Sensitivity and specificity of the Quetelet index to assess obesity in men and women.

Objective and Methods: In a cross-sectional design, the sensitivity and specificity of the Quetelet Index (QI) was determined in relation to percent body fat standards. Subjects were 1280 men and 365 women asymptomatic for coronary heart disease. Contingency tables by QI quartiles were created using two sets of criteria of obesity: body fat > or = 25% and QI > or = 28 kg.m-2 for men and 30% and 27 kg.m-2 for women. Percent body fat was determined with hydrodensitometry in all subjects.
Results: In men, sensitivity, positive, and negative predictive value of QI in relation to percent body fat was 54.5%, 91.8%, 82.7% and 73.8%, respectively. The corresponding values for women were 26.9%, 98.2%, 90.7% and 67.1%. Sensitivity of QI was 2.03 times greater for men than for women (P < 0.001). Receiver operator characteristic (ROC) curve analysis suggested that an acceptable trade-off between sensitivity (91%) and specificity (47%) occurred at a QI of 24.5 kg.m-2 for men and at a QI of 22 kg.m-2 for women.
Conclusions: The data suggest that in an asymptomatic population, percent body fat-based QI cut-off values may misclassify the obese. A fat mass-based reference system could perhaps lead to an improved classification outcome.