Despite progress in the recognition and harmonization of definitions of acute kidney injury (AKI),1 the importance of transient changes in serum creatinine levels continues to be controversial.2-5 The recent KDIGO (Kidney Disease: Improving Global Outcomes) creatinine-based criteria for AKI define stage 1 as an increase in serum creatinine level by 0.3mg/dL over 48 hours or by 50% over 7 days,1 though some argue that this degree of change could reflect laboratory error or biological variability rather than true kidney injury.