Anthropometric measures: poor predictors of body fat in children with moderate to severe cerebral palsy.

AIM: This purpose of our study was to assess and compare anthropometric measures of adiposity and direct measurement of percentage body fat by dual emission X-ray absorptiometry (DXA) in children with cerebral palsy (CP). We also compared our results in children with CP with results from a national sample of typically developing children from the National Health and Nutrition Examination Survey. METHOD: Anthropometry and DXA were obtained from 58 participants with CP (25 females, 33 males; Gross Motor Function Classification System levels III-V; mean age 13 y 1 mo [SD 3 y], range 8-18 y). Height was estimated from knee height, which was measured with knee height calipers; weight was measured on a sitting scale. The relation between percentage body fat measured by DXA and z-scores of each of the anthropometric measures (body mass index, mid-upper arm circumference, triceps skinfold, and mid-upper arm fat area) was assessed by linear models. Agreement analysis was performed to assess the ability of each anthropometric measure to predict percentage body fat by DXA. RESULTS: None of the anthropometric measures were adequately associated with percentage body fat by DXA. All anthropometric methods tended to underestimate percentage body fat in children with CP. INTERPRETATION: Single anthropometric measures do not perform well in predicting percentage body fat in children with or without CP. Further work is needed to develop clinically useful and simple assessments that will predict percentage body fat and to determine the relation between percentage body fat and health to guide clinical practice.

Assessment and correction of skinfold thickness equations in estimating body fat in children with cerebral palsy.

AIM: To assess the accuracy of skinfold equations in estimating percentage body fat in children with cerebral palsy (CP), compared with assessment of body fat from dual energy X-ray absorptiometry (DXA). METHOD: Data were collected from 71 participants (30 females, 41 males) with CP (Gross Motor Function Classification System [GMFCS] levels I-V) between the ages of 8 and 18 years. Estimated percentage body fat was computed using established (Slaughter) equations based on the triceps and subscapular skinfolds. A linear model was fitted to assess the use of a simple correction to these equations for children with CP. RESULTS: Slaughter's equations consistently underestimated percentage body fat (mean difference compared with DXA percentage body fat -9.6/100 [SD 6.2]; 95% confidence interval [CI] -11.0 to -8.1). New equations were developed in which a correction factor was added to the existing equations based on sex, race, GMFCS level, size, and pubertal status. These corrected equations for children with CP agree better with DXA (mean difference 0.2/100 [SD=4.8]; 95% CI -1.0 to 1.3) than existing equations. INTERPRETATION: A simple correction factor to commonly used equations substantially improves the ability to estimate percentage body fat from two skinfold measures in children with CP.