Fetuin-A and kidney function in persons with coronary artery disease--data from the Heart and Soul Study.

BACKGROUND Fetuin-A is a serum protein that inhibits ectopic vascular calcification and is present in lower concentrations in end-stage renal disease than in healthy controls. Whether fetuin-A concentrations are also lower in the setting of mild-to-moderate chronic kidney disease (CKD) is unknown. METHODS We evaluated the associations of several parameters of kidney function including measured 24 h urinary creatinine clearance (CrCl), estimated glomerular filtration rate (GFR) by the Mayo Clinic quadratic GFR equation (qGFR), serum cystatin-C concentrations, and urinary albumin-to-creatinine ratio with serum fetuin-A concentrations in 970 outpatients with coronary artery disease. We used general linear models to determine the adjusted mean fetuin-A concentrations within each kidney function category. RESULTS The mean age of the study sample was 67 years, 82% were male, 71% had hypertension and 26% had diabetes mellitus. In adjusted analysis, we observed no significant differences in mean fetuin-A concentrations across groups defined by CrCl, qGFR, or albumin-to-creatinine ratio groups. For example, adjusted mean fetuin-A concentrations were 0.66 g/l in participants with CrCl > 90, 60-90 and 45-60 ml/min/1.73 m(2), and 0.65 g/l in participants with CrCl < 45 ml/min/1.73 m(2). Higher serum cystatin-C (indicating worse kidney function) was associated with higher adjusted mean serum fetuin-A concentrations (lowest quartile 0.62 g/l, highest quartile 0.68 g/l; P for trend <0.001). CONCLUSIONS Among ambulatory patients with coronary artery disease, there is no evidence that mild-to-moderate CKD is associated with lower concentrations of serum fetuin-A compared with persons with normal renal function. The mechanisms explaining the association between CKD and vascular calcification remain elusive.