CST3 and acute kidney injury: There is a need for replication of the most promising surrogate markers (timed UO, creatinine clearance) or novel kidney biomarkers (serum cystatin C and NGAL) in larger prospective randomized trials of selected ICU patients with a high pre-test probability of renal recovery (normal pre-AKI eGFR, no pre-existing proteinuria, low burden of co-morbid disorders).