A comparison of dual‐energy X‐ray absorptiometry, air displacement plethysmography and A‐mode ultrasound to assess body composition in college‐age adults

Summary Background There is currently a dearth of scientific literature exploring the agreement of A‐mode ultrasound (US) body composition analysis with dual‐energy X‐ray absorptiometry (DXA) and air displacement plethysmography (ADP). Objective: To investigate the agreement of US with DXA and ADP for estimating fat mass (FM) and fat‐free mass (FFM). Methods College‐age men (n = 33) and women (n = 41) volunteered to participate in this study. Participants were instructed to adhere to the following pretest protocol: refrain from food and drink 12 h prior to testing and wear tight fitting clothing. Body composition (BCA) was assessed using US, DXA and ADP in accordance with the respective manufacturer's guidelines. Two‐way mixed‐model AVOVA and Bland and Altman techniques were applied to explore agreement for FM and FFM among the three methods: US, ADP and DXA and by sex. Results There was no statistically significant effect by sex for either FM or FFM across all BCA comparisons (P = 0·504 and 0·510, respectively). US was not statistically different from ADP for FM and FFM (P ≈ 1·00). However, for FM and FFM, there were significant differences between DXA and both US and ADP (P≤0·001). The Bland and Altman analyses revealed large individual differences for all BCA. Conclusion There was statistical agreement between US and ADP for FM and FFM but lack of agreement for US and ADP when compared to DXA. However, the large limits of agreement between methods warrant caution in generalizing these findings.