Background: Cardiac‑surgery‑associated acute kidney injury (CSA‑AKI) is a frequent postoperative complication worldwide and is associated with increased mortality, prolonged intensive care unit stay, and substantial resource utilization. While reported incidence appears broadly similar across high‑income countries (HICs) and low‑ and middle‑income countries (LMICs), emerging evidence suggests marked disparities in severity at presentation and clinical outcomes.

Objectives: To compare the epidemiology, severity, outcomes, and health‑system determinants of CSA‑AKI across HIC and LMIC settings, and to identify system‑level contributors to excess mortality in resource‑limited environments.

Methods: We conducted a focused narrative review of contemporary observational studies reporting CSA‑AKI incidence, severity, renal replacement therapy (RRT) utilization, and mortality following adult cardiac surgery. Literature was identified through targeted searches of PubMed/MEDLINE and hand‑searching of reference lists. Priority was given to studies using standardized AKI definitions (RIFLE, AKIN, or KDIGO) and reporting clinically relevant perioperative outcomes.

Findings: Across income settings, CSA‑AKI incidence ranged from approximately 20% to 43%. However, LMIC cohorts consistently demonstrated more advanced AKI at diagnosis and substantially higher AKI‑associated mortality, particularly among patients requiring RRT. In HICs, dialysis‑requiring CSA‑AKI was uncommon (~1%) but carried high mortality despite early detection and unrestricted access to renal support. In contrast, LMIC settings reported lower RRT utilization, delayed initiation, and mortality exceeding 40–55% in advanced AKI stages.

Conclusions: CSA‑AKI is a common global complication of cardiac surgery with disproportionately severe consequences in resource‑limited settings. Excess mortality in LMICs appears largely driven by delayed detection and constrained rescue capacity rather than biological susceptibility alone. Strengthening perioperative surveillance and access to timely renal support may substantially reduce avoidable mortality.