%0 Case Reports %T A case of spontaneous tumor lysis syndrome in an adolescent with abdominal pain. %A Osborne KD %A Osborne KC %A Bedard PJ %J Am J Emerg Med %V 73 %N 0 %D 2023 Nov 1 %M 37734989 %F 4.093 %R 10.1016/j.ajem.2023.08.044 %X Tumor lysis syndrome (TLS) is an acutely life threatening, must-not miss, oncological emergency that infrequently presents to the emergency department (ED). This diagnosis is typically a complication of chemotherapy, however, TLS can also occur spontaneously as the first presentation of malignancy. This case discusses the rare presentation of an otherwise healthy adolescent male who presented to the ED with abdominal pain and lethargy and was subsequently found to be in acute renal failure and pancytopenic with the associated lab derangements of hyperkalemia, hyperphosphatemia, and hypocalcemia. Subsequent investigation revealed profound hyperuricemia, from which the presumptive diagnosis of spontaneous TLS was made. Further workup revealed the diagnosis of pre-B cell acute lymphoblastic leukemia. This case emphasizes the consideration of TLS as a cause of acute renal failure or severe electrolyte derangements in those who may not have a known diagnosis of malignancy or recent chemotherapy.