Serum C3 is a stronger inflammatory marker of insulin resistance than C-reactive protein, leukocyte count, and erythrocyte sedimentation rate: comparison study in an elderly population.

OBJECTIVE This study was performed to ascertain the relative relevance of some inflammatory markers in insulin resistance. RESEARCH DESIGN AND METHODS Four inflammatory markers (leukocyte count, erythrocyte sedimentation rate [ESR], high-sensitivity C-reactive protein [CRP], and C3 complement) were assessed as possible determinants of the homeostasis model assessment (HOMA) index, together with the five elements of the metabolic syndrome (National Cholesterol Education Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults [Adult Treatment Panel III] definition), total cholesterol, physical activity, and four indicators of adiposity (BMI, waist circumference, percent body fat, and hepatic steatosis) in an unselected population of 990 subjects aged 65-91 years (the Pianoro Study). RESULTS In univariable analysis, C3, CRP, and leukocyte count, but not ESR, were significantly correlated with HOMA index. In multivariable analysis, C3 remained associated with insulin resistance with the highest partial R(2) value (0.049), independently of all other covariates. The other most significant (P < 0.0001) determinants of HOMA index were total cholesterol (inverse association, R(2) = 0.026), waist circumference (R(2) = 0.023), triglycerides (R(2) = 0.022), and hepatic steatosis (R(2) = 0.021) (R(2) = 0.450 for the whole model). The adjusted relative risks of having the metabolic syndrome for the subjects with inflammatory markers in the high tertile, with respect to those with lower values, were (prevalence ratio [95% CI]): 1.77 (1.41-2.22) for C3, 1.38 (1.12-1.70) for leukocyte count, 1.17 (0.94-1.46) for CRP, and 1.13 (0.91-1.40) for ESR. CONCLUSIONS Of the four inflammatory markers simultaneously assessed in our elderly population, only C3 was strongly associated with insulin resistance, independently of the components of the metabolic syndrome and the main indexes of abdominal and general obesity.