Change in glomerular filtration rate over time in the Oxford Renal Cohort Study: observational study

Abstract

Background: Decline in kidney function can result in adverse health outcomes. The Oxford Renal Cohort Study has detailed baseline assessments from 884 participants ≥60 years of age.

Aim: To determine the proportion of participants with a decline in estimated glomerular filtration rate (eGFR), identify determinants of decline, and determine proportions with chronic kidney disease (CKD) remission.

Design and setting: Observational cohort study in UK primary care.

Method: Data were used from baseline and annual follow-up assessments to monitor change in kidney function. Rapid eGFR decline was defined as eGFR decrease >5 ml/min/1.73 m²/year, improvement as eGFR increase >5 ml/min/1.73 m²/year, and remission in those with CKD at baseline and eGFR >60 ml/min/1.73 m² during follow-up. Cox proportional hazard models were used to identify factors associated with eGFR decline.

Results: There was a net decline in eGFR in the 884 participants over 5 years of follow-up. In 686 participants with >2 eGFR tests with a median follow-up of 2.1 years, 164 (24%) evidenced rapid GFR decline, 185 (27%) experienced eGFR improvement, and 82 of 394 (21%) meeting CKD stage 1-4 at baseline experienced remission. In the multivariable analysis, smoking status, higher systolic blood pressure, and being known to have CKD at cohort entry were associated with rapid GFR decline. Those with CKD stage 3 at baseline were less likely to exhibit GFR decline compared with normal kidney function.

Conclusion: This study established that 24% of people evidenced rapid GFR decline whereas 21% evidenced remission of CKD. People at risk of rapid GFR decline may benefit from closer monitoring and appropriate treatment to minimise risks of adverse outcomes, although only a small proportion meet the National Institute for Health and Care Excellence criteria for referral to secondary care.

Keywords: chronic kidney diseases; cohort studies; glomerular filtration rate; primary care.

Figure 1.

Number of participants with estimated glomerular filtration (eGFR) tests at their baseline visit and subsequent eGFR tests for each year after entering the cohort.

Figure 2.

Mean estimated glomerular filtration (eGFR) for people with up to five eGFR tests (n = 884).

Figure 3.

Flowchart showing people moving across the diagnostic threshold for chronic kidney disease (CKD) for those with complete baseline and year 2 follow-up (n = 403). There were 139 participants (55%) with CKD at baseline who remained below the CKD threshold throughout follow-up at both year 1 and year 2. ^aYear 1: data for 89 participants missing.