Revista Adolescência e Saúde

Revista Oficial do Núcleo de Estudos da Saúde do Adolescente / UERJ

NESA Publicação oficial
ISSN: 2177-5281 (Online)

Vol. 14 nº 4 - Oct/Dec - 2017

Original Article Imprimir 

Páginas 113 a 120


Concordance between international parameters for assessing body mass index in adolescents

Concordancia entre parámetros internacionales para evaluar el índice de masa corporal en adolescentes

Concordância entre parâmetros internacionais para avaliar o índice de massa corporal em adolescentes

Autores: Karoline Teixeira Passos de Andrade1; Rodrigo Cappato de Araújo2; Ana Carolina Rodarti Pitangui3

1. Specialization in Sports Nutrition at Santa Fé College, São Luís, MA, Brazil.Bacharel in Nutrition, Department of Nutrition, University of Pernambuco (UPE). Petrolina, PE, Brazil
2. Doctor in Mechanical Engineering from the Federal University of Minas Gerais (UFMG). Belo Horizonte, MG, Brazil. Associate Professor of Physical Therapy and Associated Post-Graduate Program in Physical Education UPE / UFPB - University of Pernambuco (UPE). Petrolina, PE, Brazil
3. Ana Carolina Rodarti Pitangui: PhD in Sciences from the University of São Paulo (USP). Ribeirão Preto, SP, Brazil. Adjunct Professor of the Physical Therapy Course and the Graduate Program in Nursing UPE / UEPB - University of Pernambuco (UPE). Petrolina, PE, Brazil

Correspondência:
Ana Carolina Rodarti Pitangui
Universidade de Pernambuco, Campus Petrolina, Departamento de Fisioterapia
BR 203, Km 2, s/n, Vila Eduardo
Petrolina, PE, Brasil. CEP: 56328-903.
carolina.pitangui@upe.br

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Keywords: Adolescent health, body weight, body mass index, anthropometry, nutrition assessment.
Palabra Clave: Salud del adolescente, peso corporal, índice de masa corporal, antropometría, evaluación nutricional.
Descritores: Saúde do adolescente, peso corporal, índice de massa corporal, antropometria, avaliação nutricional.

Abstract:
OBJECTIVE: Verify the agreement between the BMI (body mass index) evaluation criteria proposed by the Center for Disease Control and Prevention (CDC) and the International Obesity Task Force (IOTF) in adolescent students in the city of Petrolina - PE.
METHODS: 1169 adolescent students participated in the study, 660 females and 509 males with ages between 12 to 17 years. It was measured the body mass and height, and BMI was calculated according to the parameters of the CDC and IOTF. Two types of analysis were adopted, one using four rating groups (underweight, normal weight, overweight and obesity) and another using two groups (with and without overweight). The agreement between the two parameters was assessed using the Kappa index.
RESULTS: The prevalence of overweight was 15.3% according to the CDC and 15.9% according to the IOTF. The Kappa index ranged from good (k = 0.75) for the four groups and very good (k = 0.92) for the two groups.
CONCLUSION: The BMI in the sample was similar between the applied parameters and they showed high agreement, especially when the goal is overweight detection in this population.

Resumen:
OBJETIVO: Verificar la concordancia entre los criterios de evaluación de IMC (Índice de Masa Corporal) propuestos por el Centro de Control y Prevención de Enfermedades (CDC) y por la Fuerza Tarea Internacional de Obesidad (IOTF) en adolescentes escolares del municipio de Petrolina - PE.
MÉTODOS: Participaron 1169 escolares, siendo 660 del sexo femenino y 509 del sexo masculino con edades entre 12 y 17 años. Fueron confirmadas masa corporal y estatura, y el IMC fue calculado de acuerdo a los parámetros del CDC y IOTF. Dos formas de análisis fueron adoptadas, siendo una utilizando cuatro grupos de clasificación (bajo peso, eutrofia, sobrepeso y obesidad) y otra empleando dos grupos (con y sin exceso de peso). La concordancia entre los parámetros fue evaluada por medio del índice Kappa.
RESULTADOS: La prevalencia de exceso de peso fue de 15,3% de acuerdo con el CDC y 15,9% de acuerdo con el IOTF. El índice Kappa varió de bueno (k=0,75) para cuatro grupos a muy bueno (k=0,92) para dos grupos.
CONCLUSIÓN: El IMC en la muestra fue similar entre los parámetros aplicados y los mismos presentaron alta concordancia, principalmente cuando el objetivo es detección de exceso de peso en esa población.

