Brian Oldroyd

In vivo precision of the GE Lunar iDXA densitometer for the measurement of total body composition and fat distribution in adults.

In vivo precision for body composition measurements using dual energy X-ray absorptiometry (DXA; GE Lunar iDXA, GE Healthcare, Bucks, UK) was evaluated in 52 men and women, aged 34.8 (s.d. 8.4; range 20.1–50.5) years, body mass index (25.8 kg/m2; range 16.7–42.7 kg/m2). Two consecutive total body scans (with re-positioning) were conducted. Precision was excellent for all measurements, particularly for total body bone mineral content and lean tissue mass (root mean square 0.015 and 0.244 kg; coefficients of variation (CV) 0.6 and 0.5%, respectively). Precision error was CV 0.82% for total fat mass and 0.86% for percentage fat. Precision was better for gynoid (root mean square 0.397 kg; CV 0.96%) than for android fat distribution (root mean square 0.780 kg, CV 2.32%). There was good agreement between consecutive measurements for all measurements (slope (s.e.) 0.993–1.002; all R2=0.99). The Lunar iDXA provided excellent precision for total body composition measurements. Research into the effect of body size on the precision of DXA body fat distribution measurements is required.

Vitamin k status among children with cystic fibrosis and its relationship to bone mineral density and bone turnover

Objective. The aim of this study was to assess vitamin K status in an unselected population of children with cystic fibrosis (CF) and to investigate any vitamin K effect on bone turnover and bone mineral status. Methods. Children ≥5 years of age who were attending the CF unit were invited to enter the study. Fasting blood samples were analyzed for levels of vitamin K1 and prothrombin produced in vitamin K absence; total, undercarboxylated, and carboxylated osteocalcin (OC); and bone-specific alkaline phosphatase and procollagen I carboxy-terminal propeptide (bone formation markers). Levels of N-telopeptide and free pyridinoline and deoxypyridinoline (bone breakdown products) were measured in urine samples. Bone mineral density and bone mineral content were measured at the lumbar spine and for the total body with a GE Lunar Prodigy densitometer. Statistical analyses were performed with Minitab version 9.1. Results. One hundred six children entered the study. Sixty-five of 93 children (70%) from whom blood samples were obtained showed suboptimal vitamin K status, on the basis of low serum vitamin K1 levels, increased prothrombin produced in vitamin K absence levels, or both abnormalities. Vitamin K1 levels showed a significant negative correlation with undercarboxylated OC levels but showed no significant correlation with any marker of bone turnover or measurement of bone mineral status. Undercarboxylated OC levels were correlated significantly with bone turnover markers, which themselves showed a significant negative correlation with measurements of bone mineral density and content. There were no significant correlations between carboxylated or undercarboxylated OC levels and bone density measurements. Conclusions. Vitamin K1 deficiency is common among children with CF, and routine supplements should be considered. Through its role in the carboxylation of OC, vitamin K deficiency may be associated with an uncoupling of the balance between bone resorption and bone formation. A cause-effect relationship between vitamin K deficiency and low bone mass has not been proved.

Comparison of measures of body composition in a trial of low dose growth hormone replacement therapy

OBJECTIVE We assessed the effects of the administration of low dose growth hormone in growth hormone deficient adults on body composition and physical performance. We compared the validity of different measures of body composition in GH treated adults.

Cross-calibration of GE/Lunar pencil and fan-beam dual energy densitometers--bone mineral density and body composition studies.

