A 16-year-old boy is brought to the emergency department after a car accident. Physical examination shows left-sided flank tenderness and a fracture of the left tibia. Vitals are within normal limits. Which of the following is the most appropriate next step in diagnosis?
Measurement of blood urea nitrogen
Measurement of serum creatinine
Urinalysis for blood
Urinalysis for casts
Urinalysis for protein
