The incidence of acute kidney injury (AKI) has increased in the recent past. Patients with AKI have an increased risk of mortality. They are also at increased risk of developing chronic kidney disease (CKD). AKI can lead to irreversible loss of renal function despite complete clinical recovery. Currently, no tools are available to diagnose this subclinical loss of renal function. Renal functional reserve (RFR) can serve as an essential tool for analyzing this subclinical loss of renal function, and patients with loss of RFR post-AKI may be closely followed for the development of CKD. This prospective observational study, conducted at the Department of Nephrology, Jawaharlal Institute of Postgraduate Medical Education & Research (JIPMER), aimed to investigate RFR in 223 patients with AKI requiring dialysis. The study excluded patients with CKD and obstructive uropathy. Methods included RFR assessment three months post-AKI recovery, utilizing technetium-99m (Tc-99m) diethylenetriaminepentaacetic acid (DTPA) plasma clearance during amino acid infusion. Statistical analyses and logistic regression were applied, receiving ethical approval. Results revealed a high in-hospital mortality rate of 78.02%, associated with elevated Sequential Organ Failure Assessment (SOFA) scores. Among 24 patients with complete AKI recovery, the RFR at three months was 10.06% (interquartile range (IQR) 5.60-20.15), with the measured GFR significantly lower than the estimated glomerular filtration rate (GFR). The study concludes that AKI requiring dialysis is linked to high mortality and emphasizes the predictive value of SOFA scores. Additionally, RFR testing at three months post-recovery provides insights into potential long-term impacts on renal function. This study contributes valuable insights into the prognosis of AKI patients requiring dialysis. It underscores the need for further research on RFR as a diagnostic tool and the lasting consequences of AKI.