Q J Med 2004; 97:365–376 doi:10.1093/qjmed/hch064 Masterclasses in medicine An unusual cause for ketoacidosis M.R. DAVIDS 1 , A.S. SEGAL 2 , H. BRUNENGRABER 3 and M.L. HALPERIN 4 From the 1 Nephrology Unit and Department of Internal Medicine, University of Stellenbosch, Cape Town, South Africa, 2 Division of Nephrology, University of Vermont, Burlington, USA, 3 Department of Nutrition, Case Western Reserve University, Cleveland, USA, and 4 Division of Nephrology, St Michael’s Hospital, University of Toronto, Toronto, Canada Summary A 22-year-old male developed a severe degree of metabolic acidosis (plasma pH 7.20, bicarbonate 8 mmol/l), with a large increase in the plasma anion gap (26 mEq/l). Ketoacidosis was suspected because of the odour of acetone on his breath and a positive qualitative test for acetone in plasma (to a 1:4 dilution). Later, his plasma b-hydroxy- butyrate concentration was found to be 4.5 mmol/l. After receiving an infusion of 1 l of half-isotonic saline and 1 l of 5% dextrose in water over 24 h, as well as curtailing his large oral intake of sweetened beverages, all blood tests became normal. Diabetic ketoacidosis, alcoholic ketoacido- sis, starvation ketosis and hypoglycaemic ketoaci- dosis were all ruled out, and his toxin screen was negative for salicylates. Finding another pos- sible cause for ketoacidosis became the focus of this case. Introduction In our continuing series on the application of prin- ciples of integrative physiology at the bedside, once again the central figure is an imaginary consultant, the renal and metabolic physiologist, Professor McCance, who deals with data from a real case. On this occasion his colleague Sir Hans Krebs, an expert in the field of glucose and energy metabo- lism, assists him in the analysis. Their emphasis is on concepts that depend on an understanding of physiology that crosses subspecialty boundaries. To avoid overwhelming the reader with details, key facts are provided, but only when necessary. The overall objective of this teaching exercise is to demonstrate how application of simple princi- ples of integrative physiology at the bedside can be extremely helpful for clinical decision-making (Table 1). The consultation The housestaff were stumped by this perplexing case (more complete information is provided in Appendix 1 and Table 2). They were evaluating a patient who had metabolic acidosis accom- panied by a large increase in the plasma anion gap (Table 3). Because of the odour of acetone on his breath and a positive test for plasma ketones, he appeared to have ketoacidosis. However, try as they might, the data did not fit into any of the entities in their differential diagnosis of ketoacidosis (Table 3). The next step was obvious: seek a consultation with Professor McCance. As the intern began to present the patient’s history and physical findings, Professor McCance stopped her. He wanted only the most important data Address correspondence to Professor M.L. Halperin, St. Michael’s Hospital Annex, Lab #1, Research Wing, 38 Shuter Street, Toronto, Ontario, M5B 1A6, Canada. e-mail: mitchell.halperin@utoronto.ca QJM vol. 97 no. 6 ! Association of Physicians 2004; all rights reserved.