Pre-existing iron deficiency anemia and long-term risk of recurrent acute kidney injury in survivors of ICU-associated AKI: a propensity-matched study.

Background: Recurrent acute kidney injury (rAKI) is a common complication among critically ill patients and is associated with progressive renal deterioration and increased long-term morbidity. Iron deficiency anemia (IDA) may compromise renal adaptive responses through impaired oxygen delivery and cellular energetics; however, whether pre-existing IDA is associated with rAKI risk remains unclear. Methods: We conducted a propensity score-matched retrospective cohort study using the TriNetX database (2010-2024). Adults with AKI during intensive care unit admission were stratified by pre-existing IDA status diagnosed within 6 months before the index AKI episode. A 90-day landmark approach was employed to minimize immortal-time bias. The primary outcome was rAKI occurring between 3 months and 3 years. Secondary outcomes included progression to end-stage renal disease (ESRD), all-cause mortality, major adverse cardiovascular events (MACEs), and estimated glomerular filtration rate (eGFR) decline below 30 ml/min/1.73 m Results: After matching, 13,002 individuals were included in each cohort. Pre-existing IDA was associated with a significantly higher risk of rAKI (hazard ratio [HR], 1.53; 95% confidence interval [CI], 1.44-1.63; Conclusion: Pre-existing IDA is associated with an increased risk of rAKI and accelerated renal function decline among critically ill AKI survivors. However, owing to the observational design, a causal relationship cannot be established. Prospective investigations are warranted to validate these observations and to clarify the underlying biological mechanisms.