High anion gap metabolic acidosis (HAGMA) is a frequently observed laboratory finding in critically ill patients. Usually HAGMA occurs as a result of common disease processes. However, rare diseases often manifest themselves by mimicking common disease processes with subtle differences, occasionally making the diagnosis challenging. In the following case, the metabolic workup of a patient revealed HAGMA acidosis. After ruling out the usual causes, diligent investigation by our team of subtle laboratory clues revealed a rare cause for HAGMA. © 2013 The Author(s).