This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Kidney, Subject name: Medicine
Definition of Acute kidney injury include 
Select and explain. 
A. Increase of serum creatinine by 1mg/dl in 24 hours, B. BUN/Creatinine ratio above 20, C. Urine output less than 1000ml in a day, D. 50% increase in baseline serum creatinine in a week
D: 50% increase in baseline serum creatinine in a week
Answer: D: 50% increase in baseline serum creatinine in a week 
Explanation: AKI is currently defined by a rise of serum creatinine from baseline by at least 0.3 mg/dL within 48 h or at least 50% higher than baseline within 1 week, or a reduction in urine output to less than 0.5 mL/kg per hour for longer than 6 h. Ref: Harrison 19e pg: 1800