Regional intra-subject variability in abdominal adiposity limits usefulness of computed tomography

Computed tomography (CT) and magnetic resonance imaging, the most accurate methods of abdominal fat measurement, have been applied using a number of protocols, ranging from single-slice area determination to multiple-slice volume calculation. The aim of this study was to assess the validity of single-slice CT for abdominal fat area measurement by estimating the intra-subject variability in abdominal fat areas and comparing the ranking of subjects across four contiguous abdominal levels.

Nineteen premenopausal women (age, 35.3 +/- 1.4 years; mean +/- SE) were studied. CT was used to measure intra-abdominal fat (IAF) area, percentage of total intra-abdominal area (%IAF), subcutaneous abdominal fat (SAF) area, and IAF/SAF at four adjacent cross-sectional lumbar levels (L2-L4). Intra-subject variability (percentage) was defined as SD/mean x 100. Total body fat was measured by DXA, which was further analyzed for central abdominal fat.

Mean body mass index was 24.9 +/- 1.0 kg/m(2). The average (range) intra-subject variability was 28% (8% to 61%) for IAF, 46% (19% to 124%) for %IAF, 26% (14% to 38%) for SAF area, and 19% (7% to 71%) for IAF/SAF. The pattern of this variability was not uniform between subjects, because their ranking by IAF area was markedly different at each CT level.

We demonstrated significant intra-subject variability in CT-measured adipose tissue areas across four predetermined sites. This resulted in a difference in the ordering of subjects by IAF at each of the four imaging sites, suggesting that the usefulness of single-slice CT in the assessment of abdominal adiposity in premenopausal women may be limited, particularly when performed for the purpose of making comparisons between subjects based on abdominal fat area.