Measurement of cystatin-C and creatinine in urine.
BACKGROUND
The concentration of serum cystatin-C (Cys-C) is highly correlated with creatinine (Cr), and is mainly determined by glomerular filtration; thus, Cys-C may be an index of the glomerular filtration rate (GFR). However, the kinetics of urinary Cys-C and Cr excretions are unclear. Thus, we investigated the kinetics of urinary Cys-C and Cr excretions, and examined whether the urinary Cys-C concentration can be used as a marker of renal function.


METHODS
The urinary excretion of Cys-C and Cr was evaluated in 1670 healthy subjects and 217 patients with proteinuria. We also investigated the urinary Cys-C concentration in 52 patients with chronic renal failure.


RESULTS
There was a good correlation between the urinary concentrations of Cys-C and Cr in the healthy group. This relation was also observed in patients showing persistent proteinuria without tubular cell damage. The mean urinary Cr concentration increased with age, and it was affected by the muscle mass. In contrast, the urinary Cys-C concentration was not affected by the muscle mass, and the concentration remained constant for all ages. We further found that the ratio of Cys-C to Cr (CCR) is a good index of the state of Cys-C reabsorption in the proximal tubules.


CONCLUSIONS
The urinary CCR can be a marker of renal tubular dysfunction. In addition, when CCR was in the normal range, the urinary Cys-C concentration accurately reflected the glomerular filtration function.
Uchida
Kazuo
K
Kyoto Medical Science Laboratory, 328 Furukawa-cho, Hazukashi Fushimi-ku, 612-8486, Kyoto, Japan. uchidakz@mb.infoweb.ne.jp
Gotoh
Akiko
A
D000293:Adolescent; D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology; D015415:Biomarkers / Q000652:urine; D016022:Case-Control Studies; D002648:Child; D002908:Chronic Disease; D003404:Creatinine / Q000652:urine*; D055316:Cystatin C; D015891:Cystatins / Q000737:chemistry / Q000652:urine*; D006801:Humans; D007677:Kidney Function Tests; D007700:Kinetics; D016015:Logistic Models; D008875:Middle Aged; D009393:Nephritis / Q000652:urine; D011507:Proteinuria / Q000201:enzymology / Q000652:urine*; D011776:Pyuria / Q000382:microbiology / Q000652:urine; D012015:Reference Standards; D051437:Renal Insufficiency / Q000652:urine*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D001613:beta 2-Microglobulin / Q000652:urine
D015415:Biomarkers; C525030:CST3 protein, human; D055316:Cystatin C; D015891:Cystatins; D001613:beta 2-Microglobulin; D003404:Creatinine