Types of Diabetes

As well as revising the diagnostic criteria for diabetes, the ADA also proposed changes of name for the two main forms of the syndrome and these terms are now in general use. Hence the former Insulin-Dependent Diabetes Mellitus or IDDM may now be called type 1 diabetes and Non-Insulin Dependent Diabetes Mellitus (NIDDM) may be termed type 2 diabetes. On a worldwide basis, Type 2 diabetes accounts for over 85 per cent of cases, although incidence varies between different ethnic groups. In the UK, more than 1.4 million people are known to have diabetes and about 80 per cent of this is Type 2. As previously noted, diabetes is a complex series of disorders which, to a certain extent, refuses to be slotted neatly into categories. Part of the problem is that diabetic conditions may change with time. The following sections identify relevant states and syndromes, as well as the categories of diabetes that are recognized, with a brief description of each.

Impaired Fasting Glucose (IFG)

IFG is a state which is most accurately identified by means of the Oral Glucose Tolerance Test described above. It is considered to be an intermediate state, falling short of diabetes, but maybe a pre-diabetic stage in some cases. It is identified when an abnormally high level of fasting glucose of 6.1 to 6.9 mmol/1 is obtained from a venous plasma sample before the glucose drink is given, but a normal reading, of less than 7.8 mmol/1, exists after 120 minutes. (In normality, the fasting glucose level is at, or less than, 6.0 mmol/1.) IFG does not usually produce symptoms and the clinical implications are not, at present, fully established. A person identified with this condition may receive advice on diet, if appropriate, and further monitoring of blood glucose levels so that any changes can be identified.

Impaired Glucose Tolerance (IGT)

IGT is a second intermediate state, falling in between normality and diabetes and is one which can only be diagnosed by means of the OGGT. For IGT to exist, an abnormally high reading for fasting glucose, of 6.1 to 6.9 mmol/1, is obtained from a venous plasma sample, as in IFG. However, 120 minutes into the test, after the glucose drink has been taken, the reading remains abnormally high in the second plasma sample, at 7.8 to 11.0 mmol/1. This distinguishes IGT form both IFG and normality, in which the second reading is less than 7.8 mmol/1, and from diabetes, in which it is greater than 11.1 mmol/1. People with IGT usually do not have any symptoms but they may eventually develop Type 2 diabetes (2 to 5 per cent of those diagnosed). However, IGT can also be transitory (for example it can develop during pregnancy: see gestational diabetes) and some people return to normal levels of glucose tolerance with the passage of time. Defects in insulin receptors may be the cause of IGT in some cases and this may be reversible with treatment. Those with long-term, stable IGT are considered to be at greater risk both of Type 2 diabetes and also of the microvascular complications of the syndrome (such as heart disease, stroke, and conditions affecting the circulation in the legs).

It is quite common for IGT (or Type 2 diabetes) to be diagnosed after a person has developed macrovascular disease, with this being the presenting condition for which the person is receiving treatment. Also, sometimes a misdiagnosis of Type 2 diabetes is made when, in fact, the person has IGT People at a greater risk of heart disease, because of the existence of high blood pressure (hypertension), elevated levels of triglycerides, in blood plasma, high pulse rate and/or obesity, are also considered to be at high risk of IGT and/or Type 2 diabetes. In addition, the incidence of IGT is associated with ageing. IGT and IFT are similar, and more research is being carried out to establish the exact differences and long-term implications of these two states.

• Type 1 Diabetes
• Type 2 Diabetes
• Other forms of diabetes mellitus