European Heart Journal Advance Access originally published online on October 16, 2007
European Heart Journal 2007 28(22):2818; doi:10.1093/eurheartj/ehm432
Cystatin C blood level as a risk factor for death after heart surgery
Medical Intensive Care Unit
Department of medicine
University Hospital of Liege
CHU Sart Tilman B35
4000 Liege
Belgium
Emergency Care Department University Hospital of Liege Belgium
Tel: +32 4 366 71 11 fax: +32 4 366 77 23 E-mail address: b.lambermont{at}chu.ulg.ac.be
We read with interest the manuscript of Ledoux et al.1 entitled ‘Cystatin C blood level as a risk factor for death after heart surgery’ in the last issue of European Heart Journal. In this study they showed that glomerular filtration rate (GFR) estimated from cystatin C but not from creatinine was an independent risk fact or for hospital morbidity/mortality and for 1-year mortality.
One accepted limitation of cystatin C as a marker of GFR is that it requires a conversion formula which transforms cystatin C (expressed as mg/L) to GFR (expressed as mL/min).2 Since several commercial systems for measuring serum and plasma cystatin C are available, this could cause problems.3,4 Effectively, different cystatin C-based prediction equations for GFR have to be used according to assay methods used to achieve maximal diagnostic performance.5–7
In this study, Ledoux et al.1 used the particle-enhanced nephelometric immunoassay (PENIA) method (Dade Behring, Marburg, Germany) and the following formula to transform cystatin C plasma levels, expressed as mg/L, to GFR expressed as mL/min:
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\hbox{GFR}=84.69 \times \hbox{Plasma cystatin C}^{-1.68} \times 0.948\ (\hbox {if female}) \eqno(1)
| (1) |
Unfortunately, this formula must be used when the particle-enhanced turbidimetric immunoassay (PETIA) method is used.5 When the PENIA method is used to measure cystatin C plasma level, as was the case in this study, it is more accurate to apply the following formula to convert cystatin C plasma levels to GFR values:2,7
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\hbox{GFR}=66.8 \times \hbox{Plasma cystatin C}^{-1.3} \eqno(2)
| (2) |
These two conversion formulae are not interchangeable and can lead to significant differences in calculated GFR ranging from + 40 to – 25% as shown in Table 1.
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It would be of great interest to know whether the results and the conclusion of this study would be similar when using the alternate formula to calculate GFR from cystatin plasma level.
References
- Ledoux D, Monchi M, Chapelle JP, Damas P. Cystatin C blood level as a risk factor for death after heart surgery. Eur Heart J (2007) 28:1848–1853.
[Abstract/Free Full Text] - Herget-Rosenthal S, Bokenkamp A, Hofmann W. How to estimate GFR – serum creatinine, serum cystatin C or equations? Clin Biochem (2007) 40:153–161.[CrossRef][Web of Science][Medline]
- Finney H, Newman DJ, Gruber W, Merle P, Price CP. Initial evaluation of cystatin C measurement by particle-enhanced immuno nephelometry on the behring nephelometer systems (BNA, BN II). Clin Chem (1997) 43:1016–1022.
[Abstract/Free Full Text] - Newman DJ. Cystatin C. Ann Clin Biochem (2002) 39:89–104.[CrossRef][Web of Science][Medline]
- Grubb A, Nyman U, Bjork J, Lindstrom V, Rippe B, Sterner G, Christensson A. Simple cystatin C-based prediction equations for glomerular filtration rate compared with the modification of diet in renal disease prediction equation for adults and the Schwartz and the Counahan–Barratt prediction equations for children. Clin Chem (2005) 51:1420–1431.
[Abstract/Free Full Text] - Larsson A, Malm J, Grubb A, Hansson LO. Calculation of glomerular filtration rate expressed in mL/min from plasma cystatin C values in mg/L. Scand J Clin Lab Invest (2004) 64:25–30.[CrossRef][Web of Science][Medline]
- Rule AD, Bergstralh EJ, Slezak JM, Bergert J, Larson TS. Glomerular filtration rate estimated by cystatin C among different clinical presentations. Kidney Int (2006) 69:399–405.[CrossRef][Web of Science][Medline]
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