Circulating matrix metalloproteinase 9 levels in relation to sampling methods, femoral and carotid atherosclerosis

. Objectives. To examine whether circulating levels of matrix metalloproteinase 9 (MMP‐9) were associated with ultrasound‐assessed intima‐media thickness (IMT) and echolucent plaques in the carotid and femoral arteries. To examine preanalytical sources of variability in MMP‐9 concentrations related to sampling procedures. Subjects and design. Plasma and serum MMP‐9 levels were compared with ultrasound assessed measures of femoral and carotid atherosclerosis, in a cross‐sectional study of 61‐year‐old men (n = 473). Preanalytical sources of variability in MMP‐9 levels were examined in 10 healthy subjects. Main outcome measures were circulating levels of MMP‐9 in serum and plasma, IMT of the carotid and femoral arteries, and plaque status based on size and echolucency. Setting. Research unit at university hospital. Results. Plasma concentrations of total and active MMP‐9 were associated with femoral artery IMT independently of traditional cardiovascular risk factors, and were higher in subjects with moderate to large femoral plaques. Plasma MMP‐9 concentration was higher in men with echolucent femoral plaques (P = 0.006) compared with subjects without femoral plaques. No similar associations were found for carotid plaques. MMP‐9 concentrations were higher in serum than in plasma, and higher when sampling was performed with Vacutainer than with syringe. MMP‐9 levels in serum were more strongly associated with peripheral neutrophil count compared with MMP‐9 levels in plasma. Conclusions. Plasma MMP‐9 levels were associated with atherosclerosis in the femoral artery, and total MMP‐9 concentration was higher in men with echolucent femoral plaques. The choice of sample material and sampling method affect the measurements of circulating MMP‐9 levels.