Basis of the present classification of diabetes.

The present classification of diabetes most widely used is that recommended by the National Diabetes Data Group and subsequently endorsed by the World Health Organization. This classification is primarily a clinical classification of diabetes because in most instances the etiology is unknown. The need for a standardized classification arose out of the recognition that diabetes was a syndrome rather than a single disease and the different terminologies which emerged. While certain types of diabetes can be classified according to specific etiology or associations with specific syndromes, the vast majority cannot. Insulin-dependent and noninsulin-dependent diabetes usually represent syndromes whose etiopathology is believed to differ and their clinical characteristics are usually distinctive. As evidence of etiological heterogeneity has increased there has been a tendency to adopt the terms Type I and Type II diabetes to indicate different etiologies, although the original usage of these terms was as a clinical classification to differentiate between insulin dependent and non-insulin-dependent disease. At present the use of the four terms to describe the common types of diabetes leads to confusion, which could readily be resolved by arriving at agreed definitions for each of these terms. While the NDDG-WHO classification has served to standardize terminology and stimulate research into the different causes of diabetes, some further refinement of the classification, together with some additional definition of terms, should be considered. The classification of diabetes most widely used at the present time is that suggested by the National Diabetes Data Group (NDDG) in the United States in 1979, which was subsequently recommended by the World Health Organization (WHO) Expert Committee on Diabetes Mellitus in 1980. It should be stressed that this classification was intended to be a uniform framework for clinical and epidemiological research, and that the classification would almost certainly have to be modified on the basis of new knowledge in the future.