The World Health Organization (WHO) have a classification system as defined below:
Type 1 Diabetes.
This is due to beta cell destruction, most often recognized as being caused by autoimmune disease. This means it is caused by an attack by the person’s own immune system. No food or lifestyle factor has been confirmed as a cause for Type 1 diabetes.
Type 2 Diabetes.
This is due to reduced pancreatic insulin secretion and reduced insulin action (insulin resistance). Not all Type 2 diabetes patients are the same and the ratio between the two defects can be very different in different communities. There can be a very strong family link but Type 2 diabetes is also linked to weight, not taking enough exercise These factors are often enough to tip the balance and cause diabetes in a susceptible person. This is because the person becomes resistant to the action of insulin, the pancreas then has to work harder and harder before eventually giving up. Diabetes then presents itself with high blood glucose at that time even though the signs of insulin resistance have been present for many years.
Hybrid forms of Diabetes.
These include a slowly evolving form of immune mediated diabetes where the person is initially thought to have Type 2 diabetes but who has evidence of positive pancreatic auto anti bodies just like in Type 1 diabetes. This is often referred to as latent auto immune diabetes in adults (LADA). This group of hybrid diabetes also includes ketosis prone Type 2 diabetes.
Other Types of Diabetes.
This includes diabetes secondary to pancreatic inflammation such as occurs in pancreatitis. Common risk factors for pancreatitis include chronic alcohol misuse and gallstones. This diverse group of diabetes causes includes insulin resistance states such as occurs when taking corticosteroids. It also includes a variety of genetic based disorders that present with high blood sugar levels. It is well worth thinking about different genetic causes at the time of diagnosis because some forms are exquisitely sensitive to oral drugs rather than insulin injections. No doubt with time this group of diabetes will become more defined and reclassified.
Hyperglycaemia first detected during pregnancy.
This group includes gestational diabetes, defined by newly recommended glucose cut off points that are lower than for diabetes. The group also includes diabetes mellitus which presents itself during pregnancy and is defined by the same criteria as in non-pregnant persons.
At the time of first diagnosis it may not be possible to say whether the diabetes is Type 1 or Type 2. There may not be sufficient markers to be sure at this point in time and only time will tell how the disease will develop. In this case the diabetes is classified as undefined.