Comparison of visceral fat measurement by dual-energy X-ray absorptiometry to computed tomography in HIV and non-HIV

Abstract

Background/objectives: Individuals with HIV are susceptible to visceral fat accumulation, which confers an increased risk of cardiometabolic disease. Advanced software to ascertain visceral fat content from dual-energy X-ray absorptiometry (DXA) has not been validated among this population. We sought to compare DXA with computed tomography (CT) in the measurement of visceral fat cross-sectional area (VAT) in HIV and non-HIV using Bland-Altman analyses.

Subjects/methods: Data were combined from five previously conducted studies of individuals with HIV (n = 313) and controls without HIV (n = 144) in which paired DXA and CT scans were available. In cross-sectional analyses, DXA-VAT was compared with CT-VAT among participants with and without HIV. In longitudinal analyses, changes in VAT over time were compared between DXA and CT among participants with and without HIV receiving no intervention over 12 months and among individuals with HIV receiving tesamorelin-a medication known to reduce VAT-over 6 months.

Results: In HIV, DXA underestimated VAT compared with CT among individuals with increased visceral adiposity. The measurement bias was -9 ± 47 cm2 overall, but became progressively larger with greater VAT (P < 0.0001), e.g., -61 ± 58 cm2 among those with VAT ≥ 200 cm2. Sex-stratified analyses revealed that the relationship between VAT and measurement bias was especially pronounced in men (P < 0.0001). Longitudinally, DXA underestimated changes in VAT, particularly among those at the extremes of VAT gain or loss (P < 0.0001). In contrast to the cross-sectional findings, the tendency for DXA to underestimate longitudinal changes in VAT was evident in both men and women. Analogous findings were seen among controls in cross-sectional and longitudinal analyses.

Conclusions: DXA underestimated VAT relative to CT in men with and without HIV, who had increased visceral adiposity. DXA also underestimated changes in VAT over time in men and women, irrespective of HIV status. DXA-VAT should be used with caution among both HIV and non-HIV-infected populations.

Conflict of interest statement

The authors have no disclosures relevant to the design of this study or the preparation of this manuscript. Unrelated to this work, S.E.L. is a non-paid Board member of the community non-profit organization Healing Our Community Collaborative, and received one-time compensation for CME educational offerings sponsored by the Association of Nursing in AIDS Care (Conference, Atlanta, GA, 2017) and New England AIDS Education and Training Center, (Boston, MA, 2018). J.L. has provided consulting services to Gilead Sciences and Viiv Healthcare. T.L.S. has received investigator-initiated funding from Novo Nordisk and Kowa Pharmaceuticals. S.K.G. has received research funding from Gilead Sciences, Kowa Pharmaceuticals, and Theratechnologies, and served as a consultant for Navidea and Theratechnologies. All other authors declare no competing financial interest.

Figures

Fig. 1. Comparison of DXA and CT for cross-sectional VAT and SAT measurement in HIV.

a In HIV, there is a strong correlation between CT and DXA in the measurement of VAT (r = 0.91, P < 0.0001), although the regression line (shown with 95% confidence bands) deviates from the dotted line of unity (P < 0.05). The Bland–Altman plot for VAT demonstrates that measurement bias (DXA–CT) is progressively more negative with greater visceral fat content (P < 0.0001). Horizontal dotted lines denote the mean difference between DXA and CT, as well as the expected 95% limits of agreement. Measurement bias in individuals with the most severe visceral fat accumulation is not contained within the scope of these lines. b There is a strong correlation between CT and DXA in the measurement of SAT (r = 0.94, P < 0.0001). Unlike VAT, the regression line (shown with 95% confidence bands) does not differ from the dotted line of unity. The Bland–Altman plot for SAT demonstrates that DXA overestimates SAT consistently across the subcutaneous fat spectrum. Horizontal dotted lines denote the mean difference between DXA and CT, as well as the expected 95% limits of agreement

Fig. 2. Sex differences in VAT measurement bias in HIV

Sex-stratified analyses reveal that the inverse relationship between visceral adiposity and measurement bias (DXA–CT) in HIV is predominantly driven by men (P < 0.0001). In the Bland–Altman plot shown, the line for men (blue squares) has a slope of −0.41 (−0.47 to −0.36), whereas the line for women (red circles) has a slope of −0.09 (−0.17 to −0.003). Accordingly, DXA most substantially underestimates VAT among HIV-infected men with visceral fat accumulation. Linear regression lines are shown with 95% confidence bands

Fig. 3. Reciprocal relationship between VAT and SAT measurement bias in HIV

Among HIV-infected individuals, DXA progressively underestimates VAT (red circles) in proportion to visceral fat accumulation (P < 0.0001). Conversely, DXA increasingly overestimates SAT (blue squares) as a function of visceral adiposity (P < 0.0001). Linear regression lines are shown with 95% confidence bands

Fig. 4. Comparison of DXA and CT for longitudinal VAT measurement in HIV.

a In the natural history analysis of individuals with HIV, changes in VAT over 12 months by CT and DXA are well-correlated (r = 0.74, P < 0.0001). However, the regression line (shown with 95% confidence bands) deviates from the dotted line of unity (P < 0.05) such that DXA underestimates a gain or loss of VAT as measured by CT. The Bland–Altman plot comparing changes in VAT over 12 months between DXA and CT is also shown. Measurement bias (DXA–CT) is positive among individuals with VAT loss and negative among individuals with VAT gain (P < 0.0001), which again suggests that VAT gain and loss are both underestimated by DXA. Horizontal dotted lines denote the mean difference between DXA and CT in change in VAT over time and the expected 95% limits of agreement. Measurement bias between DXA and CT does not differ between men (blue squares) and women (red circles). b The tesamorelin analysis similarly shows that DXA underestimates changes in VAT over 6 months relative to CT. The extent of underestimation is comparable between individuals treated with tesamorelin (red circles) or placebo (blue squares)