Kidney transplantation is the gold-standard therapy for end-stage renal disease. However, in the early postoperative period following allograft kidney transplantation, insufficient graft function presents a diagnostic challenge to clinicians. Ischemic damage to the graft and/or an early autoimmune rejection may cause a decrease in function. Ischemic damage is a benign and transient condition, while acute immune rejection requires immediate therapy. A kidney graft ultrasound may produce a false negative result, and graft biopsy is invasive and slow to return results. Serum lactate dehydrogenase (LDH) is under examination as a possible tool for differential diagnosis between ischemic damage and immune rejection. Herein, we analyze the continuous lab results of four patients in the early post-transplantation period, showing patterns correlating with different clinical outcomes and prognoses. In our experience, a persistent elevated LDH accompanies ischemic damage. Immune rejection was, however, associated with a decrease in LDH. Hemodialysis was not a confounding factor, while packed red blood cell transfusion caused severe diagnostic problems.