AKI is a very common disease in the setting of critical illness and carries an extremely high morbidity and mortality rate (over 50%). Currently there are no FDA approved therapeutic agents for the treatment of AKI. There is limited prospective evidence to guide nephrologists in terms of which patients will progress to more severe AKI in the setting of early AKI. Similarly, there is no evidence to guide nephrologists in terms of which patients will completely recover their renal function after AKI. Thus we need to know very early in the course of AKI which patients will progress and go on to require renal replacement therapy (RRT). Additionally we will investigating the long term patient outcomes, 2-3 years after the index AKI admission.