NDT Advance Access originally published online on January 26, 2008
Nephrology Dialysis Transplantation 2008 23(5):1770-1771; doi:10.1093/ndt/gfm944
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Relative mortality risk in chronic kidney disease and end-stage renal disease: the effect of age, sex and diabetes
Correspondence and offprint requests to: E-mail: emmanuel.villar{at}chu-lyon.frSir,
We read with great interest the article by Raymond et al., published in the November issue of the journal [1]. In a large population-based study in the UK, the authors explored the excess mortality in patients with chronic kidney disease (CKD) against a reference population with an estimated glomerular filtration rate (eGFR) over 60 mL/min, by CKD stage and by age-band. One of the main results was that excess mortality decreased when subject age increased in each CKD stage.
This expected result is consistent with the findings of our team in a regional end-stage renal disease (ESRD) population in France [2]. This result is expected, because in the adult general population, mortality rates are lower in younger subjects and increase with age (as shown in Table 3 of the paper [1]). But the health gap and the absolute mortality risk gap between a population with a given chronic disease and the general population narrow down when age increases. This leads to a ‘natural’ decrease in a mortality ratio when age increases, as shown for an example in the obese population [3].
Moreover, assessment of excess mortality is usually performed with standardized mortality ratios (SMR) developed by Breslow and Day [4]. Ratios should be at least standardized for age and for gender [4], and should take into account actual lengths of subject observation [2,4].
Beyond the methodological issue, adjustment for gender is clinically relevant because mortality rates are lower in females in the general population in each age-band [5]. As in younger patients, SMR were significantly higher in ESRD female patients than in males [2]: ESRD cancelled out the female survival advantage observed in the general population.
Excess mortality in diabetics with CKD is another key issue. In the ESRD population, age- and gender-SMR were higher in patients with diabetic nephropathy than in patients with other nephropathies [2]. SMR gap between female and male was also higher in patients with diabetic nephropathy [2]. This interaction between gender and diabetes was confirmed in the Australia and New Zealand ESRD population [6]. The question raised by these results is the comparison of the effect of ESRD and CKD in diabetes and in non-diabetes populations with computation of age-, gender- and diabetes status-SMR.
In Raymond et al.'s population-based cohort, age, gender, diabetes status, eGFR and mortality rates are available data [1]. Additional analyses by gender and by diabetes status could therefore usefully improve the knowledge of interactions between age groups, genders and diabetes in CKD population mortality.
Conflict of interest statement. None declared.
Hospices Civils de Lyon, Department of Nephrology and Renal Transplantation, Lyon-Sud Academic Hospital, Pierre-Benite, France
References
- Raymond NT, Zehnder D, Smith SCH, et al. Elevated relative mortality risk with mild-to-moderate chronic kidney disease decreases with age. Nephrol Dial Transplant (2007) 22:3214–3220.
[Abstract/Free Full Text] - Villar E, Remontet L, Labeeuw M, et al. Effect of age, sex and diabetes mellitus on excess death in end-stage renal failure. J Am Soc Nephrol (2007) 18:2125–2134.
[Abstract/Free Full Text] - Bender R, Jockel KH, Trautner C, et al. Effect of age on excess mortality in obesity. JAMA (1999) 281:1498–1504.
[Abstract/Free Full Text] - Breslow NE, Day NA. Statistical Methods in Cancer Research. Volume II—The Design and Analysis of Cohort Study (1987) 82. Lyon, France: International Agency for Research on Cancer, Scientific Publication. 65–99.
- Trovato F, Heysen NB. A varied pattern of change of the sex differential in survival in the G7 countries. J Biosoc Sci (2006) 38:391–401.[CrossRef][Web of Science][Medline]
- Villar E, Chang SH, McDonald SP. Incidences, treatments, outcomes, and sex effect on survival in patients with end-stage renal disease by diabetes status in Australia and New Zealand (1991–2005). Diabetes Care (2007) 30:3070–3076.
[Abstract/Free Full Text]
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Editorial Note: Dr Raymond et al were invited to respond to this letter but we did not receive their reply.
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