Since 1965 the World Health Organization (WHO) has published guidelines for the diagnosis and classification of diabetes. These were last reviewed in 1998 and were published as the guidelines for the Definition, Diagnosis and Classification of Diabetes Mellitus3. Since then more information relevant to the diagnosis of diabetes has become available.
In addition, in 2003, the ADA reviewed its diagnostic criteria4. While the criteria for the diagnosis of diabetes and Impaired Glucose Tolerance (IGT)remained unchanged, the ADA recommended lowering the threshold for Impaired Fasting Glucose (IFG) from 6.1mmol/l (110mg/dl) to 5.6mmol/l (100mg/dl) (. The Expert Committee on the Diagnosis and Classification of Diabetes
Mellitus, 2003). In view of these developments WHO and the International Diabetes Federation (IDF) decided that it was timely to review its existing guidelines for the definition and diagnosis of diabetes and intermediate hyperglycaemia.
Recent estimates indicate there were 171 million people in the world with diabetes in the year 2000 and this is projected to increase to 366 million by 20301.
Diabetes is a condition primarily defined by the level of hyperglycaemia giving rise to risk of microvascular damage (retinopathy, nephropathy and neuropathy). It is associated with reduced life expectancy, significant morbidity due to specific diabetes related microvascular complications, increased risk of macrovascular complications (ischaemic heart disease, stroke and peripheral vascular disease), and diminished quality of life. The American Diabetes Association (ADA) estimated the national costs of diabetes in the USA for 2002 to be $US 132 billion, increasing to $US 192 billion in 20202.
There are now many data available, and also much more aetiological information has appeared. It seemed timely to re–examine the issues and to update and refine both the Classification and the criteria, and to include a definition of the “Metabolic Syndrome”.
An American Diabetes Association (ADA) expert group was convened to discuss these issues. It published its recommendations in 1997 (The Expert Committee on the Diagnosis and Classification of Diabetes Mellitus, 1997). WHO convened a Consultation on the same subject in London, United Kingdom, in December 1996. In general, the ADA and WHO groups reached similar conclusions.
According to World Health Organization (WHO), diabetes mellitus can be defined as a metabolic disorder of multiple aetiology characterized by chronic hyperglycaemia with disturbances of carbohydrate, fat and protein metabolism resulting from defects in insulin secretion, insulin action, or both. The effects of diabetes mellitus include long–term damage, dysfunction and failure of various organs.
In its most severe forms, ketoacidosis or a non–ketotic hyperosmolar state may develop and lead to stupor, coma and, in absence of effective treatment, death.
Often symptoms are not severe, or may be absent, and consequently hyperglycaemia sufficient to cause pathological and functional changes may be present for a long time before the diagnosis is made.
The long–term effects of diabetes mellitus include progressive development of the specific complications of retinopathy with potential blindness, nephropathy that may lead to renal failure, and/or neuropathy with risk of foot ulcers, amputation, Charcot joints, and features of autonomic dysfunction, including sexual dysfunction. People with diabetes are at increased risk of cardiovascular, peripheral vascular and cerebrovascular disease.
For population studies of glucose intolerance and diabetes, individuals have been classified by their blood glucose concentration measured after an overnight fast and/or 2h after a 75 g oral glucose load. Since it may be difficult to be sure of the fasting state, and because of the strong correlation between fasting and 2–h values, epidemiological studies or diagnostic screening have in the past been restricted to the 2–h values only. Whilst this remains the single best choice, if it is not possible to perform the OGTT (e.g. for logistical or economic reasons), the fasting plasma glucose alone may be used for epidemiological purposes.
It has now been clearly shown, however, that some of the individuals identified by the new fasting values differ from those identified by 2–h post glucose challenge values (De Vegt et al., 1998). The latter include the elderly and those with less obesity, such as many Asian populations. On the other hand, middle-aged, more obese patients are more likely to have diagnostic fasting values (.DECODE Study Group, 1998). Overall population prevalence may or may not be found to differ when estimates using fasting and 2–h values are compared.
CLASSIFICATIONS OF DIABETES MELLITUS
Assigning a type of diabetes to an individual often depends on the circumstances present at the time of diagnosis, and many diabetic individuals do not easily fit into a single class.
For example, a person with gestational diabetes mellitus (GDM) may continue to be hyperglycemic after delivery and may be determined to have, in fact, type 2 diabetes. (The Expert Committee on the Diagnosis and Classification of Diabetes Mellitus, 2003)