Calculation of expected body weight in adolescents with eating disorders.

OBJECTIVE: To examine the agreement between three methods to calculate expected body weight (EBW) for adolescents with eating disorders: (1) BMI percentile, (2) McLaren, and (3) Moore methods.

METHODS: The authors conducted a cross-sectional analysis of baseline information from adolescents seeking treatment of disordered eating at The University of Chicago. Adolescents (N = 373) aged 12 to 18 years (mean = 15.84, SD = 1.72), with anorexia nervosa (n = 130), bulimia nervosa (n = 59), or eating disorder not otherwise specified (n = 184). Concurrence between the BMI percentile, McLaren, and Moore methods was assessed for agreement above or below arbitrary cut points used in relation to hospitalization (75%), diagnosis (85%), and healthy weight (100%). Patterns of absolute discrepancies were examined by height, age, gender, and menstrual status. Limitations to some of these methods allowed comparison between all 3 methods in only 204 participants.

RESULTS: Moderate agreement was seen between the 3 methods (κ values, 0.48-0.74), with pairwise total classification accuracy at each cut point ranging from 84% to 98%. The most discrepant calculations were observed among the tallest (>75th percentile) and shortest (<20th percentile) cases and older ages (>16 years). Many of the most discrepant cases fell above and below 85% EBW when comparing the BMI percentile and Moore methods, indicating disagreement on possible diagnosis of anorexia nervosa.

CONCLUSIONS: These methods largely agree on percent EBW in terms of clinically significant cut points. However, the McLaren and Moore methods present with limitations, and a commonly agreed-upon method for EBW calculation such as the BMI percentile method is recommended for clinical and research purposes.