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      Cystatin C as an Endogenous Marker of Glomerular Filtration Rate in Renal Transplant Patients

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          Background: Serum creatinine is the most common endogenous marker used to estimate the glomerular filtration rate (GFR). However, creatinine depends considerably on muscle mass, and its tubular secretion increases, especially in chronic renal failure. Cystatin C is a 13-kD protease inhibitor which is produced by all nucleated cells and is independent of muscle mass and sex. Cystatin C is eliminated by glomerular filtration and metabolized by proximal tubular cells. Its measurement has been proposed as an alternative and more sensitive marker of GFR than creatinine in patients with slight to moderately decreased GFR. Methods: We investigated serum cystatin C levels in comparison with creatinine as a single measurement for estimation of GFR in 173 patients after renal transplantation. GFR was calculated as creatinine clearance according to standard equations. Results: Serum creatinine correlated well with cystatin C (r = 0.84; p < 0.0001). No significant differences were obtained for the comparison of the linear correlation of 1/creatinine with creatinine clearance (r = 0.77; p < 0.0001) and for the linear correlation of 1/cystatin C with creatinine clearance (r = 0.73; p < 0.0001). However, we found a significant advantage of cystatin C in detecting a clinical relevant reduction of kidney function (GFR <70 ml/min; p = 0.0047, McNemar test). Conclusion: Cystatin C is an alternative marker for the assessment of GFR in renal allograft recipients that may be superior to creatinine.

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          Serum cystatin C as a marker of the renal function.

          The protease inhibitor cystatin C is a non-glycosylated low molecular weight protein (Mr=13359) which is produced by all nucleated cells at a constant rate, freely filtered by the renal glomeruli, and catabolized in the tubuli. The aim of the study was to elucidate the applicability of serum cystatin C as a marker of glomerular filtration rate (GFR) in patients with various kidney diseases with a wide range of renal function and in dialysis patients. Seventy-six patients with various kidney diseases (aged 20 to 79 years) and 61 dialysis patients (aged 21 to 82 years) were included. Serum cystatin C was measured by automated particle-enhanced immunoturbidimetry, serum and urine creatinine by an enzymatic method, and GFR by 99mTc-DTPA-clearance using a single plasma sample method. Serum cystatin C in patients with various kidney diseases was 1.90+/-0.98 mg/L (mean+/-SD) and in dialysis patients 7.14+/-1.91 mg/L. In the non-dialysis patients a linear relationship was found between 99mTc-DTPA-clearance and 1/serum cystatin C (r=0.91, p-value<0.0001), 1/serum creatinine (r=0.89, p-value<0.0001), and creatinine-clearance (r=0.88, p-value<0.0001). Comparison of the non-parametric ROC plots for serum cystatin C (area under the curve (AUC)=0.9665; SE=0.0169), serum creatinine (AUC=0.9554; SE=0.0205), and creatinine-clearance (AUC=0.9731; SE=0.0160) revealed no significant differences (p-values: 0.50, 0.78, and 0.49). In conclusion, cystatin C may be a likewise good marker of the GFR as serum creatinine and creatinine-clearance, cystatin C having the advantage being independent of gender and muscle mass.
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            Serum cystatin C is a better marker for preeclampsia than serum creatinine or serum urate.

            Altered renal function is an essential component of the pathophysiological process in preeclampsia. The kidneys play a significant part in the turnover of most low molecular weight substances such as creatinine, urate and cystatin C. The present work was undertaken to investigate if the serum levels of these components are altered in characteristic ways in preeclampsia, and can be used to assist in the diagnosis of this condition. The serum levels were therefore determined in samples from 100 healthy women at term as well as in 45 samples of patients with preeclampsia (diastolic blood pressure >90 mmHg; urinary albumin excretion >300 mgL(-1)). The levels of all three components were significantly higher in samples from preeclamptic patients with the mean+SD being 1.55+/-0.29 vs. 1.05+/-0.19 mg L(-1) for cystatin C, 70+/-23 vs. 56+/-9.7 micromol L(-1) for creatinine, and 413+/-128 vs. 305+/-61 micromol L(-1) for urate. Receiver operating characteristic analysis demonstrated that the serum level of cystatin C had a superior diagnostic accuracy for preeclampsia compared to those of serum urate and creatinine and that the diagnostic accuracy of serum urate was better than that of serum creatinine.
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              Measurement of Glomerular FiltrationRate by the 99m < /sup>Tc-DTPA Renogram Is Less Precise than Measured and Predicted Creatinine Clearance

              The work was devised to compare measurements of glomerular filtration rate (GFR) by technetium-99m-diethylenetriaminepentacetic acid ( 99m Tc-DTPA) renogram to those by creatinine clearance (measured and predicted by Cockroft and Gault) and by inulin clearance. A total number of 65 individuals were enrolled: 15 healthy controls and 50 patients with renal disease. Compared to inulin clearance used as the gold standard, 99m Tc-DTPA overestimated at low and underestimated at high GFRs. 99m Tc-DTPA measurements were less precise than creatinine clearance except for individuals with GFR >100 ml/min × 1.73 m 2 . Measured creatinine clearance had the highest correlation coefficient with inulin clearance, 99m Tc-DTPA clearance the lowest. In correlation analyses, 81.5% of the interindividual variability for measured creatinine clearance could be explained by true differences in inulin clearance; this value dropped to 59.1 and 57.4% for predicted creatinine clearance and 99m Tc-DTPA, respectively. In patients with GFR 2 , all 99m Tc-DTPA measurements were out of the 95% confidence interval for the inulin measurement. It can be inferred that 99m Tc-DTPA clearance from the renogram is less precise than measured and predicted creatinine clearance.

                Author and article information

                Kidney Blood Press Res
                Kidney and Blood Pressure Research
                S. Karger AG
                24 April 2003
                : 26
                : 1
                : 55-60
                Departments of aInternal Medicine I and bClinical Biochemistry, University of Bonn, Germany
                69767 Kidney Blood Press Res 2003;26:55–60
                © 2003 S. Karger AG, Basel

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                Figures: 1, Tables: 3, References: 30, Pages: 6
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