NDT Advance Access originally published online on November 6, 2008
Nephrology Dialysis Transplantation 2009 24(4):1197-1205; doi:10.1093/ndt/gfn594
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Predictivity of survival according to different equations for estimating renal function in community-dwelling elderly subjects
1 Nephrology Division, SM Annunziata Hospital, ASL 10 Florence 2 Tuscany Health Regional Agency, Florence 3 Geriatric Division, ASL 10 Florence, Italy 4 Longitudinal Studies Section, Clinical Research Branch, National Institute on Aging, Baltimore, MD, USA 5 Department of Medical and Surgical Critical Care, Multidisciplinary Centre of Research on Food Sciences (G.R.A.), University of Florence, Florence, Italy 6 Laboratory of Epidemiology, Demography and Biometry, National Institute on Aging, National Institutes of Health, Bethesda, MD, USA
Correspondence and offprint requests to: Francesco Pizzarelli, Nephrology and Dialysis Unit, SM Annunziata Hospital, via dell’Antella 58, 50011 Florence, Italy. Tel/Fax: +39-055-2496-223; E-mail: fpizzarelli{at}yahoo.com
 |
Abstract |
|---|
Background. Detection of subjects with early chronic kidney disease (CKD) is important because some will progress up to stage 5 CKD, and most are at high risk of cardiovascular morbidity and mortality. While validity and precision of estimated glomerular filtration rate (eGFR) equations in tracking true GFR have been repeatedly investigated, their prognostic performance for mortality has not been hitherto compared. This is especially relevant in an elderly population in whom the risk of death is far more common than progression.
Methods. We analysed data of participants in the InCHIANTI study, a community-based cohort study of older adults. Twenty-four-hour creatinine clearance (Ccr), Cockcroft–Gault (C-G) and Modification of Diet in Renal Disease (MDRD)-derived equations (six and four input variables) were calculated at enrolment (1998–2000), and all-cause mortality and cardiovascular mortality were prospectively ascertained by Cox regression over a 6-year follow-up.
Results. Of the 1270 participants, 942 (mean age 75 years) had complete data for this study. The mean renal function ranged from 77 ml/min/1.73 m2 by Ccr to 64 ml/min/1.73 m2 by C-G. Comparisons among equations using K/DOQI staging highlight relevant mismatches, with a prevalence of CKD ranging from 22% (MDRD-4) to 40% (C-G). Reduced renal function was a strong independent predictor of death. In a Cox model–-adjusted for demographics, physical activity, comorbidities, proteinuria and inflammatory parameters—participants with Ccr 60–90 ml/min/1.73 m2 and Ccr <60 ml/min/1.73 m2 were, respectively, 1.70 (95% CI: 1.02–2.83) and 1.91 (95% CI: 1.11–3.29) times more likely to die over the follow-up compared to those with Ccr >90 ml/min/1.73 m2. For the C-G, the group with values <60 ml/min/1.73 m2 had a significant higher all-cause mortality compared to those with values >90 ml/min/1.73 m2 (HR 2.59, 95% CI: 1.13–5.91). The classification based on the MDRD formulae did not provide any significant prognostic information. The adjusted risk of all-cause mortality followed a similar pattern when Ccr and estimating equations were introduced as continuous variables or dichotomized as higher or lower than 60 ml/min. C-G was the best prognostic indicator of cardiovascular mortality. Possibly, Ccr and C-G are better prognostic indicators than MDRD-derived equations because they incorporate a stronger effect of age.
Conclusions. In a South-European elderly population, the prevalence of CKD is high and varies widely according to the method adopted to estimate GFR. Researchers and clinicians who want to capture the prognostic information on mortality related to kidney function should use the Ccr or C-G formula and not MDRD equations. These results highlight the importance of strategies for early detection and clinical management of CKD in elderly subjects.
Keywords: Cockcroft–Gault formula; elderly; MDRD equations; mortality; population-based study
Received for publication: 28. 3.08
Accepted in revised form: 29. 9.08