Blood viscosity as a continuous marker of cardio-metabolic risk burden: a large-scale cross-sectional study of 38,574 adults.

AIMS: Metabolic syndrome (MetS) is diagnosed using fixed thresholds that may not fully reflect the continuous accumulation of cardio-metabolic risk. We investigated whether whole blood viscosity (WBV) increases progressively with increasing MetS burden and explored the relative contribution of individual MetS components to hemorheologic alterations. METHODS: We analyzed 38,574 adults (21,914 men and 16,660 women) who underwent comprehensive health examinations between January and April 2021. Whole blood viscosity was measured by cone-plate viscometry at shear rates of 300 s-1 (systolic blood viscosity [SBV]) and 5 s-1 (diastolic blood viscosity [DBV]). MetS was defined according to NCEP-ATP III criteria. Associations between WBV and MetS burden were evaluated using logistic regression, ANCOVA, regression tree analyses, ROC analyses, and sex-by-viscosity interaction testing. RESULTS: WBV increased progressively with each additional MetS component in both sexes (p for trend <0.001). After full adjustment for hematocrit, age, smoking status, eGFR, white blood cell count, and AST/ALT, higher SBV was associated with MetS in both women (OR 1.45, 95% CI 1.32-1.58, per 1-SD increase) and men (OR 1.27, 95% CI 1.22-1.33, per 1-SD increase). Regression tree analyses identified triglycerides and waist circumference as metabolic factors associated with elevated WBV. Sex-stratified analyses demonstrated a stronger association between WBV and MetS in women than in men. CONCLUSIONS: WBV increased in parallel with accumulating cardio-metabolic risk burden, including among individuals who did not meet diagnostic criteria for MetS. WBV may serve as a complementary marker associated with metabolic risk burden, particularly among women and individuals with hypertriglyceridemia or central adiposity.