Acute Kidney Injury (AKI) is a common and serious condition in hospitalized patients, especially when it reaches stages 2 or 3 according to the KDIGO classification. These severe forms are associated with high mortality, a risk of progression to chronic kidney disease (CKD), and frequent cardiovascular complications. However, current data on how nephrologists manage these patients during hospitalization-and how these practices influence long-term outcomes-are limited and heterogeneous.

The FAKIR study (French AKI Registry) is a prospective, multicenter, non-interventional observational study designed to describe the clinical management of patients admitted to nephrology departments for AKI stage 2 or 3 and to assess their renal and cardiovascular outcomes up to one year. The study hypothesizes that better characterization of in-hospital practices and patient trajectories will help identify predictors of renal recovery, progression to end-stage renal disease, and major cardiovascular events.

Patients will be followed during hospitalization and at 3, 6, and 12 months to assess renal function, mortality, cardiovascular events, and rehospitalizations. This registry aims to provide real-life, multicenter data to support future guidelines and the development of structured post-AKI care pathways.

Inclusion Criteria:

• Age ≥ 18 years at admission
• Hospitalized in a nephrology ward (standard or intensive nephrology care unit)
• Diagnosis of acute kidney injury (AKI) stage 2 or 3 according to KDIGO criteria at the time of admission
• Availability of follow-up data at 3 months (clinical or laboratory)

Exclusion Criteria:

• AKI stage 1 only
• AKI acquired outside the nephrology department without subsequent transfer to nephrology
• Hospitalized for another reason without documented AKI stage 2 or 3
• Refusal or opposition to data reuse for research purposes
• Under legal protection (guardianship or trusteeship) without a representative to provide non-opposition
• Incomplete medical records preventing collection of required baseline data

The study population consists of adult patients (≥18 years) hospitalized in nephrology departments across multiple French university hospitals for acute kidney injury (AKI) stage 2 or 3. Patients are identified prospectively at the time of admission to nephrology units, either directly or via transfer from emergency or other hospital departments. Only patients with confirmed KDIGO stage 2 or 3 AKI at admission are included. Data are collected during hospitalization and up to 12 months post-discharge to assess renal and cardiovascular outcomes.