DEXA is thought to be a more precise measure of body fat than BMI, but no large-scale studies have compared the two as measures of body fat percentage, researchers suggested.
The US team examined BMI and DEXA data from 1,234 patients. In total, 689 were classified as obese using analysis of body fat percentage by DEXA.
However, researchers say that 37 per cent of these patients would not have been classified as obese on the basis of BMI alone.
The researchers conclude that BMI is a not a sensitive measure of obesity and that it under-diagnoses obesity levels in the population.
'The use of BMI should be greatly curtailed, and a direct measure of adiposity should be used on large subgroups of patients often misclassified by this measure,' the researchers said.
Further research would be needed, the researchers argue, to work out how to identify which patients are likely to be mislabelled as obese using BMI measurements and which patients should be assessed using DEXA.