[Body mass index: sensitivity and specificity].

Introduction: Self-reported height and weight data have been used in several studies with the purpose of determining the prevalence of overweight and obesity. Despite being a simple methodology, little information exists about the reliability of these measures, namely, in university students. The objective of this study was to determine the sensitivity and specificity of self-reported body mass index (BMI) to evaluate the prevalence of overweight and obesity in university students.

Methods: In a convenience sample of 380 university students (226 women and 154 men), weight and height were obtained by self-reported measures and anthropometric assessment according to international standards methodology (objective). BMI was calculated from self-reported and direct measures.

Results: The discrepancy between objective and self-reported weight was not significative. For height, this discrepancy was significantly different in women, in men, and between genders. The difference between BMI values was significantly different in women (0.8 +/- 1.1 kg/m2), in men (0.4 +/- 1.1 kg/m2) and between genders. Concerning overweight and obesity, according to the objective BMI, the sensitivity was only 50% in women, and 70% in men, while the specificity was 99% in women and 98% in men.

Conclusion: Our results show a poor sensitivity of self-reported weight and height data, to estimate overweight and obesity, thus, this method might not be reliable for studies of prevalence of obesity in this population.