Acute Kidney Injury: Pathophysiology, Classification, and Global Epidemiology: Review Article

Background: Acute kidney injury (AKI) is a sudden reduction in kidney function marked by raised serum creatinine and diminished urine output within seven days. It represents part of the broader spectrum of acute kidney diseases and disorders (AKD) and may progress to or coexist with chronic kidney disease (CKD). Objective: To provide a comprehensive review of the pathophysiology, classification, and global epidemiology of acute kidney injury. Methods: We conducted a search on Science Direct, Google Scholar and PubMed for relevant articles regarding Acute kidney injury, Epidemiology, Pathophysiology and Classification. Only the most recent or comprehensive research performed between 2018 and April 2025 was deemed. The authors assessed the value of resources culled from other works within the same genre. Documents written in languages other than English were disregarded because of insufficient translation funding. Unpublished works, conference abstracts, oral presentations, and dissertations are often considered not to constitute scientific research. Conclusion: Acute kidney injury is categorized into intrinsic, prerenal, and postrenal types depending on underlying mechanisms. Prerenal AKI caused by impaired renal perfusion, intrinsic AKI from direct parenchymal injury and postrenal AKI from urinary obstruction. The global incidence of AKI varies widely, affecting 3–20% of hospitalized cases and up to sixty-seven percent of the critically ill, with higher rates in developing countries due to preventable causes such as dehydration and infections. Despite advances, diagnosis remains largely functional, underscoring the need for early detection using emerging biomarkers to enhance results and decrease death.