Monocyte Count, But Not C-Reactive Protein or Interleukin-6, Is an Independent Risk Marker for Subclinical Carotid Atherosclerosis

Background and Purpose - Systemic inflammatory markers have been shown to predict future cardiovascular events, but whether they are associated with early atherosclerosis is uncertain. We investigated the relationship of inflammatory markers interleukin-6 (IL-6), high-sensitive C-reactive protein (hs-CRP), fibrinogen, monocyte count, and white cell count (WCC) with subclinical carotid atherosclerosis in a healthy community population.Methods - B-mode carotid ultrasound was performed on 1111 randomly selected male and female subjects aged 27 to 77 years. Serum IL-6, hs-CRP, plasma fibrinogen, monocyte count, and WCC were measured on all subjects, along with conventional cardiovascular risk factors.Results - Multivariate analysis showed that IL-6 ( P < 0.0001), fibrinogen ( P = 0.007), and monocyte count ( P = 0.001) were associated with carotid plaque formation in the whole population. Monocyte count remained associated independently with carotid plaque formation when adjusted further for conventional risk factors ( odds ratio per SD increase in monocyte count 1.4; 95% CI, 1.13 to 1.73; P = 0.002). IL-6 ( P < 0.0001), fibrinogen ( P < 0.0001), and monocyte count ( P = 0.04) were also associated with carotid intima-medial thickness (IMT) in the whole population. However, when adjusted further for conventional risk factors, none remained independently predictive of carotid IMT. Further analysis showed an age - monocyte interaction ( P = 0.03), with monocyte count being an independent predictor of carotid IMT in the older age group only ( > 53 years; P = 0.003).Conclusion - In a healthy community population, monocyte count is a better independent predictor of common carotid IMT and plaque formation than IL-6, hs-CRP, fibrinogen, and WCC. Monocyte count may represent an inexpensive, easy-to-measure risk marker for subclinical carotid atherosclerosis.