[Update on the diagnosis of diabetes].

Diabetes mellitus is a chronic metabolic disease characterized by the presence of hyperglycemia. This condition must be detected early in order to establish a proper treatment and prevent its micro and macro vascular complications. The diagnosis of diabetes mellitus is based on the detection of abnormally high levels of glycemia. This task may appear to be simple but should not be underestimated. Misclassifying an individual as a diabetic can expose him/her not only to emotional damage but also to unnecessary diagnostic tests and potentially harmful treatments. Many different clinical situations such as pregnancy or acute critical illness may hamper the interpretation of laboratory findings. In this article, we present an updated review on the main aspects related to diagnosis of diabetes mellitus.