Resumo:
OBJETIVO: Verificar a concordância entre os critérios de avaliação de IMC (Índice de massa corporal) propostos pelo Centro de Controle e Prevenção de Doenças (CDC) e pela Força Tarefa Internacional de Obesidade (IOTF) em adolescentes escolares do município de Petrolina - PE.
MÉTODOS: Participaram 1169 escolares, sendo 660 do sexo feminino e 509 do sexo masculino com idades entre 12 e 17 anos. Foram aferidas massa corporal e estatura, e o IMC foi calculado de acordo aos parâmetros do CDC e IOTF. Duas formas de análise foram adotadas, sendo uma utilizando quatro grupos de classificação (baixo peso, eutrofia, sobrepeso e obesidade) e outra empregando dois grupos (com e sem excesso de peso). A concordância entre os parâmetros foi avaliada por meio do índice Kappa.
RESULTADOS: A prevalência de excesso de peso foi de 15,3% de acordo com o CDC e 15,9% de acordo com o IOTF. O índice Kappa variou de bom (k=0,75) para quatro grupos a muito bom (k=0,92) para dois grupos.
CONCLUSÃO: O IMC na amostra foi similar entre os parâmetros aplicados e os mesmos apresentaram elevada concordância, principalmente quando o objetivo é detecção de excesso de peso nessa população.

INTRODUCTION

The Body Mass Index (BMI), widely used in adults, has been increasingly used to describe and classify the nutritional status of children and adolescents1. It is an instrument that provides a good correlation with the amount of body fat in epidemiological studies2,3. However, in order to provide a consistent assessment of overweight and obesity in children and adolescents, the BMI of these individuals should be assessed using age-related reference curves2 or cut-off points that should be in agreement with values used in adults4.

Therefore, the International Obesity Task Force (IOTF)5,6, proposed cut-off points based on the population of six countries, including Brazil, which are specific by sex and age, ranging from two to 18 years. These cutoff points correspond to those employed in adults, which considers BMI of 18.5 kg / m2 for detection of low weight, 25 kg / m2 indicating overweight and 30 kg / m2 indicating obesity.

In order to evaluate BMI in children and adolescents, the percentile growth curves updated by the Centers for Disease Control and Prevention (CDC) were created. These provide BMI percentiles for children and adolescents over two years of age, divided by sex, obtained from the National Health Surveys of the United States of America7. However, although both the IOTF and CDC criteria are commonly used in the diagnosis of overweight and obesity among children and adolescents 8 , studies find a diversified agreement to detect these variables in both references9,10.

Thus, the objective of this study was to verify the agreement between the criteria of BMI assessment proposed by the CDC and the IOTF in school adolescents in the city of Petrolina - PE.


METHODS

This is a school-based epidemiological study, and a descriptive character with a cross-sectional design. Adolescents of both sexes with ages between 12 and 17 years old, who were duly enrolled in the state educational institutions located in the urban area of the Petrolina city were included. We excluded adolescents who did not agree to gauge body mass and height.

Prior to the start of the collection, a pilot study was conducted to identify possible limitations in the research procedures and to carry out the training of the 10 researchers involved in the study. Data were collected at a state public school with 80 adolescents. Data collection was carried out at primary and secondary schools of the public (state) network, located in the city of Petrolina - PE, from March to July 2014. The distribution of the sample was made by the size of the schools and the enrollment period of students (daytime), in order to guarantee sample proportionality. Schools were classified into three categories: small (less than 200 students); (200 to 499 students); and large (500 students or more). Students enrolled in the mornings and afternoons were grouped into a single category (daytime students)11.

All 29 urban schools in the state public network were considered eligible for inclusion in the study. The randomization of schools was performed in the WinPepi program. Nine selected elementary and middle schools were considered, which represented 31.03% of the schools.

To quantify the sample, the WinPepi program was used , in which a population of 25,635 students was considered, a 95% confidence interval; maximum tolerable error of five percentage points; sample loss of 20%; and prevalence of overweight of 13.9%11, generating the quantitative sample of 229 adolescents. The sample size was multiplied by 2.0 (effect of the sampling design), totalizing 458 adolescents. However, as a result of this study being part of a larger project that included other risk behaviors and considering the evaluation of a minimum number of 17 students per class, 1169 adolescents were assessed, of which 660 were female and 509 were male.

The study was approved by the Research Ethics Committee of the University of Pernambuco under protocol CEP / UPE nº 24288213.2.0000.5207. The research obeyed the precepts of Resolution 466/12 of the National Health Council (CNS), and the guidelines of the Statute of the Child and Adolescent. The participants of the study were clarified regarding the objectives and methodologies proposed by means of the Informed Consent Term and the Term of Assent. At least one parent or legal representative signed the first document, and the teen signed the second, thus agreeing to the completion of the research.


Procedures

The volunteer teens were organized in the classroom and invited to participate in the research. The anthropometric data were then checked. The anthropometric evaluation consisted of the measurement of body mass and height, respectively, using a portable digital scale with an accuracy of 0.1 kg and a maximum capacity of 150 kg (CAMRY) and portable stadiometer, with a precision of 0.1 cm and maximum extension of 2.20 meters (WCS). To perform the gauging procedure, the adolescents stood erect, barefoot, arms outstretched at the side of the body, heels joined and the toes apart, in deep inspiration.

