# Impact of Different CKD Definitions on Long-Term Renal Function and Mortality in a Population-Based Cohort Study

## TL;DR

This study compares different ways to define chronic kidney disease and finds that adjusting for age or body size doesn't improve predictions of kidney decline or mortality.

## Contribution

The study evaluates the impact of age- and body surface area-adjusted CKD definitions on long-term outcomes in a general population.

## Key findings

- Age-stratified CKD definitions reclassified younger adults as CKD without adverse outcomes.
- CKD groups had consistently worse outcomes regardless of definition used.
- Adjusting for age or body surface area did not improve prediction of renal decline or mortality.

## Abstract

The adoption of age or individualized body surface area (i-BSA) estimated glomerular filtration rate (eGFR) thresholds could influence the prevalence and prognosis of chronic kidney disease (CKD). This longitudinal study with up to 15 years of follow-up in the general population, compares different eGFR thresholds for CKD definition: standard, corrected to i-BSA, and age-stratified. For each, we assessed the prevalence of CKD and the combined impact on rapid renal function decline (RRFD) and mortality.

Patients were classified as CKD according to the presence of significant albuminuria and/or different eGFR thresholds as follows: (i) < 60ml/min per 1.73 m2; (ii) < 60ml/min corrected to i-BSA; (iii) stratified by age, that is, < 75, < 60 and < 45 ml/min per 1.73 m2 if aged < 40 years, 40 to 65 years, and > 65 years, respectively. We performed adjusted Cox regression analyses to predict RRFD and global mortality.

We analyzed 4952 participants (54% women; mean age: 52 years). Age-stratified definition resulted in 24 of 677 participants aged < 40 years reclassified as CKD, with no adverse outcomes; whereas 55 of 713 participants aged > 65 years were reclassified as non-CKD, with 12 deaths and 1 RRFD. After multivariate adjustment, the CKD group had a poorer prognosis compared with the non-CKD group independently of the definition used; hazard ratio (HR) and 95% confidence interval (CI) were 2.23 (1.59–3.12), 2.06 (1.46–2.90), and 1.64 (1.13–2.38) for the standard, corrected to i-BSA, and age-stratified definitions, respectively.

In our study, classification of CKD by age or i-BSA does not appear to improve prediction of RRFD and mortality.