Objective: In vitro and in vivo comparisons of bone mineral density (BMD) and body composition between GE/Lunar pencil (DPXL) and fan-beam (PRODIGY) absorptiometers.Design: Comparison of BMD, bone mineral content (BMC) and area of lumbar spine (L2–L4), femoral neck and total body. Total body composition compartments tissue (TBTissue), fat (TBF), lean tissue (TBLean) and %TBF were also compared.Setting: Centre for Bone and Body Composition Research, University of Leeds.Phantoms/subjects: A range of spine phantoms, a variable composition phantom (VCP) and total body phantom. A total of 72 subjects were included for the in vivo study.Results: In vitro: A small significant underestimation of BMD by the Prodigy compared to the DPXL ranging from 0.7 to 2% (p<0.05–0.001) for the spine phantoms. The Prodigy underestimated the VCP %Fat. Although the Prodigy underestimated phantom TBBMD by 1.1±1.0%, TBBMC and area were reduced by 8.2±1.4 and 7.3±1.0%, respectively. The Prodigy overestimated TBTissue 1508 g (2.2%), TBLean 588 g (1.2%), TBF 919 g (4.8%) and %TBF (0.8%).In vivo: BMD cross-calibration was only required in the femoral neck, DPXLBMD=0.08+0.906*PRODIGYBMD. The Prodigy had higher estimates for TBTissue 1360 g (2.3%), TBLean 840 g (2.0%), TBF 519 g (3.4%), TBBMC 32.8 g (1.3%) and %TBF (0.3%). Cross-calibration equations were required for TBTissueDPXL=−1158+0.997*TBTissuePRODIGY and TBBMCDPXL= 89.7+0.949*TBBMCPRODIGY.Conclusions: Small differences between the two absorptiometers for both BMD and body composition can be made compatible by use of cross-calibration equations and factors. The discrepancy in body composition compartments requires further research.

Differences in Bone Density, Body Composition, Physical Activity, and Diet Between Child Gymnasts and Untrained Children 7-8 Years of Age†

Strategies that enhance the acquisition of bone mass may be protective against osteoporosis. BMD was compared in 20 artistic gymnasts (10 boys; 10 girls) and 20 untrained children ages 7‐8 years. Higher regional values of BMD were observed in female gymnasts than untrained girls. If retained to adulthood, this higher BMD may protect skeletal integrity in later life.

Annual changes of bone density over 12 years in an amenorrheic athlete.

PURPOSE To link annual changes of bone mineral density (BMD) over 12 consecutive years to pharmacological intervention and to fluctuations of body mass and body composition in an amenorrheic athlete. METHODS BMD of the lumbar spine (LS) and total proximal femur (PF) were measured using dual energy x-ray absorptiometry (DXA), every 11-13 months between ages 24.8 and 36.9 yr. Body composition was assessed every 3-4 yr from a whole body DXA scan. Body mass was recorded every 3 months. For the first 5 yr of study, the subject used oral contraceptives (OC). For the subsequent 7 yr, she used estradiol skin patches (EP) with oral norethisterone. RESULTS The first DXA scan (age 24.8 yr) revealed a low BMD at both LS and PF, with T-scores of -1.4 and -2.8, respectively. During the next 5 yr, while adhering to OC, the BMD of her LS and PF declined by 9.8% and 12.1%, respectively. Concomitantly, her body mass fell from 45.1 to 41.4 kg, her body mass index (BMI) from 16.4 to 15.0 kg.m-2, and her percent body fat from 8.3 to <4.0%. While treated with EP and norethisterone (age 29.8-33.5 yr), her LS BMD gradually increased by 9.4%, despite a further 0.8 kg decline of body mass. From age 33.8 to 36.9 yr, voluntary weight gain (2-3 kg.yr-1; total: 8.1 kg) was accompanied by an increase of her PF BMD (16.9%), with no further increase at the LS. CONCLUSION Changes of BMD at the total proximal femur reflected changes of body mass in this subject. At the lumbar spine, BMD declined with weight loss but increased in association with transdermal estradiol treatment in the absence of weight gain.

In vivo Precision of the GE Lunar iDXA Densitometer for the Measurement of Total-Body, Lumbar Spine, and Femoral Bone Mineral Density in Adults

Knowledge of precision is integral to the monitoring of bone mineral density (BMD) changes using dual-energy X-ray absorptiometry (DXA). We evaluated the precision for bone measurements acquired using a GE Lunar iDXA (GE Healthcare, Waukesha, WI) in self-selected men and women, with mean age of 34.8 yr (standard deviation [SD]: 8.4; range: 20.1-50.5), heterogeneous in terms of body mass index (mean: 25.8 kg/m(2); SD: 5.1; range: 16.7-42.7 kg/m(2)). Two consecutive iDXA scans (with repositioning) of the total body, lumbar spine, and femur were conducted within 1h, for each subject. The coefficient of variation (CV), the root-mean-square (RMS) averages of SDs of repeated measurements, and the corresponding 95% least significant change were calculated. Linear regression analyses were also undertaken. We found a high level of precision for BMD measurements, particularly for scans of the total body, lumbar spine, and total hip (RMS: 0.007, 0.004, and 0.007 g/cm(2); CV: 0.63%, 0.41%, and 0.53%, respectively). Precision error for the femoral neck was higher but still represented good reproducibility (RMS: 0.014 g/cm(2); CV: 1.36%). There were associations between body size and total-body BMD and total-hip BMD SD precisions (r=0.534-0.806, p<0.05) in male subjects. Regression parameters showed good association between consecutive measurements for all body sites (r(2)=0.98-0.99). The Lunar iDXA provided excellent precision for BMD measurements of the total body, lumbar spine, femoral neck, and total hip.

