A 13-year-old with a history of bulimia nervosa is brought to the clinic for fatigue and irregular heartbeat. Which assessment finding would require immediate intervention?

Choice A rationale Low potassium (hypokalemia) and ECG rhythm changes, such as QT prolongation or arrhythmias, are critical and life-threatening complications of bulimia nervosa due to fluid and electrolyte imbalances from purging behaviors. Hypokalemia can directly impair cardiac function, necessitating immediate medical intervention to prevent fatal arrhythmias. Choice B rationale Erosion of dental enamel and constant vomiting are chronic manifestations of bulimia nervosa. While they indicate ongoing disordered eating and require dental intervention, they are not acutely life-threatening and do not represent the same level of immediate physiological instability as severe electrolyte imbalances affecting cardiac function. Choice C rationale Menstrual irregularities, including amenorrhea, are common in individuals with bulimia nervosa due to hormonal disruptions from malnutrition and stress. While indicative of chronic health impact, they are not an immediate life-threatening concern requiring emergency intervention compared to acute cardiac complications. Choice D rationale Calluses on knuckles (Russell's sign) and skin breakdown are physical signs of repeated self-induced vomiting. These are chronic cutaneous manifestations reflecting the mechanical trauma from purging. While they require attention, they are not acute physiological emergencies demanding immediate intervention.