The health-related risks of obesity such as metabolic syndrome are more common after 10 years of age or at the onset of puberty and likewise recommendations for screening for metabolic syndrome [7-9]. We therefore designed the BMI tool for use from 8 years. The mean value of height, weight and cut-offs for underweight, overweight and obesity were used from the IAP charts [5] to design the tool. Ethics approval for the study was obtained from the institutional ethics committee. The height range for boys and girls for the age group of 8-18 years was plotted on the X-axis. Based on the BMI cut off value for that particular age the corresponding weight to a particular height was calculated and plotted on the secondary Y-axis (Microsoft Excel 2015). Thus, height was plotted on the X-axis, weight on the Y-axis and three lines viz, for underweight, overweight and obesity were constructed on secondary Y-axis. The meeting point of the two lines gives the BMI. Depending on where the BMI point lies, child may be classified as being, obese, overweight, normal weight or underweight. If plotted reading falls below lowest line the child is underweight, if it is between underweight and overweight lines, the child has a BMI within reference range, if the reading falls between overweight and obese lines the child is over-weight, and if above obese line, the child is considered obese. Separate tools were created for both genders.

Sample size was calculated using external prognostic modeling [10] and was recommended to be more than 200. The tool was validated on de-identified data from a health survey [11]. Data were distributed over BMI categories as per the IAP charts into underweight, within reference range, overweight and obese, and used to test sensitivity and specificity of BMI tool. Data on height and weight from validation data set were plotted on BMI tool and simultaneously on the IAP BMI charts. The number of children classified as underweight, within reference range, overweight and obese by the tool and IAP charts was noted. Sensitivity and specificity of the tool against IAP charts was computed (SPSS 25).

Data on 221 (112 boys) children age 8-18 years were used. The gender-wise BMI screening tools are illustrated in Fig. 1 and 2.

Fig. 1 Body mass index screening tool for girls aged 8-18 years.

Fig. 2 Body mass index screening tool for boys aged 8-18 years.

For detection of overweight and obesity in comparison with IAP charts, sensitivity was 95.7% for both boys and girls, whereas specificity was 85.7% for girls and 89.7% for boys. For detection of underweight, sensitivity was 100% for both genders and　specificity was 88.9% for boys and 82.4% for girls.

We have presented a graphic tool based on IAP growth charts in which BMI can be read by plotting height and weight without the need to calculate BMI. The tool demonstrated high sensitivity and specificity for screen-ing children for underweight, overweight and obesity, when tested against IAP BMI charts.

The limitations of the tool are that it is likely to categorize children wrongly at extreme ends of height for age, thus, too tall and very short children may be wrongly classified. The tool cannot be used in children younger than 8 years, and larger studies with a bigger sample size are required for validation and generalization of the tool.

In a study where questionnaires were sent to Ministries of Health of 202 countries, authors found that growth charts were mainly used for children from 0-5 years, and covered birth to adolescence in only 29% [12]. More than half of the countries, including 18 Asian countries, used weight for age charts instead of BMI charts [17]. In a questionnaire-based study to assess usage of growth charts, over two-third of doctors reported a positive attitude towards monitoring of growth; how-ever, perception of high workload was associated with lower usage of growth charts [8]. There are fewer preventive visits to hospitals as children get older [13]. These reports thus underline the importance of devising simple graphic tools to assess nutritional status for use in busy clinical settings.

A similar unisex chart was proposed by Elizabeth, et al. [14] in 2001 based on the International Obesity Task Force cut-offs [15], which may not be appropriate for Indian children at present. Unisex charts may not be appropriate as girls stop growing earlier than boys. The tool designed in the current study may be used in con-junction with IAP charts, and the cut-offs for BMI used are more appropriate for Asian Indian children, who have a higher body fat for a given BMI. However, it is important to remember that this is a quick screening tool and children who are found to be abnormal on the tool or at borderline of categories should be rechecked on the IAP BMI charts after calculating the BMI with standard formula.

To conclude, we present a graphic BMI tool for screening for underweight, overweight and obesity to complement existing IAP charts. The tool is gender specific and is based on height and weight, which eliminates the need for calculation of BMI, and may help pediatricians to rapidly screen for perturbations in BMI in a busy clinical setting.

Ethics clearance: Institutional ethic committee of Jehangir Clinical Development Centre; dated June 21, 2016.

Contributors: VK: concept and design of study, statistical analysis and manuscript draft; NL, SC, AK: data collection, statistical analysis and manuscript draft.

Funding: None; Competing interest: None stated.

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