Estimates of percentage body fat in young adolescents: a comparison of dual-energy X-ray absorptiometry and air displacement plethysmography

Objective: To evaluate the accuracy of percentage body fat (%fat) estimates from air displacement plethysmography (ADP) against an increasingly recognised criterion method, dual-energy X-ray absorptiometry (DXA), in young adolescents.Design: Cross-sectional evaluation.Setting: Leeds General Infirmary, Centre for Bone and Body Composition Research, Leeds, UK.Subjects: In all, 28 adolescents (12 males and 16 females), age (mean±s.d.) 14.9±0.5 y, body mass index 21.2±2.9 kg/m2 and body fat (DXA) 24.2±10.2% were assessed.Results: ADP estimates of %fat were highly correlated with those of DXA in both male and female subjects (r=0.84–0.95, all P<0.001; s.e.e.=3.42–3.89%). Mean %fat estimated by ADP using the Siri (1961) equation (ADPSiri) produced a nonsignificant overestimation in males (0.67%), and a nonsignificant underestimation in females (1.26%). Mean %fat estimated by ADP using the Lohman (1986) equations (ADPLoh) produced a nonsignificant underestimation in males (0.90%) and a significant underestimation in females (3.29%; P<0.01). Agreement between ADP and DXA methods was examined using the total error (TE) and methods of Bland and Altman (1986). Males produced a smaller TE (ADPSiri 3.28%; ADPLoh 3.49%) than females (ADPSiri 3.81%; ADPLoh 4.98%). The 95% limits of agreement were relatively similar for all %fat estimates, ranging from ±6.57 to ±7.58%. Residual plot analyses, of the individual differences between ADP and DXA, revealed a significant bias associated with increased %fat (DXA), only in girls (P<0.01).Conclusions: We conclude that ADP, at present, has unacceptably high limits of agreement compared to a criterion DXA measure. The ease of use, suitability for various populations and cost of ADP warrant further investigation of this method to establish biological variables that may influence the validity of body fat estimates.

A cross-sectional study of bone mineral density in children and adolescents attending a Cystic Fibrosis Centre

BACKGROUND Low bone mineral density is common in adults with cystic fibrosis. Children with good lung function compared to controls matched for body size have normal bone mineralisation. There are few data in large unselected populations of children. METHODS All children between five and 16 years were invited to take part. Disease severity was assessed. Bone mineral measurements using a GE-Lunar Prodigy densitometer were expressed as age and gender matched Z-scores. Bone mineral apparent density for L2-L4 was estimated and data from UK Caucasian children used to create age and gender specific reference ranges for predicted values. Z-scores were calculated. Total body analysis utilised the Molgaard method. Blood was sampled for measurement of 25-hydroxyvitamin D, and parathyroid hormone levels. RESULTS 107 children entered the study. 18 and 10 children had low areal and apparent bone mineral density respectively. Short, narrow bones were common. Fifteen children reported 22 fractures, 20 with associated trauma. The best predictors of bone status were ZBMI and percent predicted FEV(1). CONCLUSIONS Bone mineral density corrected for body size was normal in over 90% of children. These results are similar to previously reported results in small studies of children with well preserved respiratory function.

Comparison of changes in bone mineral in idiopathic and secondary osteoporosis following therapy with cyclical disodium etidronate and high dose calcium supplementation

OBJECTIVE Our clinical practice has been to offer treatment with cyclical disodlum etidronate and high dose calcium supplements (1500–1600 mg/day) to ail female patients with osteoporosis who are unable or unwilling to take hormone replacement therapy (HRT), and male osteoporotics. In a retrospective study we compared the effect of this treatment on measures of bone mineral over a 12‐month period in women wlth post‐menopausal and secondary osteoporosis. We also assessed its effects in 10 male osteoporotics.