The purpose of this thesis project was to determine the precision error of dual-energy x-ray absorptiometry (DXA) derived bone mineral density (BMD) at regions of interest (ROI) that are clinically relevant to persons with spinal cord injury (SCI), and secondarily to compare the precision error between a group of persons who are able-bodied and a group of persons with chronic SCI. Over 2 visits, four DXA scans at sites of the distal femur, proximal tibia, and calcaneus were completed in 10 persons who are able-bodied and 10 persons with chronic SCI. Using forearm sub region analysis, we measured the BMD and calculated the precision error for a total of 7 ROI at these sites. Despite a lower BMD at every ROI in the group of persons with chronic SCI compared to the group of persons who are able-bodied (range, 33 – 56%), the relative precision error was similar between groups. However, there was a trend for greater precision error in persons with SCI at a whole bone ROI of the distal femur (RMS-CV of 8.40% vs. 5.63%) and a ROI of the posterior calcaneus body (RMS-CV of 3.52% vs. 1.78%) when compared to persons who are able-bodied. Further, the ROI of the posterior calcaneus body appeared to have a lower precision error in persons who are able-bodied (RMS-CV, 1.78%) than the distal femur and proximal tibia (RMS-CV range 3.26 – 5.63%). The results from this study suggest that the precision error of DXA derived BMD is similar between persons with SCI and persons who are able-bodied, and that the posterior calcaneus body may be a more precise site than the distal femur and proximal tibia.

Dual energy x-ray absorptiometry (DXA) provides accurate measurements of percent body fat (%BF) and lean body mass (LBM), however no reference standards currently exist using DXA-derived data. This study’s purpose was to develop reference data sets for DXA-derived %BF and LBM, and to characterize the agreement of obesity classifications between BMI (≥30 kg/m2) and %BF (≥25% for men and ≥30% for women). 2,761 subjects were scanned from 2003-2013 using either the GE Medical Systems Lunar Prodigy or Lunar iDXA. Normative reference tables displaying mean values and select percentiles were created for %BF and LBM across defined age groups for both genders. Mean %BF and LBM closely reflected data from the National Health and Nutrition Examination Survey across age groups in both genders. Agreements between BMI and %BF were 97% when identified as obese and 33% when identified as non-obese. Future research should consider creating a national registry for DXA-derived measurements. / School of Physical Education, Sport, and Exercise Science

We quantified confidence intervals (CIs) for T-scores for the lumbar spine and hip and determined the practical effect (impact on diagnosis) of variability around the T-score cutpoint of -2.5. Using precision data from the literature for GE Lunar Prodigy dual-energy X-ray absorptiometry (DXA) systems, the 95% CI for the T-score was ±0.23 at the lumbar spine (L1-L4), ± 0.20 at the total hip, and ±0.41 at the femoral neck. Thus, T-score variations of ±0.23 or less at the spine, ±0.20 at the total hip, and ±0.41 at the femoral neck are not statistically significant. When diagnosing osteoporosis, T-scores in the interval -2.3 to -2.7 for spine or total hip (after rounding to conform to guidelines from the International Society for Clinical Densitometry) and -2.1 to -2.9 for femoral neck are not statistically different from -2.5. Better precision values resulted in smaller 95% CIs. This concept was applied to actual clinical data using Hologic DXA systems. The study cohort comprised 2388 white women with either normal or osteopenic spines in whom the densitometric diagnosis of osteoporosis would be determined by hip T-scores. When evaluating actual patient T-scores in the range -2.5 ± 95% CI, we found that the diagnosis was indeterminate in approximately 12% of women when T-scores for femoral neck were used and in 4% of women when T-scores for total hip were used, with uncertainty as to whether the classification was osteopenia or osteoporosis. We conclude that precision influences the variability around T-scores and that this variability affects the reliability of diagnostic classification.

Introduction: We determined the prevalence of left-right differences in hip bone mineral density (BMD) by dual-energy x-ray absorptiometry (DXA) and the resultant consequence, namely: the frequency at which patients would be classified differently if lumbar spine and only one hip (rather than both hips) were measured. Methods: This was a retrospective DXA scan reanalysis of 3012 white women ≥50 yrs who had scans of both hips using Hologic DXA systems. The difference between left and right hips was considered significant if it exceeded the least significant change (LSC) for any of three hip subregions (total hip, femoral neck, trochanter). The number of women with osteoporosis in both hips, the left hip only, or the right hip only was determined by lowest T-score from total hip, femoral neck, or trochanter. Results: Despite high left-right correlations of subregion BMD, significant left-right differences in BMD were common: the difference exceeded the LSC for 47% of women at total hip, 31% at femoral neck, and 56% at trochanter. Left-right differences in BMD that exceeded the LSC affected the percent agreement of left-right hip classification: for all women irrespective of spine status, there was 77% classification (diagnostic) agreement in hip pairs in which the left-right hip BMD difference exceeded the LSC versus 87% agreement in which LSC was not exceeded (significant difference in proportions, P<0.0001). The greatest risk of different classification would occur in women with normal spines as the diagnosis might be determined by hip T-scores. Using L1-4 lumbar spine T-scores, 1229 women were normal at the spine. Twenty-four (2%) were osteoporotic at both hips. However, 12 women (1%) were osteoporotic only in the left hip (significantly different from zero, P<0.001) and 11 (1%) only in the right hip (P<0.001); of these 23 women, the difference in BMD between the osteoporotic hip and the contralateral hip exceeded the LSC in 16 (70% of those with osteoporosis in only one hip). Using L1-4 lumbar spine T-scores, 1159 women were osteopenic at the spine. Of these, 126 (11%) were osteoporotic at both hips, 54 (5%) only in the left hip (P<0.001), and 42 (4%) only in the right hip (P<0.001); of these 96 women, the difference in BMD between the osteoporotic hip and the contralateral hip exceeded the LSC in 56 (58% of those with osteoporosis in only one hip). Conclusions: A statistically significant number of women with osteoporosis are potentially classified differently when scanning only one hip as a result of the high prevalence of left-right differences in BMD. Although the percentages are low, the total number of women affected may be large. From a public health perspective, the practice of scanning both hips could potentially identify more women with osteoporosis and may help prevent future hip fractures. © 2006 International Osteoporosis Foundation and National Osteoporosis Foundation.

