The Search for a New Marker of Renal Function in Older Patients with Chronic Kidney Disease Stages 3–4: Usefulness of Cystatin C-Based Equations

Abstract

Background/Aim: Cystatin C (Cys C) is an endogenous marker of glomerular filtration rate (GFR) unaffected by body composition. The aim of the present study was to assess the utility of Cys C-based GFR prediction equations (Hoek, Larsson and Stevens) and creatinine (modification of diet in renal disease-isotope dilution mass spectrometry – MDRD-IDMS, and Cockcroft-Gault – CG) compared with ⁵¹Cr-EDTA. Methods: This study was carried out in 40 Caucasian older patients with advanced age (≥60) and chronic kidney disease stages 3–4. To assess the utility of prediction equations in relation to body composition, we measured lean mass (LM) with densitometry (DXA). Pearson’s, Bland-Altman and Lin’s coefficient (Rc) were used to study accuracy and precision. Results:⁵¹Cr-EDTA was 36.9 ± 9.2 ml/min/1.73 m² (22–60). Cys C levels were 2.2 ± 0.8 mg/l (r = 0.085; p = 0.662 LM) and creatinine 2.8 ± 1.1 mg/dl (r = 0.427; p = 0.021 LM). The most accurate equations were the Hoek, Larsson and Stevens formulae, with a bias of –0.2 (Rc 0.48), –2.9 (Rc 0.44) and 2.6 ml/min/1.73 m² (Rc 0.58). The biases obtained with MDRD-IDMS and CG were –14.6 (Rc 0.35) and –12.5 (Rc 0.40). All correlations among biases obtained with creatinine-based formulae and LM were negative and statistically significant (p < 0.05). Conclusions: The results show superiority of Cys C-based GFR formulae over the MDRD-IDMS and CG equations. This significant underestimation obtained with conventional prediction equations was directly related to the influence of LM.

Relationship between Body Composition and Glomerular Filtration Rate Estimates in the General Population

“…Another study carried out in Sweden [9] showed an improvement in the accuracy of eGFR when calculated lean mass was included in the prediction equation. None of these studies have employed the CKD-EPI equation and are limited to relatively small groups of patients or special populations [5,6,7,8,9,10,11,12]. Our study suggests that body composition may also be of importance in the general population but the effect may be of lesser magnitude than in these selected populations.…”

“…Several previously published studies on the relationship between muscle mass and measured GFR suggest that lean mass might influence eGFR when calculated using the MDRD equation [5,6,7,8,9,10,11,12]. For example, Macdonald et al [10] found that in non-diabetic CKD patients appendicular lean mass index explained an additional 10% of the variability in measured GFR after adjusting for creatinine, age and gender.…”

Serum Cystatin C Reflects the Progress of Albuminuria

“…Recently, cystatin C was introduced as a good marker of early renal function decline [19,20], particularly in diabetic [21] or elderly [22] patients. Cystatin C is being considered as a potential replacement for serum creatinine because it appears to be less affected by muscle mass [23], and most studies have shown that it is more highly correlated with GFR than is serum creatinine [20,24].…”