Objective: New definitions proposed by the International Diabetes Federation (IDF) and by the modified National Cholesterol Education Program (NCEP) have caused some confusion in classifying patients as having metabolic syndrome because some patients satisfy the modified NCEP criteria but not the IDF criteria. This study was conducted to assess the agreement between the modified NCEP and IDF criteria and to identify the characteristics of the subjects who satisfy the modified NCEP criteria but not the IDF criteria.
Methods: A total of 1,068 individuals aged ≥ 20 years, who visited the Health promotion Center at One hospital from June 30th 2004 to January 20th 2005, were included in this study. Metabolic syndrome was defined according to the modified NCEP criteria and the IDF criteria. Participants who simultaneously satisfied both the modified NCEP and IDF criteria were classified into the metabolic syndrome group. Those diagnosed with metabolic syndrome according to the modified NCEP criteria but classified as syndrome-free according to the IDF criteria were assigned to the discrepant group; individuals classified as syndrome-free by both sets of criteria were assigned to the non-metabolic syndrome group.
Results: The discrepant group showed more adverse metabolic profiles and unfavorable lifestyles despite their lower body mass index and waist circumference compared to those identified as having metabolic syndrome by both the IDF and modified NCEP criteria. Insulin resistance such as HOMA-IR and McAuley index of the discrepant group was higher than those with no metabolic syndrome after adjusting age, smoking, alcohol and exercise.
Conclusions: The IDF criteria were inferior to the modified NCEP criteria in identifying the metabolically abnormal but physically normal weight groups, known to be predisposed to type 2 diabetes and coronary heart disease. Further research regarding the clinical significance of this discrepant group and the appropriateness of central obesity as an obligatory criterion in defining metabolic syndrome seems to be warranted.

Keywords: Insulin resistance, Metabolic syndrome, SGOT, Diagnostic criteria