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GFR Estimation Using Cystatin C Is Not Independent of Body Composition

2006; Elsevier BV; Volume: 48; Issue: 5 Linguagem: Inglês

10.1053/j.ajkd.2006.07.001

1523-6838

Jamie Macdonald, Samuele Marcora, Mahdi Jibani, Gareth W. Roberts, Mick Kumwenda, Ruth Glover, Jeffrey Barron, Andrew Lemmey,

Dialysis and Renal Disease Management

Background: Cystatin C (CysC) is an endogenous marker of glomerular filtration rate (GFR) that is claimed to be unaffected by body composition. In this study, we tested this speculation. Methods: In 77 patients with chronic kidney disease (mean age, 65.1 ± 11.9 [SD] years; mean indexed GFR, 45.7 ± 28.6 mL/min/1.73 m2 [0.76 ± 0.48 mL/s]), we evaluated kidney function (GFR) by means of inulin clearance. CysC level was determined by using a particle-enhanced turbidimetric immunoassay. Total lean (LM) and fat masses were measured by means of dual-energy x-ray absorptiometry. Multiple regression was used to analyze relationships between absolute GFR, LM, fat mass, demographic and anthropometric variables (age, sex, height, and weight), and CysC levels. Then prediction equations were built that included only CysC level or CysC level and LM. Their performance to predict absolute GFR was evaluated in a subset of patients with extreme body composition (LM or fat mass > ±1 SD of the entire sample). Results: Only absolute GFR and LM significantly explained variance in CysC levels, and an equation including LM explained more variance in absolute GFR than an equation including CysC level alone. Consequently, the equation including LM performed better than the equation with only CysC level, especially in patients with extreme body composition, showing reduced bias and improved limits of agreement and accuracy (71.4% versus 51.4% of patients’ predicted GFR did not deviate by >30% of GFR). Conclusion: LM is a previously unrecognized, but important, factor affecting CysC level, and GFR estimation improves when including LM. CysC level is not independent of body composition, as previously assumed, and hence accounting for body composition improves CysC-based GFR estimation. Background: Cystatin C (CysC) is an endogenous marker of glomerular filtration rate (GFR) that is claimed to be unaffected by body composition. In this study, we tested this speculation. Methods: In 77 patients with chronic kidney disease (mean age, 65.1 ± 11.9 [SD] years; mean indexed GFR, 45.7 ± 28.6 mL/min/1.73 m2 [0.76 ± 0.48 mL/s]), we evaluated kidney function (GFR) by means of inulin clearance. CysC level was determined by using a particle-enhanced turbidimetric immunoassay. Total lean (LM) and fat masses were measured by means of dual-energy x-ray absorptiometry. Multiple regression was used to analyze relationships between absolute GFR, LM, fat mass, demographic and anthropometric variables (age, sex, height, and weight), and CysC levels. Then prediction equations were built that included only CysC level or CysC level and LM. Their performance to predict absolute GFR was evaluated in a subset of patients with extreme body composition (LM or fat mass > ±1 SD of the entire sample). Results: Only absolute GFR and LM significantly explained variance in CysC levels, and an equation including LM explained more variance in absolute GFR than an equation including CysC level alone. Consequently, the equation including LM performed better than the equation with only CysC level, especially in patients with extreme body composition, showing reduced bias and improved limits of agreement and accuracy (71.4% versus 51.4% of patients’ predicted GFR did not deviate by >30% of GFR). Conclusion: LM is a previously unrecognized, but important, factor affecting CysC level, and GFR estimation improves when including LM. CysC level is not independent of body composition, as previously assumed, and hence accounting for body composition improves CysC-based GFR estimation. Estimating GFR From Cystatin C in Serum: Seeking to Enhance Its Clinical ApplicationAmerican Journal of Kidney DiseasesVol. 48Issue 5PreviewALTHOUGH GLOMERULAR FILTRATION rate (GFR) yields the best estimates of kidney function in people, measurements of GFR are much too complicated to be used routinely in the clinical setting. Nationally a concerted effort has been initiated to raise the awareness of detecting kidney disease, at its earliest stages ( http://www.nkdep.nih.gov ). Over decades many equations have been devised to calculate an estimated GFR (eGFR) from serum creatinine concentrations.1,2 Currently most of these efforts center on eGFR from the Modification of Diet in Renal Disease equations. Full-Text PDF Accounting for Body Composition does not Improve Cystatin C Estimation of GFR in Diabetic Subjects with CKDAmerican Journal of Kidney DiseasesVol. 49Issue 4PreviewMacdonald et al1 recently reported that cystatin C (CysC) levels were influenced by lean body mass (LM) in patients with chronic kidney disease and developed glomerular filtration rate (GFR)-predictive equations based on CysC level alone (GFRCysC) or associated with LM (GFRLM) or demographic variables (GFRdemo). We compared them with isotopic GFRs in 41 patients with diabetes (31 men; 31 patients with type 2 diabetes; age, 65 ± 12 years; body mass index, 26.0 ± 4.6 kg/m2). We measured LM (dual-energy X-ray absorptiometry) and CysC (immunonephelometry; N-Latex Cystatin C; Dade Behring, Marburg, Germany). Full-Text PDF