Sensitivity and specificity of different classification criteria for excess weight in schoolchildren from Joao Pessoa, Paraiba, Brazil

Objective The objective of this study was to describe the proportion of excess weight using different body mass index classification criteria and assess the sensitivity, specificity, and agreement among the criteria. Methods The population included 1,570 students, aged 7-12 years, of the city of Joao Pessoa (PB), in 2005. Excess weight was classified according to the World Health Organization, International Obesity Task Force criteria and other criteria. The percentage of body fat was estimated from skinfold thickness measurements and used as reference criteria (>= 25% in males and >= 30% in females). Results The proportion of excess weight differed among the different classification systems. It was lower according to the World Health Organization criteria than to Brazilian authors' criteria (p<0.05). Body mass index classification criteria presented high sensitivity (83-97%), except for the classification proposed by the World Health Organization (65% in males and 48% in females). The specificity was high for all the analyzed criteria (85-98%). The Kappa index showed good agreement among the criteria, with a small increase for the International Obesity Task Force criteria (Kappa=0.72) and smaller agreement for the World Health Organization criteria (Kappa=0.63). Conclusion The analyzed criteria were sensitive for the detection of excess weight, but the World Health Organization criteria were less sensitive. There was high specificity and agreement among the criteria; however, the values obtained for the different genders and ages varied less when the International Obesity Task Force criteria were used. Thus, the results suggest that the International Obesity Task Force criteria are more appropriate for the determination of excess weight in similar populations.