A method for calculating BMI z-scores and percentiles above the 95th percentile of the CDC growth charts. (17th August 2020)

• Record Type: Journal Article
• Authors: Wei, Rong; Ogden, Cynthia L.; Parsons, Van L.; Freedman, David S.; Hales, Craig M.
• Is Part Of: Annals of human biology. Volume 47:Number 6(2020)
• Page Start: 514
• Page End: 521
• Publication Date: 2020-08-17
• Subjects: Childhood obesity -- body mass index -- growth percentiles -- Half Normal distribution; Human biology -- Periodicals; 612
• DOI: 10.1080/03014460.2020.1808065
• Languages: English
• ISSNs: 0301-4460

Abstract

Abstract: Background: The 2000 CDC growth charts are based on national data collected between 1963 and 1994 and include a set of selected percentiles between the 3 rd and 97 th and LMS parameters that can be used to obtain other percentiles and associated z-scores. Obesity is defined as a sex- and age-specific body mass index (BMI) at or above the 95 th percentile. Extrapolating beyond the 97 th percentile is not recommended and leads to compressed z-score values. Aim: This study attempts to overcome this limitation by constructing a new method for calculating BMI distributions above the 95 th percentile using an extended reference population. Subjects and methods: Data from youth at or above the 95 th percentile of BMI-for-age in national surveys between 1963 and 2016 were modelled as half-normal distributions. Scale parameters for these distributions were estimated at each sex-specific 6-month age-interval, from 24 to 239 months, and then smoothed as a function of age using regression procedures. Results: The modelled distributions above the 95 th percentile can be used to calculate percentiles and non-compressed z-scores for extreme BMI values among youth. Conclusion: This method can be used, in conjunction with the current CDC BMI-for-age growth charts, to track extreme values of BMI among youth.