**Background:** Metabolic syndrome (MetS) is a growing global health concern linked to chronic inflammation. Haematological inflammatory parameters from routine complete blood counts (CBC) may serve as accessible, cost-effective predictors of MetS. This study aimed to determine the relationship between haematological parameters and MetS in the adult population of southeastern Iran, Kerman.
**Methods:** This cross-sectional study was a sub-analysis of 1,033 subjects (660 women, 373 men) from the second phase of the Kerman Coronary Artery Disease Risk Factor Study (KERCADRS), conducted from February 2017 to October 2018. Participants with a history of chronic infectious or inflammatory diseases or use of drugs affecting haematological parameters or lipoprotein metabolism were excluded. MetS was diagnosed using the Adult Treatment Panel III (ATP III) definition (≥3 of: blood pressure >130/80 mmHg or antihypertensive use; triglycerides >150 mg/dL; fasting plasma glucose >100 mg/dL or anti-diabetic medication; HDL <40 mg/dL in men or <50 mg/dL in women; waist circumference >102 cm in men or >88 cm in women). Demographic data, anthropometric measurements, blood pressure, and fasting blood samples were collected. Pearson and Spearman correlation coefficients were used to assess relationships between haematological parameters and MetS components. Receiver operating characteristic (ROC) curves with Youden index were used to determine optimal cut-off values for WBC, neutrophil, lymphocyte, and monocyte in predicting MetS.
**Key Results:** Among 1,033 participants, 82 men and 197 women had MetS. In both sexes, participants with MetS had significantly higher age, BMI, waist circumference, waist-to-hip ratio, systolic and diastolic blood pressure, fasting plasma glucose, triglycerides, MHR, and NHR (all p<0.001). In females with MetS, WBC (6.92±1.52 vs. 6.30±1.66 ×10³/μL, p<0.001), neutrophil (3.70±1.12 vs. 3.35±1.21, p=0.001), lymphocyte (2.46±0.68 vs. 2.24±0.66, p<0.001), monocyte (0.54±0.15 vs. 0.51±0.14, p=0.005), and RDW-SD (43.56±3.10 vs. 42.94±2.98, p=0.017) were significantly higher than in females without MetS. WBC count, neutrophil, lymphocyte, monocyte, RDW-SD, RDW-CV, MHR, and NHR showed significant positive correlations with the number of MetS components (severity), while PLR showed a significant negative correlation. WBC was significantly correlated with all metabolic components except age. For predicting MetS, WBC had better accuracy in females (AUC=0.632; p<0.001; 95% CI: 0.594–0.669) than in males (AUC=0.564; p=0.074; 95% CI: 0.512–0.615). The optimal cut-off for WBC was 6.15 ×10³/μL in females (sensitivity 70.05%, specificity 52.92%, Youden index 0.230) and 6.34 ×10³/μL in males (sensitivity 68.29%, specificity 46.74%, Youden index 0.150). Neutrophil, lymphocyte, and monocyte showed lower predictive accuracy. NLR was not a significant predictor of MetS in this study.
**Clinical Implications:** This study provides evidence from southeastern Iran that routine haematological parameters—particularly WBC, its subcomponents, RDW, MHR, and NHR—are significantly associated with MetS and its severity. These markers are readily available from standard CBC tests and could serve as low-cost screening tools for early identification of individuals at risk for MetS. The sex-specific cut-off values for WBC (6.1 ×10³/μL for females, 6.3 ×10³/μL for males) may help clinicians flag patients requiring further metabolic assessment. However, as a cross-sectional study, causality cannot be established, and the relatively small sample size with female predominance limits generalizability. Prospective studies are needed to confirm these findings and to evaluate whether haematological parameters should be incorporated into MetS diagnostic criteria.