CASE PRESENTATION: A 77 year old male with diabetes (last A1c 6.5), hypertension, and dementia presented to the ED with a five day history of diarrhea, vomiting, and confusion. The week prior he had been diagnosed with a urinary tract infection and was on antibiotics. Initial exam was unremarkable and vital signs were stable, however laboratory work demonstrated an elevation of creatinine to 8.8 (baseline 1.0), a pH of 7.09, a lactic acid level of 17.3 and bicarbonate level of 5. He underwent an exhaustive evaluation for causes of the renal failure, lactic acidosis, and his compensated, acute, anion gap metabolic acidosis. He was covered broadly in the event of underlying sepsis from a urinary source as well as empiric treatment Clostridium difficile infection. He rapidly improved with supportive treatment that included bicarbonate therapy. Given this improvement and the retrospective finding of a metformin level more than twice the therapeutic range, his acidosis was attributed to his continued use of metformin during an acute kidney injury from dehydration secondary to a diarrheal illness.