Fasting Plasma Glucose Outperforms Glycated Hemoglobin in Identifying Metabolic Syndrome: Evidence from a Population-based Cross-sectional Study in Rural Bangladesh

Aim and background: Metabolic syndrome (MS) is a key determinant of cardiovascular and type 2 diabetes mellitus (T2DM) risk, especially in South Asia, where insulin resistance and dyslipidemia are prevalent.This study aimed to determine whether glycated hemoglobin (HbA1c) could replace fasting plasma glucose (FPG) for identifying MS in a rural Bangladeshi population by directly comparing their diagnostic accuracy, clinical utility, and reclassification.Methods: This population-based cross-sectional study analyzed data from 2,112 adults aged 20 years from the Chandra cohort, collected in 2009 following WHO STEPS procedures.Individuals with known or newly detected diabetes were excluded.Metabolic syndrome was defined using the National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) criteria modified for South Asians.Anthropometric and biochemical measurements were obtained under strict internal and external quality control.Diagnostic accuracy was assessed using receiver operating characteristic (ROC) curves, decision-curve analysis, agreement statistics, and reclassification indices.Results: The prevalence of metabolic syndrome was 26.4%.Fasting plasma glucose demonstrated superior diagnostic performance compared with HbA1c, showing greater discriminative ability [area under the curve (AUC) 0.704 vs 0.636)], higher specificity (93.9 vs 80.3%), and stronger overall clinical utility across sex and body mass index subgroups.Decision-curve and spline analyses consistently indicated a higher net clinical benefit and a more linear association between FPG and metabolic risk.In contrast, HbA1c-based models tended to overestimate metabolic risk, reflecting lower specificity in this population and showing weaker diagnostic agreement ( = 0.21).Conclusion: Fasting plasma glucose is a more specific and context-appropriate marker for detecting MS in non-diabetic adults in rural South Asia, while HbA1c may overclassify risk.Clinical significance: (1) Fasting plasma glucose offers higher diagnostic precision and stability.(2) Glycated hemoglobin is prone to distortion from non-glycemic factors common in South Asia.(3) Fasting plasma glucose-based screening should be prioritized in resource-limited settings.