Diagnosis of the metabolic syndrome: which definition should we use?

is a clustering of interrelated risk factors that identify individuals at increased risk for type 2 diabetes mellitus and cardiovascular disease. Insulin resistance is believed to be the major underlying metabolic abnormality. The incidence of the MetSyn increases with age, affecting more than 40% of those older than 60 years in the United States. About a quarter of the adult population of the United States has the MetSyn, representing about 47 million Americans. Data from the ATTICA and the METS-GREECE studies showed similar results in the Greek population. As already stated, the presence of the MetSyn predicts a greater risk for events related to cardiovascular disease and increased all-cause mortality. The National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) identified the components of the MetSyn that relate to cardiovascular disease (Table 1) and considered the “obesity epidemic” as mainly responsible for the rising prevalence of the MetSyn. Furthermore, Met Syn increases the risk of type 2 diabetes mellitus, which in turn is a major risk factor for atherosclerotic disease. The MetSyn is also associated with a variety of other conditions (Table 2). The NCEP ATP III guidelines define the MetSyn as a new secondary target for cardiovascular disease risk reduction therapy beyond low-density lipoprotein cholesterol (LDL-C) lowering. It follows that the diagnosis of the MetSyn is very important. But how can we reach a diagnosis of the MetSyn? At least 5 organisations have recommended clinical criteria for the diagnosis of the MetSyn. These criteria are similar in many aspects, but they reveal fundamental differences concerning the predominant causes of the MetSyn and the definition of obesity. In 1998, a World Health Organisation (WHO) group proposed a definition for the MetSyn (Table 3). A potential disadvantage of the WHO criteria is the fact that, at least in some cases, special laboratory tests beyond routine assessment might be needed. In 1999, the European Group for the study of Insulin Resistance (EGIR) proposed its own criteria for the diagnosis of the MetSyn (Table 4). The WHO and the EGIR definitions agree in that they both include either glucose intolerance or insulin resistance as an essential component. The American Association of Clinical Endocrinologists proposed another set of criteria for the MetSyn (Table 5). Obesity is not included in these criteria. A major disadvantage of this definition is that the number of risk factors needed for the diagnosis of the MetSyn is not specified, leaving the diagnosis to the health care provider’s judgement. The most applicable set of criteria in everyday clinical practice is that of the NCEP