The goal of this observational study is to know if, in patients with acute kidney injury, naive for renal injurie, admitted to different ICUs, the change in plasma concentration of c-cistatin, between initiation and discontinuation of CRRT, is a predictive finding to optimize the withdrawal time of renal support

Inclusion Criteria:

• age ≥ 18 years;
• diagnosis of acute kidney injury (defined according to KDIGO 2012 criteria)
• need for support with CRRT according to the indications of the nephrologist consultants and Clinical Practice
• Obtaining informed consent

Exclusion Criteria:

• CRRT already ongoing (in another department not participating in the study) at the time of transfer/admission to intensive care;
• need for RRT (any type and modality) in the 14 days prior to enrolment;
• diagnosis of AKD/CKD/ESRF on admission;
• Discontinuation of CRRT under conditions that do not comply with the criteria established by the study;
• Need for CRRT not associated with AKI condition (e.g. elimination of toxicants);
• pregnant women;
• presence of known thyreopathy
• Continuous use of corticosteroids
• patient with known neoplastic disease.

The study will include all adult patients suffering from acute renal injury needing to CRRT, admitted to the enrolling centers starting from the approval of the Ethics Committee