Hyperphosphatemia: an objective marker for bulimia nervosa?

Phosphorus abnormalities among patients suffering from eating disorders, although cited, have received relatively little attention. Studies generally report decreased concentrations of phosphorus for both bulimia and anorexia nervosa. We have recently noted hyperphosphatemia in several consecutive hospitalized bulimic patients who appeared to have normal renal function and calcium levels. Case files of 30 inpatient and outpatient female bulimic patients and 30 sex- and age-matched physically healthy psychiatric inpatients and outpatients were reviewed. Phosphorus and electrolytes related to phosphorus metabolism were compared between the two groups. Twenty-four of 30 bulimic patients (80%) were found to have at least one elevated serum phosphorus concentration, whereas all but one of 30 age-matched controls had values within normal limits. Elevated phosphorus levels were generally in the mild to moderate range. No correlation was found between phosphorus levels and any of the other electrolytes examined in both patients and controls. No correlation was found between phosphorus levels and the reported frequency of bingeing and vomiting or the number of laxatives ingested. Since bulimic patients are generally of normal weight and tend to deny their disturbed eating habits, diagnosis is often delayed. However, bulimia may be suspected from biochemical abnormalities such as hypokalemia, hypochloremia, elevated amylase, and acid-base disturbances. This preliminary study indicates that elevated serum phosphorus levels may serve as an additional objective marker for the presence of bulimia nervosa.