Estimating Treatment Goal Weights in Adolescents With Anorexia Nervosa and Atypical Anorexia Nervosa: Comparison of the Median BMI and Historical BMI Percentile

Background

Determining an accurate treatment goal weight (TGW) is critical for treating eating disorders requiring weight restoration. This is challenging in adolescents since body mass index (BMI) normally increases over time. Median BMI (mBMI) is often used to determine TGW, though use of historical growth trajectories is increasingly common. Using the appropriate method to set TGW may be particularly important in treating individuals with anorexia nervosa (AN) whose prior growth was substantially above or below the median, and in atypical anorexia (AAN) where prior growth is, by definition, above the median.

Objectives

(1) Compare differences between TGWs based on mBMI and historical BMI percentile (hBMI) in patients with AN and AAN. (2) Determine whether either TGW method better predicted scores on the Eating Disorder Examination (EDE), heart rate, and menstrual status during treatment.

Method

Retrospective chart review of 197 adolescents with AN or AAN completing a partial hospitalization program (PHP).

Results

For AN, the within-person variation between methods varied up to 11.3 kg, though the average TGW was similar if derived from the mBMI or hBMI. In AAN, the average hBMI TGW was higher than mBMI TGW, and within-person variation was up to 19.3 kg. Associations between hBMI TGW and mBMI with heart rate, menstrual status, and EDE scores varied.

Discussion

Within-person differences in TGWs derived from hBMI versus mBMI can be large, with prominent differences in AAN, where hBMI TGW is significantly higher.