Despite BMI z-scores being widely used in cross-sectional and longitudinal analyses of children with severe obesity, a recent study found that BMI z-score functions poorly as an indicator of adiposity among children with severe obesity.
The researchers used data from the National Health and Nutrition Examination Survey (NHANES) from eight cycles conducted from 1999-2000 through 2013-2014 to describe the relationship of various BMI metrics to other anthropometric indices of obesity among children.
BMI z-scores were calculated by expressing a child’s BMI relative to children in the Centers for Disease Control and Prevention (CDC) growth charts, where obesity is defined as a BMI ≥ 95th percentile.
BMI z-scores based on the growth charts varied by more than threefold across ages. Among children with severe obesity, circumferences and tricep skinfolds showed almost no association with BMI z-score. Based on their analyses, the authors suggested that high BMIs should be expressed relative to the CDC 95th percentile rather than z-scores.