Fluctuations in Serum Creatinine Levels During Hospitalization and Long-Term End-Stage Kidney Disease and Mortality

Importance Acute kidney injury is associated with poor outcomes, but the clinical implication of reversible serum creatinine level fluctuations during hospitalization not necessarily defined as acute kidney injury is poorly understood. Objective To investigate the long-term outcomes of patients without previously diagnosed kidney disease who present with decreased kidney function and are subsequently discharged with apparently normal kidney function. Design, Setting, and Participants A retrospective cohort study was conducted of patients hospitalized in a large tertiary hospital in Israel between September 1, 2007, and July 31, 2022. The study included patients admitted to an internal medicine ward. Patients had not undergone dialysis during the index hospitalization, had at least 3 creatinine tests performed during hospitalization, and had a discharge estimated glomerular filtration rate (eGFR) exceeding 60 mL/min/1.73 m 2 . Patients with preexisting chronic kidney disease were excluded. Exposure Glomerular filtration rate was estimated from serum creatinine values using the updated 2022 Chronic Kidney Disease Epidemiology Collaboration formula, and eGFR greater than 60 mL/min/1.73 m 2 was regarded as normal. Exposure was defined based on the association between the first and last values determined during hospitalization. Main Outcomes and Measures All-cause mortality in the year following the index hospitalization and end-stage kidney disease (ESKD) in the 10 years following the index hospitalization. Results A total of 40 558 patients were included. Median age was 69 (IQR, 56-80) years, with 18 004 women (44%) and 22 554 men (56%). A total of 34 332 patients (85%) were admitted with a normal eGFR and 6226 (15%) with decreased eGFR. Patients with decreased eGFR on presentation had an 18% increased mortality in the year following hospitalization (adjusted hazard ratio [AHR], 1.18; 95% CI, 1.11-1.24) and a 267% increased risk of ESKD in the 10 years following hospitalization (AHR, 3.67; 95% CI, 2.43-5.54), despite having been discharged with apparently normal kidney function. The highest risk was noted in patients who presented to the hospital with an eGFR of 0 to 45 mL/min/1.73 m 2 . Conclusions and Relevance The findings of this cohort study suggest that patients who present with decreased kidney function and are discharged without clinically evident residual kidney disease may be at increased long-term risk for ESKD and mortality.