Metabolic syndrome prevalence varies significantly based on the specific diagnostic criteria and waist thresholds usedDifferent Diagnostic Rules Change How Metabolic Syndrome Is Identified

IntroductionThe prevalence of metabolic syndrome (MetS) is difficult to define because there is no universal consensus on the definition of MetS and similarities and differences in definitions of the components and the architecture of the definitions can significantly affect the prevalence and individual classification. The aim of this systematic review was to assess the impact of alternative definitions of MetS on prevalence, diagnostic agreement, reclassification, metabolic components and ethnicity-specific classification.MethodsA systematic review was carried out following the PRISMA 2020 guidelines. Studies met inclusion criteria if they included a comparison of 2 or more MetS diagnostic definitions in the same adult population. Information was gathered about study characteristics, diagnostic frameworks, thresholds for the components of MetS, prevalence of MetS, agreement between the two diagnostic methods, reclassification, and regional or ethnic specific criteria. A descriptive synthesis of finding was completed because of the significant degree of population and diagnostic heterogeneity. ResultsNine studies were included in the evidence synthesis. The prevalence of MetS was highly heterogeneous when the same population was assessed using different diagnostic criteria. The prevalence rates in Finnish adults ranged from 17.7% (WHO criteria) to 43.0% (JIS criteria), and the prevalence rates in the nationwide Iranian study ranged from 32.0% (IDF criteria) to 47.6% (JIS criteria). There was high diagnostic concordance between structurally similar definitions such as between IDF versus JIS in Finland (κ = 0.97) while lower levels of concordance were found between comparisons using WHO criteria. The most frequently reported factors associated with diagnostic discordance were central obesity and waist circumference. In addition, there were significant variations in prevalence of MetS depending on the region-specific adjustment of waist-circumference thresholds. Furthermore, the prevalence of MetS varied significantly by region-specific adjustment of waist circumference thresholds. DiscussionThe prevalence of MetS from one diagnostic framework to another may not be directly comparable since it is highly definition-dependent. Waist thresholds may vary by ethnicity and this can be a significant factor in classification. Further research should include precise diagnostic criteria and thresholds, cross-classification data and validation of alternative definitions with clinically relevant outcomes.