The anthropometric data obtained were used to calculate BMI, expressed in body mass in kilos divided by the square of height in meters (kg/m2). The classification of BMI by percentiles for age and for sex was obtained through the growth curves of the CDC and the cut points proposed by the IOTF. For the classification of the BMI by means of the IOTF, the cut-off points for low weight, overweight and obesity at different ages and sex5.6.

For the classification of BMI by CDC percentiles, adolescents with values lower than the 5th percentile were considered underweight; equal or higher than percentile 5 and lower than percentile 85 were considered eutrophic; equal to or greater than the 85th percentile and less than the 95th percentile were considered overweight; and equal to or greater than the 95th percentile were considered obese12.

For the diagnosis of BMI, two forms of presentation were adopted, one using four classification groups (low weight, eutrophic, overweight and obesity) and another using two groups: being non-overweight (low weight and eutrophic) and excess weight (overweight and obesity).


Data analysis

Data tabulation was performed in the Microsoft Excel program using the double-entry procedure. Data were processed and analyzed using the Statistical Package for the Social Sciences (SPSS), version 20. The descriptive analysis included distribution of absolute and relative frequencies. Chi-square tests were performed to verify the existence of significant differences between the different ages and sexes. The weighted Kappa index was used to evaluate the concordance between the BMI references, being considered as poor ( ≤ 0.20), reasonable (0.20 to 0.40), moderate (0.41 to 0.60), good (0.61 to 0.80) and very good (> 0.80)13. The significance level of the study was set at p <0.05.


RESULTS

The present study found prevalence of overweight in 15.3% according to the CDC and 15.9% according to the IOTF for the school adolescents evaluated. There was no significant difference in BMI results between the different ages or sexes within each parameter (p> 0.05), although the prevalence of excess weight seems to be higher in girls at most ages.

Tables 1 and 2 show the BMI classifications according to the IOTF and CDC scores divided into four groups (low weight, eutrophy, overweight and obesity) and in two groups (with and without excess weight), respectively, according to the sex and age of the adolescents. It can be observed that in the classification by the CDC, higher prevalence of obesity were verified, while higher rates of overweight were found by IOTF.






The agreement values between the two parameters (IOTF and CDC) are presented in table 3. It can be observed that when the four BMI classification groups are compared, the level of agreement between CDC and IOTF, on average, is presented good ( kappa = 0.75). However, when assessing two groups, the average agreement between the two references is very good ( kappa = 0.92).



DISCUSSION

The prevalence of overweight among the evaluated students was quite similar between the two classification criteria used. The results provided by the CDC and IOTF parameters in the present study corroborate with data found in studies developed with adolescents from the State of Pernambuco 14 with a prevalence of 16%.

The concordance between the two references was good when applied to the four BMI classification groups and very good when analyzed with the two classification groups. A previous study with children aged two to seven years found good agreement between the two references analyzed with a kappa index ranging from 0.64 to 0.6915,16.

Our findings corroborate with Flegal et al.17 who analyzed adolescents aged 15 to 17 years and verified higher prevalences of overweight and lower obesity through IOTF when compared to the CDC reference. In a study developed by Janssen et al.18 for IOTF and CDC, respectively, were overweight values of 11.1% and 9.9%, while for obesity, 4.3% and 6.4%, respectively. In children, authors also found a higher prevalence of overweight using the CDC when compared to the IOTF15,16, justifying the fact that the IOTF is a more specific and less sensitive parameter in the identification of obesity in this population when compared to the CDC19.

However, it is worth noting that even though the level of agreement between the two diagnostic criteria examined is good at the time of the evaluation of the four groups, the CDC seems to allow the early identification of a greater number of obese individuals compared to the IOTF16. As a result, the use of the IOTF reference could underestimate obesity in adolescence15.

In summary, the CDC and IOTF references are effective in assessing the state of adiposity in children and adolescents20 and have high specificities (84% to 99% respectively) in the detection of excess weight and metabolic disorders in adulthood18. Therefore, it is important to stimulate the use of growth curves in the evaluation of health professionals in order to prevent overweight and reduce the risk of metabolic complications. Conducting weight control early in life using BMI in the clinical context is of great importance for assessing the presence of risk to the health of adolescents. The IOTF and CDC criteria are useful and effective diagnostic tools for assessing the body mass status of this population18.

However, some limitations should be mentioned in relation to the present study, such as the fact that the results are limited to schoolchildren aged 12 to 17 years from a city in the interior of Pernambuco, failing to extend the findings to other age groups or generalize to the rest of the country. In addition, only IOTF cut-off points were used for ages with integers, not including fractional numbers at the time of evaluation as suggested. Future studies are needed to establish a standard and unique criterion for monitoring the nutritional status of adolescents in order to facilitate adequate care for the individual or population.


CONCLUSION

The prevalence of overweight and obesity in the adolescents evaluated varied when compared to the growth curves of the CDC and IOTF, but the agreement between the two parameters was good. However, when adolescents were overweight, the agreement between the two references was very good.


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