The term diabetes mellitus describes several diseases of abnormal carbohydrate metabolism that are characterized by hyperglycemia. It is associated with a relative or absolute impairment in insulin secretion, along with varying degrees of peripheral resistance to the action of insulin. Every few years, the diabetes community reevaluates the current recommendations for the classification, diagnosis, and screening of diabetes, reflecting new information from research and clinical practice.
The American Diabetes Association (ADA) issued diagnostic criteria for diabetes mellitus in 1997, with follow-up in 2003 and 2010 [1-3]. The diagnosis is based on one of four abnormalities: hemoglobin A1C (A1C), fasting plasma glucose (FPG), random elevated glucose with symptoms, or abnormal oral glucose tolerance test (OGTT) (table 1). Patients with impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT) are referred to as having increased risk for diabetes (see 'Diagnostic criteria' below).
Recommendations for routine screening for diabetes are provided elsewhere. The etiologic classification of diabetes mellitus is also discussed separately. (See "Screening for diabetes mellitus" and "Classification of diabetes mellitus and genetic diabetic syndromes".)
The 1997 ADA Expert Committee introduced the terms type 1 and type 2 diabetes, and recommended against terms like insulin-dependent, non-insulin-dependent, juvenile-onset, maturity-onset, and adult-onset diabetes . In addition to type 1 and type 2 diabetes, "specific types" of diabetes are identified: gestational diabetes, and diabetes secondary to recognized genetic defects, diseases of the exocrine pancreas, other endocrinopathies, or to drugs. This change was an attempt to classify diabetes according to etiologic differences rather than descriptions based upon age at onset or type of treatment.
The diagnosis of diabetes mellitus is easily established when a patient presents with classic symptoms of hyperglycemia (thirst, polyuria, weight loss, blurry vision) and has a random blood glucose value of 200 mg/dL (11.1 mmol/L) or higher, and confirmed on another occasion.