Utilising observational data to advance understanding of renal diseases

The prevalence of renal diseases is high and increasing worldwide. Chronic kidney disease (CKD) and acute kidney injury (AKI) are associated with reduced quality of life and poor outcomes for patients affected by these conditions while posing a significant economic burden on healthcare resources. A better understanding of the epidemiology of renal diseases is therefore an important research priority, with the objective of preventing their occurrence and progression as well as improving patient management and outcomes. This thesis focuses on a clinical topic, renal diseases, but gives a prominent place to the statistical and epidemiological methodologies used to perform each study presented. Indeed, throughout this PhD, my supervisors allowed me enough flexibility to work on what I am most passionate about: finding the most adequate and state-of-the-art epidemiological method to best answer a clinical research question. Therefore, each chapter of this thesis presents the opportunity to apply a novel epidemiological approach to high-quality patient-level routinely collected healthcare data to better understand renal diseases in four specific situations. Firstly, I explored the intersections of CKD with pain. For this purpose, I present the findings of two systematic reviews and meta-analyses. The first one establishes the prevalence of various pain types whilst the other investigates the prevalence of analgesic use and their associated adverse events, in the CKD population. I go on to explore AKI as well as acute kidney disease (AKD), which bridges the gap between AKI and CKD. The main objective of this section was to investigate the association between time to recovery from AKI and adverse outcomes. Then, as the COVID-19 pandemic commenced shortly after the beginning of my PhD, I took this opportunity to explore the association between CKD and COVID-19, focusing more specifically on cardiovascular diseases. Finally, I present a pharmacoepidemiological study conducted under the target trial emulation framework, where I aimed to assess how the treatment decision of stopping versus continuing metformin affects outcomes of patients with advanced CKD.