HealthDay News — The US Centers for Disease Control and Prevention has added to the body mass index (BMI)-for-age growth charts, extending them to a BMI of 60 and including additional percentiles. These extended charts have been published in a December 15 report by the CDC National Center for Health Statistics.

Noting that use of BMI-for-age growth charts for children and adolescents with extremely high BMI requires extrapolation beyond the 97th percentile, leading to compression of BMI values into a very narrow range, Craig M. Hales, MD, MPH, from the National Center for Health Statistics in Hyattsville, Maryland, and colleagues examined 8 alternative BMI metrics for monitoring weight status in children and adolescents with extremely high BMI. The metrics evaluated were untransformed BMI, percent of the 95th percentile, BMI units from the median, adjusted BMI units from the median, percent from the median, adjusted percent from the median, modified BMIz, and extended BMIz.

The researchers note that all alternatives provide a solution to the problem of compression at extreme BMI values. The extended method improves BMI distribution characterization at very high values using additional data from the 1999 to 2016 National Health and Nutrition Examination Surveys, rather than relying on extrapolation. In addition, the current CDC 2000 z-scores and percentiles below the 95th percentile are preserved, allowing transitions among weight categories of obesity, overweight, and healthy weight.

“The extended method for calculating z-scores and percentiles stands out among the alternatives,” the authors write.

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