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BMI remains ‘good, simple’ diagnostic test for childhood obesity

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October 4, 2016

BMI correctly identifies most children with overweight or obesity and remains the best method to measure adiposity, according to recent findings.

“Perhaps contrary to popular opinion, this review found that BMI is a reasonably good, simple diagnostic test for identifying childhood obesity and adiposity,” Mark Simmonds, PhD, a research fellow at the Centre for Reviews and Dissemination at the University of York, United Kingdom, and colleagues wrote. “It identifies most adipose children correctly, but does fail to identify around 20% of obese or highly adipose children, while misclassifying only a small number as obese.”

In a systematic review, Simmonds and colleagues analyzed data from 25 population-based studies of children undergoing a simple index test to measure adiposity, including BMI (n = 22), skin-fold thickness (n = 7), waist circumference (n = 7), waist-to-hip ratio (n = 3), waist-to-height ratio (n = 2) and relative weight (n = 2). Any included study compared the index test with a reference standard and assessed the sensitivity and specificity of the index tests.

Definitions of overweight or obesity varied across studies; skin-fold thickness was sometimes measured on the triceps, subscapular or a combination of both. Of the references studies, five used densitometry, one used deuterium dilution and the rest used DXA.

Researchers found that BMI correctly detected 81.9% of children with obesity vs. reference standards (95% CI, 73-93.8), with a false-positive rate of 4%. BMI detected fewer children with overweight (76.3% sensitivity; 95% CI, 70.2-82.4) at a higher false-positive rate of 7.9%, according to researchers.

Waist circumference correctly detected 83.8% of children with obesity vs. reference standards, with a false-positive rate of 3.5%; the test correctly detected 73.4% of children with overweight, with a false-positive rate of 5.3%.

Skin-fold thickness tests correctly detected 72.5% of children with obesity vs. reference tests, with a false-positive rate of 6.3%, and correctly detected 78% of children with overweight, with a false-positive rate of 9.7%.

Researchers noted that there were too little data to perform meta-analyses on waist-to-height ratios, waist-to-hip ratios and relative weight, adding that there was no conclusive evidence that any simple test should be preferred to BMI.

“In particular, the extra complexity involved in performing skin-fold thickness tests does not appear to result in any great improvement in diagnostic accuracy,” the researchers wrote. “While BMI is a good, simple test for childhood obesity, it is not perfect, and some obese children will not be identified using BMI.” – by Regina Schaffer

Disclosure: The researchers report no relevant financial disclosures.

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