thought and that many cases are not being correctly identified. For this reason, we performed the first large scale population study to try and find out how common type 3c diabetes is.
We also looked into how well people with this type of diabetes have their blood sugar controlled. To do this we analysed health records from over 2m people in England. The records used were taken from the Royal College of General Practitioners Research and Surveillance Database (RCGP RSC). This database, mainly used for flu surveillance, contains the anonymised healthcare records of people of all ages for a sample of GP practices spread out across England.
We looked for cases of diabetes occurring after conditions which had caused damage to the pancreas including pancreatitis, pancreatic cancer and tumours, and pancreatic surgery. These cases of diabetes are likely to be cases of type 3c diabetes. The proportion of people with diseases of the pancreas who go on to develop diabetes is not clear but it does not happen in all cases, and there may be a long delay before the onset of diabetes.
To our surprise, we found that in adults, type 3c diabetes was more common than type 1 diabetes. We found that 1% of new cases of diabetes in adults were type 1 diabetes compared with 1.6% for type 3c diabetes.
People with type 3c diabetes were twice as likely to have poor blood sugar control than those with type 2 diabetes. They were also five to ten times more likely to need insulin, depending on their type of pancreas disease.
We found that the onset of type 3c diabetes could occur long after the onset of pancreas injury. In many cases more than a decade later. This long lag may be one of the reasons the two events are not often thought of as being linked, and the diagnosis of type 3c diabetes is being overlooked.
Correctly identifying the type of diabetes is important as it helps the selection of the correct treatment. Several drugs used for type 2 diabetes, such as gliclazide, may not be as effective in type 3c diabetes. Misdiagnosis, therefore, can waste time and money attempting ineffective treatments while exposing the patient to high blood sugar levels.
Our findings highlight the urgent need for improved recognition and diagnosis of this surprisingly common type of diabetes.
Andrew McGovern has previously received funding from the Wellcome Trust, Eli Lilly, and AstraZeneca for research.