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New data on the intraindividual variation of cystatin C
Pierre Delanaye1, Etienne Cavalier, Gisèle Depas
1Department of Nephrology, University of Liege, CHU Sart Tilman, Liege, Belgium. pierre_delanaye@yahoo.fr
Insights
Cystatin C and creatinine show similar biological variance, making cystatin C a reliable marker for monitoring kidney function over time. This finding supports its use in clinical practice for tracking glomerular filtration rate (GFR).
Area of Science:
- Nephrology
- Clinical Chemistry
Background:
- Cystatin C is an emerging marker for glomerular filtration rate (GFR).
- Limited and conflicting data exist on its biological variance.
- Its reliability for longitudinal renal function monitoring is uncertain.
Purpose of the Study:
- To assess the biological variance of cystatin C compared to creatinine.
- To determine the suitability of cystatin C for long-term renal function tracking.
Main Methods:
- 12 healthy subjects (6 males, 6 females) participated.
- Serum creatinine, plasma cystatin C, and GFR were measured twice over a 1-week interval.
- GFR was determined using an iohexol method; creatinine with Jaffé and enzymatic methods; cystatin C with immunonephelometry.
Main Results:
- Analytical variance (CV(A)) for cystatin C was 1.29%, similar to enzymatic creatinine (0.97%) and Jaffé creatinine (2.5%).
- Within-subject variance (CV(I)) for cystatin C was 4.5%, comparable to enzymatic creatinine (5%) and Jaffé creatinine (5.8%).
Conclusions:
- Intraindividual variation of cystatin C and creatinine are comparable.
- Cystatin C is biologically as accurate as creatinine for longitudinal renal function monitoring in clinical practice.
Background:
Cystatin C is a new interesting marker of glomerular filtration rate (GFR). However, data regarding its biological variance are scarce and conflicting. The ability of cystatin C to longitudinally follow renal function in patients therefore remains questionable.
Methods:
12 healthy subjects (6 men and 6 women) were included in the final statistical analysis. Serum creatinine, plasma cystatin C and GFR were measured twice after a 1-week interval on the same day, at the same time, and under the same preanalytical and analytical conditions. GFR was measured with an iohexol method. Serum creatinine was measured with a compensated Jaffé and an enzymatic method. Plasma cystatin C was measured by a particle-enhanced immunonephelometric method. Analytical (CV(A)) and within-subject (CV(I)) variances were classically calculated.
Results:
CV(A) for creatinine (Jaffé and enzymatic methods) and cystatin C was 2.5, 0.97 and 1.29%, respectively. CV(I) was 5.8, 5 and 4.5% for the Jaffé creatinine, enzymatic creatinine and cystatin C determinations, respectively.
Conclusion:
Our study confirms that intraindividual variation of cystatin C and creatinine are similar. Therefore, from a biological point of view, cystatin C seems as accurate as creatinine for the longitudinal follow-up of renal function in daily clinical practice.
