Assessing the impact of chronic kidney disease on individuals and populations: use of relative and absolute measures.

Chronic kidney disease (CKD) is now recognized as a global public health problem, contributing substantially to the burden of non-communicable disease (NCD) [1, 2]. CKD is associated with a variety of NCD outcomes, including renal [end-stage renal disease (ESRD)], cardiovascular and noncardiovascular. It is important to quantify the risks associated with CKD on such disease outcomes in individuals and the impact of CKD on whole populations, and given the high prevalence of CKD and increased risks of most NCDs at older ages, how the impact of CKD varies by age. The paper by Marks et al. is a population-based study using routinely collected data in the Grampian region of Scotland which aimed to determine the effect of CKD (largely Stage 3b–5) on renal replacement therapy (RRT) and all-cause mortality (ACM). The impact of CKD on RRT and ACM was mainly due to CKD in older age groups, a paradox given that the absolute risk of progression to RRT in the CKD cohort and the relative risks of ACM associated with CKD both fell with age. The findings are firstly an illustration of the contrasting information provided by relative and absolute measures of the effects of risk factors, age and CKD on disease outcomes, and secondly highlight the possible interaction between age and CKD. The authors also developed risk prediction tools to determine the absolute risk of RRT and ACM for patients with CKD. This article considers these concepts in more detail.