Given the task definition and input, reply with output. In this task, you are given a passage which has a question and the context. You have to generate an answer to the question based on the information present in the context.

Context: Serum cystatin C has been established as a predictor of cardiovascular events. The aim of this study was to evaluate the role of cystatin C in determining the presence and the severity of patients with coronary artery disease (CAD).', 'A total of 936 subjects without overt renal disease were included in this cross-sectional study. Among them were 714 patients with CAD and 222 without based on coronary angiography. Subjects were further divided into four groups according to cystatin C quartile. Serum cystatin C was measured using particle-enhanced immunoassay method. The study analyzed the relationship of cystatin C levels with the presence and severity of CAD, including the number of stenotic vessels involved and Gensini score.', 'Serum cystatin C levels were significantly higher in patients with CAD than those without (P<0.001), and significantly increased as the involvement of coronary vessels increased (P<0.001). The prevalence of CAD and its severity assessed by Gensini score were also significantly greater in the highest quartile of cystatin C (P<0.001). Moreover, cystatin C levels were independently correlated with the presence of CAD in a multivariate logistic regression model (P=0.023) and were positively correlated with Gensini score by linear regression analysis (standardized =0.083, P=0.010).\Question: Are serum cystatin C levels associated with coronary artery disease and its severity?
Elevated serum cystatin C levels were significantly associated with the presence and severity of CAD in patients with normal renal function. It is suggested that cystatin C might play a role in CAD diagnosis and serve as a marker of CAD severity.