An adolescent has been treated for bulimia for the past 3 months and presents for a follow-up visit. To determine if the adolescent is still purging, the nurse practitioner should order.

Rationale: A. Hematocrit and hemoglobin can indicate anemia but do not reliably reflect ongoing purging behaviors. B. Serum albumin levels assess nutritional status but are not specific for detecting purging. C. Bicarbonate and sodium levels may be affected by purging, but they are less sensitive indicators than electrolyte disturbances. D. Serum potassium, chloride, and magnesium levels are commonly depleted in adolescents who continue purging through vomiting or laxative use. Monitoring these electrolytes helps detect ongoing purging behavior and prevent potentially life-threatening complications such as cardiac arrhythmias.