A 54-year old male developed end-stage renal disease secondary to diabetes. He received a kidney transplant from a living relative. The transplant functioned well with significant improvement in his well being. However, 4 months after transplantation, he noticed tenderness in his groin over the site of transplant, fever, malaise, oliguria, and decreased urine output. Which of the following is the most valuable prognostic indicator in this patient?
