What is diabetes?

Diabetes mellitus represents a set of autoimmune, metabolic and genetic disorders that share one major characteristic – hyperglycaemia. The recommended way of measuring plasma glucose and the threshold used to define what is normal or abnormal have gone through several iterations over the past few decades. These recommendations, and the current definitions of diabetes mellitus and intermediate states of hyperglycaemia, are reviewed here. Differences in approach between the USA and other parts of the world are highlighted.