OBJECTIVE: The literature on the prevalence and importance of
hypokalemia in persons with eating disorders in contradictory and
confusing. The authors investigated the frequency of hypokalemia and its
relationship to symptoms in a group of outpatients with eating disorders.
METHOD: Diagnostic evaluations and electrolyte studies were performed for
945 outpatients meeting the DSM-III-R criteria for eating disorders at the
time of their intake evaluations at a suburban clinic for eating disorders.
RESULTS: Clinically significant hypokalemia was comparatively rare. A total
of 43 subjects (4.6%) were hypokalemic; of these, seven (0.7% of all
subjects) were borderline hypokalemic (serum potassium = 3.4 mmol/liter).
The hypokalemic subjects had a significantly lower mean weight and body
mass index at entry than the normokalemic subjects. Significantly more of
the hypokalemic subjects purged by abusing laxatives, either alone or with
vomiting. The patients with restricting (nonpurging) anorexia nervosa, even
those whose weights were very low, were generally normokalemic.
CONCLUSIONS: The low frequency of hypokalemia in this group of eating
disordered outpatients suggests that routine electrolyte determination is a
poor screening tool for occult or denied bulimia. Hypokalemia occurred
almost invariably in lower-weight bulimic (or anorectic/bulimic) patients
who were vomiting and/or abusing laxatives. Indeed, the study suggests that
hypokalemia in a patient with an eating disorder is virtually certain
evidence that the patient is purging at least daily. In addition, it
appears that a patient with purely restricting anorexia nervosa is not at
risk for hypokalemia even if his or her weight is very low.