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International Society for Clinical Densitometry (ISCD) rekommenderar att precisionsbestämning av bentäthetsmätning görs på varje klinik för att bedöma reproducerbarheten. Bentäthetsmätning görs för att diagnosticera osteoporos, följa upp behandling och förutsäga frakturrisk. I studien användes Dual energy x-ray absorptiometry (DXA) för att utföra dubbla mätningar på redan inbokade patienter på klinisk fysiologi, Skånes Universitetssjukhus (SUS), Lund. 105 patienter ingick i studien. Mätningarna utfördes på helkropp, totalhöft, lårbenshals och ländrygg. Helkroppsmätningar ingick i en interindividuell studie och de övriga ingick i intraindividuella studier. Reproducerbarheten uttrycktes som minsta signifikanta skillnaden (LSC), root mean square standardavvikelse (RMS SD) och variationskoefficient (%CV). Reproducerbarheten i studien var god med låga värden för LSC och RMS SD. %CV understeg de av ISCD rekommenderade maxvärdena, vilka är 1,8 % för totalhöft, 2,5 % för lårbenshals och 1,9 % för ländrygg. / It is recommended by the International Society for Clinical Densitometry (ISCD) that every clinic performs a precision assessment of bone densitometry to evaluate the reproducibility. Bone densitometry is used for diagnosis of osteoporosis, to monitor response to treatment and to assess patients’ risk of fractures. Dual energy x-ray absorptiometry (DXA) was used to perform double scans of patients already booked for examination at the section of clinical physiology, Skåne University Hospital (SUS), Lund. 105 patients were included in the study. Measurements were made at whole body, total hip, femoral neck and lumbar spine. The whole body scans were included in an interindividual study, whereas the others were included in intraindividual studies. The reproducibility was expressed as least significant change (LSC), root mean square standard deviation (RMS SD) and coefficient of variation (%CV). The reproducibility in the study was good, with low values for LSC and RMS SD. %CV fell below the maximal values recommended by the ISCD, which are 1,8 % for total hip, 2,5 % for femoral neck and 1,9 % for lumbar spine.

Selective Serotonin Reuptake Inhibitors and Bone mineral Density in a Population of U.S. Premenopausal Women May 2011 M.S., UNIVERSITY of Massachusetts Amherst Directed by: Professor Elizabeth R. Bertone-Johnson Low bone mineral density (BMD) in post-menopausal women is a risk factor for bone fractures and osteoporosis development. Prior studies in post-menopausal women have shown the use of antidepressant medications, specifically selective serotonin reuptake inhibitors (SSRIs) to be inversely related to BMD. However, the association has not been studied in pre-menopausal women. Current SSRI use is widespread with 8% of U.S. women age 18-44 reporting use. We evaluated the association between SSRIs and BMD and bone mineral content (BMC) cross-sectionally using data from the University of Massachusetts Vitamin D Status Study. SSRI use, diet, and lifestyle factors were assessed by questionnaire. BMD and BMC were measured using dual-energy x-ray absorptiometry (DEXA). The study included 256 women aged 18-30 (mean=21.6 years, SD=4.3 years). In this population, SSRI use was 5%, BMD values ranged from 0.97-1.38 g/cm2 (mean 1.16, SD 0.08), and BMC values ranged from 1833g to 3682g (mean 2541.5, SD=349.2). After adjustment for age, body mass index, and physical activity, mean BMD in the 13 users of SSRIs was 1.15g/cm2 (SD=0.06) compared to 1.16g/cm2 (SD=0.77) in the 243 non-users (p =0.66). After the same adjustments, mean BMC in the 13 users was 2467.1g (SD=285.0) compared to 2547.6g (SD=352.6) in the 243 non-users (p=0.94). Our findings do not support an inverse association between SSRI use and BMD or BMC. However, given the prevalence of SSRI use in young women and the potential for adverse effects on bone health, further study of this association is warranted.

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Övervikt och fetma hos barn och ungdomar har blivit allt mer förekommande och prevalensen ökar dramatiskt över hela världen. Sedan raffinerade kolhydrater introducerades har även kariessjukdomen fått större utbredning. Då det finns gemensamma bakomliggande faktorer som påverkar både vikt och kariesprevalens vill vi i vår litteraturstudie undersöka om det finns något samband mellan body mass index (BMI) och kariesprevalens för barn och ungdomar. Efter sökningar i den medicinska databasen PubMed på artiklar från de senaste 5 åren fann vi oeniga resultat med jämn fördelning. Resultatet av litteraturstudien är att två av de undersökta studierna tyder på att det inte finns något samband mellan BMI och kariesprevalens, lika många anser att det finns en svag eller möjlig association, medan två studier ansåg att det fanns ett signifikant samband. Majoriteten av de undersökta studierna kan alltså inte se något signifikant samband mellan BMI och kariesprevalens. För att säkerställa ett samband eller ej krävs fler studier och en djupare analys av tillförlitligheten i respektive studie.