Acute kidney phenotypes in France: nationwide annual first-hospitalization rates and phenotype-specific epidemiology from administrative health data

BACKGROUND: Acute kidney phenotypes are a major cause of hospitalization, but nationwide data on their hospitalization rates and sociodemographic characteristics are limited. We conducted a nationwide hospitalization-based study of acute kidney phenotypes identified from administrative health data in France. METHODS: We performed a nationwide study using data from the French National Health Data System between 2019 and 2021. Hospitalizations with a principal discharge diagnosis corresponding to one of four acute kidney phenotypes - acute kidney injury (AKI), glomerulopathy, tubulointerstitial/acute pyelonephritis (TIN/AP), or nephrolithiasis - collectively referred to as acute kidney phenotypes (AKP) were identified in the French national hospital discharge database using International Classification of Diseases, 10th Revision (ICD-10) codes. Annual first-hospitalization rates were age and sex-standardized to the 2021 French population and expressed per 1,000,000 inhabitants with 95% confidence intervals (CIs). RESULTS: Among 624,130 patients hospitalized with an AKP, nephrolithiasis accounted for 49.8% of cases, TIN/AP for 34.2%, AKI for 12.3%, and glomerulopathy for 3.7%. Age- and sex-standardized annual first-hospitalization rates (per 1,000,000 inhabitants) by phenotype are reported for each calendar year. For glomerulopathy, rates were 132 (95% CI 130-135) in 2019, 115 (112-117) in 2020 and 116 (113-119) in 2021. AKI rates were 428 (423-433) in 2019, 409 (404-414) in 2020 and 428 (423-433) in 2021. Nephrolithiasis rates were 1,782 (1,772-1,792), 1,700 (1,690-1,710) and 1,737 (1,727-1,746), respectively. TIN/AP rates were 1,162 (1,154-1,170) in 2019, 1,063 (1,055 - 1,071) in 2020 and 1,039 (1,031 - 1,047) in 2021. TIN/AP showed a bimodal age distribution (20.3% <10 years; 27.3% ≥80 years) and a marked female predominance (73.5%), consistent with the predominance of acute pyelonephritis within this claims-based phenotype (84%). CONCLUSION: This nationwide study provides the first hospitalization-based estimates of four acute kidney phenotypes in France and highlights distinct epidemiological profiles across subtypes. These findings support targeted prevention and monitoring of high-risk patients and provide a framework for future pharmacoepidemiological studies of drug-associated nephrotoxicity.