Validation of dual energy X-ray absorptiometry measures of abdominal fat by comparison with magnetic resonance imaging in an Indian population.

OBJECTIVE: Abdominal adiposity is an important risk factor for diabetes and cardiovascular disease in Indians. Dual energy X-ray absorptiometry (DXA) can be used to determine abdominal fat depots, being more accessible and less costly than gold standard measures such as magnetic resonance imaging (MRI). DXA has not been fully validated for use in South Asians. Here, we determined the accuracy of DXA for measurement of abdominal fat in an Indian population by comparison with MRI. DESIGN: 146 males and females (age range 18-74, BMI range 15-46 kg/m(2)) from Hyderabad, India underwent whole body DXA scans on a Hologic Discovery A scanner, from which fat mass in two abdominal regions was calculated, from the L1 to L4 vertebrae (L1L4) and from the L2 to L4 vertebrae (L2L4). Abdominal MRI scans (axial T1-weighted spin echo images) were taken, from which adipose tissue volumes were calculated for the same regions. RESULTS: Intra-class correlation coefficients between DXA and MRI measures of abdominal fat were high (0.98 for both regions). Although at the level of the individual, differences between DXA and MRI could be large (95% of DXA measures were between 0.8 and 1.4 times MRI measures), at the sample level, DXA only slightly overestimated MRI measures of abdominal fat mass (mean difference in L1L4 region: 2% (95% CI:0%, 5%), mean difference in L2L4 region:4% (95% CI: 1%, 7%)). There was evidence of a proportional bias in the association between DXA and MRI (correlation between difference and mean -0.3), with overestimation by DXA greater in individuals with less abdominal fat (mean bias in leaner half of sample was 6% for L1L4 (95%CI: 2, 11%) and 7% for L2L4 (95% CI:3,12%). CONCLUSIONS: DXA measures of abdominal fat are suitable for use in Indian populations and provide a good indication of abdominal adiposity at the population level

US pediatric population-level associations of DXA-measured percentage of body fat with four BMI metrics with cutoffs

Four body mass index (BMI) metrics--BMI, BMI z-score, BMI percentile and BMI%--are commonly used as proxy measures for children's adiposity. We sought to determine a BMI metric that is most strongly associated with measured percentage of body fat (%BF) in the US pediatric population stratified by sex, age and race/ethnicity, and to determine cutoffs that maximize the association for each BMI metric. SUBJECTS, DESIGN AND METHODS: %BF was measured by dual-energy X-ray absorptiometry among N=6120 US boys and girls aged 8.0-17.9 years old from the National Health and Nutrition Examination Survey 1999-2004. We fit piecewise linear regression models with cutoffs to %BF data using each BMI metric as the predictor stratified by sex, race/ethnicity and age. The slopes were modeled differently before and after the cutoffs which were determined on the basis of grid searches

Basal levels of 17-hydroxyprogesterone can distinguish children with isolated precocious pubarche

Background: Basal levels of androgens, in particular 17-hydroxyprogesterone (17OHP), are widely debated as predictors of non-classical congenital adrenal hyperplasia (NCCAH) among patients with precocious pubarche (PP). Many authors have recommended the use of adrenocorticotropic hormone (ACTH) stimulation test in children with PP. The aim of our study was to identify clinical and biochemical predictors of NCCAH in children with PP. Methods: We conducted a prospective study of 92 patients with PP undergoing an ACTH stimulation test. We tested the association of basal clinical and biochemical parameters with NCCAH diagnosis. Patients were suspected to have NCCAH if their stimulated 17OHP plasma levels were >10 ng/mL. In these patients, the diagnosis was confirmed by genetic test. Results: Seven (7.6%) patients resulted having NCCAH. The best basal biochemical predictor for NCCAH was 17OHP level >2 ng/mL. In fact, a basal 17OHP level >2 ng/mL had 100% (95% confidence interval (CI), 59.04–100) sensitivity and 93% (95% CI, 85.3–97.37) specificity. The area under the receiver-operating characteristic curve for 17OHP was 0.99 (95% CI, 0.98–1.007). Conclusions: Basal 17OHP cut-off of 2 ng/mL was very effective in predicting NCCAH among our patients with PP. Assay-specific cut-off would probably be the best strategy to avoid unnecessary ACTH test