Discrepancies between caliper and portable A-mode ultrasound estimates of subcutaneous fat in older adults

It has been proposed that subcutaneous fat thickness measured by ultrasound corresponds to half of the skinfold thickness measured with calipers at the same anatomical site. This study compared portable A-mode ultrasound and caliper skinfold assessments in older adults. In a cross-sectional sample of 146 participants, fat thickness was measured at the biceps brachii, triceps brachii, subscapular, and suprailiac sites using a BodyMetrix® BX-2000 ultrasound device and a LipoWise PRO digital caliper. Agreement between methods varied markedly by site: Lin's concordance correlation coefficients were 0.21 (triceps), 0.02 (subscapular), and 0.33 (biceps, suprailiac), indicating poor to moderate concordance. The Bradley-Blackwood test showed differences between methods (p < 0.001). Skinfold/ultrasound mean ratios were 1.50 (triceps), 1.20 (biceps), 1.50 (suprailiac), and 2.90 (subscapular). Caliper skinfold measurements consistently overestimate subcutaneous fat thickness versus ultrasound, especially at the subscapular site, limiting interchangeability and potentially compromising clinical assessment accuracy in older adult populations.