Reference Intervals for Plasma Cystatin C in Healthy Volunteers and Renal Patients, as Measured by the Dade Behring BN II System, and Correlation with Creatinine

Abstract

Cystatin C (cysC) is a 132-amino acid, 13-kDa cysteine protease inhibitor produced by all nucleated cells and whose function is thought to be modulation of the intracellular catabolism of proteins (1). It is formed at a constant rate, freely filtered by the renal glomeruli, and completely reabsorbed and catabolized by the proximal tubular cells (1)(2)(3)(4)(5). Plasma cysC values are reported to be unaffected by age, body weight, diet, medications, or pathologies such as inflammation and cancer. On the basis of these favorable characteristics, cysC has been proposed as a marker of glomerular filtration rate (3)(4)(5)(6). Serum creatinine (creatinine) is widely used for estimation of the glomerular filtration rate, but its tubular secretion, dependence on muscle mass, alteration in some inflammatory diseases, and analytical interferences can limit its utility (7)(8)(9)(10). Thus, cysC has been proposed as an alternative marker in some settings (3)(4)(9)(11)(12). The purpose of this study was to evaluate the analytical and clinical performance characteristics of a new cysC assay and to establish adult reference intervals for cysC. One hundred thirty-nine presumably healthy adult volunteers participated in the study (age >18 years; 78 females and 61 males) by donating a plasma specimen for creatinine and cysC measurements. Volunteers were recruited with posted signs around our medical center and were offered $25.00 compensation. All volunteers filled …