**Background:** Metabolic syndrome (MS) is a cluster of cardiovascular risk factors including central obesity, dyslipidemia, hyperglycemia, and hypertension. Its prevalence is rising globally, including in Asia. Mongolia faces increasing mortality from non-communicable diseases, particularly cardiovascular disease, yet no established diagnostic definition for MS exists for the Mongolian population. This study compared three widely used definitions—NCEP ATP III, IDF, and JIS—to estimate MS prevalence in urban Mongolia and recommend a preferred definition.
**Methods:** A cross-sectional survey was conducted following the WHO STEPS Surveillance Manual. Multistage cluster sampling selected 52 family healthcare centers from Ulaanbaatar's eight districts, then 88 individuals aged ≥20 years were randomly selected per center. Of 4,515 urban residents approached (98.7% response rate), 2,076 underwent complete biochemical measurements. Data collection occurred December 2017–January 2018. Measurements followed standardized protocols: blood pressure (average of three readings after 10 min rest), waist circumference (midway between lowest rib and iliac crest), and fasting blood samples for HDL-C, triglycerides, and glucose (analyzed via ERBA-XL200 automated analyzer). MS was defined per NCEP ATP III (≥3 of 5 components), IDF (required elevated WC plus ≥2 other components), and JIS (≥3 of 5 components, with ethnicity-specific WC cutoffs). Asian thresholds were used for abdominal obesity (WC ≥90 cm men, ≥80 cm women). Cohen's kappa assessed agreement between definitions and individual components. Logistic regression examined socioeconomic associations with MS using the JIS definition.
**Key Results:** Mean age was 39.9±13.7 years; 53.6% were female. Height, weight, WC, BP, and triglycerides were significantly higher in men; HDL-C was lower (all p<0.05). Overall MS prevalence was 19.4% (NCEP ATP III), 23.6% (IDF), and 25.4% (JIS). By sex, prevalence in men was 15.5%, 21.6%, and 23.8% respectively; in women, 22.8%, 25.3%, and 26.8%. Prevalence increased with age in both sexes. For men, moderate agreement was found between NCEP ATP III and WC (κ=0.42), and between JIS and FBG (κ=0.44) and TG (κ=0.46). For women, moderate agreement was found between NCEP ATP III and HDL-C (κ=0.43), and between JIS and HDL-C (κ=0.43). In multivariable logistic regression using JIS criteria, the 40–59 age group was significantly associated with MS in both men (aOR=1.44, 95% CI 1.01–2.04) and women (aOR=2.28, 95% CI 1.68–3.09). Women aged ≥60 had aOR=3.22 (95% CI 2.04–5.08), and married women had aOR=1.57 (95% CI 1.04–2.36).
**Clinical Implications:** MS is highly prevalent in Mongolia's urban population, affecting approximately one in four adults by JIS criteria. The JIS definition is recommended as the provisional diagnostic standard because it identifies the highest proportion of at-risk individuals and shows moderate agreement with key metabolic components (FBG, TG in men; HDL-C in women). These findings support early screening programs targeting middle-aged and older adults, particularly married women. Given Mongolia's rising burden of diabetes, dyslipidemia, and cardiovascular disease—with only 6.2% awareness of dyslipidemia and inadequate hypertension/diabetes control—adopting the JIS definition could improve early detection. National policies aligned with Mongolia's Sustainable Development Vision 2030 should prioritize MS screening and lifestyle interventions addressing urbanization-related dietary shifts (high fat, low fiber) and physical inactivity.