Association of cystatin C and estimated GFR with inflammatory biomarkers: the Heart and Soul Study

Background. Cystatin C is a marker of kidney function that may also be associated with inflammation. In this study, we compared the relative strengths of association of cystatin C and estimated glomerular filtration rate (eGFR) with inflammatory biomarkers. Methods. We measured serum cystatin C and creatinine in 990 outpatients with coronary artery disease enrolled in the Heart and Soul Study. GFR was estimated (eGFR) by the abbreviated Modification of Diet in Renal Disease (MDRD) equation. We compared the associations of serum cystatin C and eGFR with C-reactive protein (CRP) and fibrinogen, after adjustment for 24 h creatinine clearance. Results. Cystatin C concentrations had moderate correlations with CRP (r = 0.15, P < 0.001) and fibrinogen (r = 0.26, P < 0.0001); eGFR had similar correlations with CRP (r = -0.17, P = 0.01) and fibrinogen (r = -0.25, P < 0.001) among persons with eGFR <= 60 ml/min, but had no association with either biomarker among those with eGFR > 60 ml/min (r = 0.04, P = 0.32; r = -0.03, P = 0.38). Quartiles of cystatin C were strongly and directly associated with CRP (P = 0.02) and fibrinogen (P < 0.007) after multivariate adjustment. However, these associations disappeared after adjustment for creatinine clearance (P = 0.26 and 0.23, respectively). Conclusions. Cystatin C concentrations have moderate associations with CRP and fibrinogen that are not independent of creatinine clearance. Although a gold standard of kidney function is lacking, this analysis suggests that cystatin C captures an association of mildly impaired kidney function with increased inflammation.