[Diabetes mellitus: definition, classification and diagnosis].

Diabetes mellitus comprises of a group of heterogeneous disorders, which have an increase in blood glucose concentrations in common. The current classifications for diabetes mellitus type 1-4 are described and the main features of type 1 and type 2 diabetes are compared to allow for better discrimination between these diabetes types. Furthermore, the criteria for the correct biochemical diagnosis during fasting and oral glucose tolerance tests as well as the use of hemoglobin A1c (HbA1c) are summarized. These data form the basis of the recommendations of the Austrian Diabetes Association for the clinical praxis of diabetes treatment.