Q & A: Low Potassium and AN

Q: I’ve heard that when treating young patients with anorexia nervosa, clinicians must be careful to avoid phosphorus deficiencies. Can you tell me what this is about?

A: You’re right to be concerned about these issues. The revised American Psychiatric Association’s Practice Guidelines for the Treatment of Patients with Eating Disorders draws specific attention to the dangers of hypophosphatemia during refeeding of patients with anorexia nervosa. During refeeding, especially in conjunction with increased rates of feeding and increased intake of carbohydrates, the body’s requirements for and utilization of phosphorus increases substantially, since phosporus is needed for increased adenosine triphosphate (ATP) related metabolic processes in cells. These requirements may result in rapid shifts of phosphorus from serum into cells, leading to deficiencies in serum, which may be accompanied by cardiac arrhythmias (sometimes sudden death), delirium and other disturbances. In large case series on adolescent inpatient units, almost 6% of patients developed moderate and about 15% mild hypophosphatemia, most notable in patients who are severely malnourished, with serum values reaching a low point during the first week of refeeding. Authorities suggest daily monitoring of serum phosphorus during the first week of refeeding with supplementation as indicated (Ornstein et al, J Adolescent Health 2003; 32: 83).

—J.Y.