Screening for eating disorders: false negatives and eating disorders not otherwise specified

Objective: To study the problem of false negatives in the screening for eating disorders. Subjects and Methods: We administered the Eating Attitudes Test (EAT40) and the Eating Disorder Inventory (EDI) to 186 Italian female students (age 17.68 +/- 0.9; BMI 20.84 +/- 2.69). Then we submitted not only high-scorers but also all the subjects to a semi-structured diagnostic interview (Eating Disorder Examination - EDE 12.0D). The diagnosis of eating disorders not otherwise specified (EDNOS) was applied to cases which met all the DSM-IV criteria for AN and/or BN with one exception. Results: 17 girls (9.1 %) fulfilled diagnostic criteria for eating disorders: I bulimia nervosa full-syndrome and 16 EDNOS. Of the 17 girls 11 were EAT low-scorers (< 30) and 8 were EDI low-scorers (< 50); 5 subjects scored below the cutoff on both instruments. We calculated sensitivity (35.3%), specificity (88.8%), positive predictive value (PPV, 24.0%) and negative predictive value (NPV, 93.2%) of the EAT40; the respective values for the EDI were 52.9% (sensitivity), 85.2% (specificity), 26.4% (PPV) and 94.7% (NPV). Discussion and conclusion: Our data show that the introduction of the EDNOS diagnoses increases the PPV of the two questionnaires but lowers their sensitivity. We conclude that using a two stage screening approach leads to a very high rate of false negatives with a significant underestimation of the prevalence of eating disorders, particularly of EDNOS.