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.