title: Serum levels of cystatin C in patients with malignancy.
abstract: BACKGROUND
  Serum levels of cystatin C have been proposed to be an ideal marker of the glomerular filtration rate (GFR). However, some reports have shown that serum levels of cystatin C increase independently of GFR. In this study, we evaluated the clinical utility of cystatin C in monitoring GFR, especially in patients with a malignancy.
  
  
  METHODS
  Study subjects consisted of 82 patients with a malignancy, 39 patients with a non-malignancy, 31 healthy volunteers, and 206 patients with various degrees of renal function. We measured serum cystatin C, beta2-microglobulin (beta 2mG), and creatinine (CRE) levels in all patients. Serum CRP levels were measured in 21 patients with a malignancy and 28 patients with a non-malignancy whose creatinine clearance (Ccr) was > or =70 ml/min. Cystatin C, beta 2mG, and CRP were measured by immune nephelometry and CRE was measured by an enzyme assay.
  
  
  RESULTS
  In patients with a malignancy, regression analysis yielded the equation: 1/cystatin C = 0.06 x Ccr + 0.710, correlation coefficient, r, of 0.33. The r was significantly lower than in patients with various degrees of renal function. There were no significant differences when the r performed on beta 2mG and CRE was compared between the same groups of patients. In 74 patients with a malignancy, in whom serum CRE levels were < or =1.1 mg/dl, increased levels of cystatin C were observed in 25 patients and increased levels of beta 2mG were observed in 39 patients. In comparing patients with a malignancy and a non-malignancy, the number of patients with an increased level of cystatin C, despite a Ccr > or = 70 ml/min (8/33) or a CRE < or = 1.1 mg/dl (13/41), was larger in the former group than the latter group, although the result was not statistically significant. Similarly, the number of patients with an increased level of beta 2mG, despite a Ccr > or = 70 ml/min or a CRE < or = 1.1 mg/dl was significantly larger in the former group compared to the latter group. Regression analysis between the serum levels of cystatin C and CRP in patients with a malignancy whose Ccr were > or =70 ml/min had a weak correlation (r = 0.31).
  
  
  CONCLUSIONS
  The results of our study suggest that the serum levels of cystatin C are not always a reliable marker of the GFR in patients with a malignancy, probably in relation to its nature as a cysteine protease inhibitor.
authors.affiliation: Department of Laboratory Medicine, Iwate Medical University, 19-1 Uchimaru, Morioka, 020-8505, Japan. keikoyn@iwate-med.ac.jp.
authors.forename: Keiko
authors.initials: K
authors.lastname: Nakai
authors.affiliation: Department of Clinical Laboratory, Iwate Medical University Hospital, Morioka, Japan.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Kikuchi
authors.affiliation: Department of Clinical Laboratory, Iwate Medical University Hospital, Morioka, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Fujimoto
authors.affiliation: Department of Diabetes and Metabolism, Iwate Medical University, Morioka, Japan.
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Kaneko
authors.affiliation: Department of Urology, Iwate Medical University, Morioka, Japan.
authors.forename: So
authors.initials: S
authors.lastname: Omori
authors.affiliation: Department of Laboratory Medicine, Iwate Medical University, 19-1 Uchimaru, Morioka, 020-8505, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Nakai
authors.affiliation: Department of Laboratory Medicine, Iwate Medical University, 19-1 Uchimaru, Morioka, 020-8505, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Suwabe
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000097:blood; D003404:Creatinine / Q000097:blood; D055316:Cystatin C; D015891:Cystatins / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000378:metabolism* / Q000503:physiopathology; D011237:Predictive Value of Tests; D012016:Reference Values; D012044:Regression Analysis; D015203:Reproducibility of Results; D001613:beta 2-Microglobulin / Q000097:blood
chemical_list: D015415:Biomarkers; C525030:CST3 protein, human; D055316:Cystatin C; D015891:Cystatins; D001613:beta 2-Microglobulin; D003404:Creatinine