Dual x-ray absorptiometry

One of the main determinants of the number of subjects required to reach the desired statistical power is the precision of the measurement tool utilized. More precise measurements will reduce the number of subjects required. As an example, if a study is being conducted to assess the influence of a dietary supplement on body fat, several measurement tools could be used to assess this outcome. These tools range from low levels of cost and precision (e.g. skinfold measurements) to moderate levels (e.g. bioelectrical impedance) to high levels of cost and precision (dual x-ray absorptiometry - DXA). A study that uses skinfold measurements to measure the outcome will require many more subjects than one which employs DXA. Therefore, it is often less expensive in total to utilize a more expensive measurement tool, because the more precise tool will allow the study to have sufficient power with a smaller number of subjects. 

Bone mineral density (BMD) measured using dual x-ray absorptiometry (DEXA) is the current standard method by which to assess BMD in children and adolescents (Loud and Gordon, 2006). It has some limitations in that it only measures bone in two dimensions (g/cm ) and by utilizing the projected area for areal measurements does not account for bone volume or distance of the subject from the beam [i.e., surrounding tissue mass and (re)positioning]. Moreover, the continuous changes in... 

Osteoporosis is a metabolic bone disease characterized by low bone mass and micro-architectural deterioration of bone tissue. This will lead to bone fragility and consequent increase in bone fracture risk. Mean bone mineral density (BMD) is measured with dual X-ray absorptiometry (DEXA) and expressed in Tsc (Tscore). WHO standards are a Tsc that is 1 standard deviation (SD) below mean BMD is graded as normal bone, Tsc between 1 and 1.5 SD below mean BMD is graded as osteopenia and a Tsc of more than 2.5 SD below mean BMD is graded as osteoporosis. When the Tsc is below 1.5 SD mean BMD prevention of osteoporosis must be initiated. Primary osteoporosis is caused mainly by hormone deflciency in both women and men. Secondary osteoporosis may result from endocrine, metabolic, nutritional and autoimmune causes or from immobility because of trauma. Also the use of medicaments such as corticosteroids may be contributing. 

The effects of inhaled glucocorticoids on bone mineral density (measured using dual X-ray absorptiometry of the spine and hip) and biochemical parameters were followed over 18 months. Mean serum osteocalcin concentrations were significantly lower in patients taking beclomethasone dipropionate or budesonide at doses of 800 micro-grams/day and more. However, bone mineral density of the lumbar spine and hip was not affected. The normal advancement of bone mineral density expected in growing children was not affected by inhaled glucocorticoids taken for 7-16 months (SEDA-22,184). 

Bone mineral density (measured by dual X-ray absorptiometry) did not change significantly in asthmatic... 

A correlation between serum concentrations of neuroleptic drugs and prolactin has been claimed (746,747). In 55 patients who had been taking neuroleptic drugs for more than 10 years, higher doses of medication were associated with increased rates of both hyperprolactinemia and bone mineral density loss, as shown by dual X-ray absorptiometry of their lumbar and hip bones (748). 

A 58-year-old schizophrenic woman who had taken haloperidol decanoate 125 mg every 2 weeks had a mildly raised prolactin concentration (505 mIU/1 upper limit of the reference range 450 mlU/hter). Dual X-ray absorptiometry showed osteopenia in her spine and hips. She began taking alendronic acid 5 mg/ day and absorptiometry at 1 year showed that her spine and hip had improved by 7% and 9%, although her prolactin concentrations remained mildly raised. 

Bone mineral density (measured by dual X-ray absorptiometry) did not change significantly in asthmatic children treated for 3-6 years with a mean daily dose of 504 micrograms (189-1322 micrograms) budesonide (85). 

Body composition is a more sensitive indicator of infant nutritional status than measures of size. Depending on the method used, measurements can provide the mass of lean tissue, fat tissue, total body water, and bone. Methods vary greatly in terms of invasiveness, feasibility, cost, technology, need for trained personnel, accuracy, reliability, and precision. The most feasible methods for assessing infant body composition include anthropometry (e.g., skinfold measurements), dual X-ray absorptiometry (DEXA), and isotope dilution. A recent review concluded that for intergroup comparisons, skinfold thicknesses were useful, but for individual infant assessments, DEXA was recommended (Koo, 2000). In the absence of reference data based on a large sample of infants, the interpretation of body... 

Dual X-ray absorptiometry Docosahexaenoic acid Deoxyribonucleic acid Dietary Reference Intakes... 

In a 48-week, open, randomized comparison of continuation of twice-daily zidovudine + lamivudine or replacement with once-daily tenofovir + emtricitabine in 100 individuals taking successful efavirenz-based antiretroviral therapy, limb fat mass was assessed by dual X-ray absorptiometry [70 ]. Fat was preserved or increased in the switch group but fell in the continuation group (mean difference 448 g, 95% Cl = 57, 839). The loss of limb fat was attributed to zidovudine. 

DEXA, dual-energy x-ray absorptiometry ECG, electrocardiogram GH, growth hormone HbAlc, glycosylated hemoglobin Alc. 

Routinely assess acromegaly complications, including blood pressure, glucose tolerance, fasting lipid profile, cardiac evaluations (if clinically indicated), colonoscopy, dual-energy x-ray absorptiometry (DEXA) scan (hypogonadal only), evaluation of residual pituitary function, and evaluation of sleep apnea. 

A standardized approach for diagnosing osteoporosis is recommended using central dual-energy x-ray absorptiometry (DXA) measurements. 

Bone mineral density can be measured at various sites throughout the skeletal system and by various methods. The site of measurement can be either central (hip and/or spine) or peripheral (heel, forearm, or hand). Dual-energy x-ray absorptiometry (DXA) can be used to measure central and peripheral sites of bone mineral density. Quantitative ultrasound, peripheral quantitative computed tomography, radiographic absorptiometry, and single-energy x-ray absorptiometry are used to measure peripheral sites. 

Osteoporosis associated with RA follows a multifaceted pathogenesis, but the primary mechanism likely is mediated by osteoclast activity.12 The cytokines involved in the inflammatory process directly stimulate osteoclast and inhibit osteoblast activity. Additionally, arthritis medications can lead to increased bone loss. Bone mineral density should be evaluated at baseline and routinely using dual-energy x-ray absorptiometry.11,12... 

APV, amprenavir ATV, atazanavir CNS, central nervous system CVD, cardiovascular disease D/C, discontinue ddC, zalcitabine ddl, didanosine DEXA, dual-energy x-ray absorptiometry d4T, stavudine EFV, efavirenz HDL, high-density lipoprotein HIV, human immunodeficiency virus HTN, hypertension IDV, indinavir LDL, low-density lipoprotein LPV/r, lopinavir+ ritonavir MRI, magnetic resonance imaging NNRTI, nonnucleoside reverse transcriptase inhibitor NRTI, nucleoside reverse transcriptase inhibitor NVP, nevirapine PI, protease inhibitor RTV, ritonavir SQV, saquinavir TDF, tenofovir disoproxil fumarate TG, triglyceride TPV/r, tipranivir + ritonavir ZDV, zidovudine. 

Measurement of central (hip and spine) BMD with dual-energy x-ray absorptiometry (DXA) is the gold standard for osteoporosis diagnosis. Measurement at peripheral sites (forearm, heel, and phalanges) with ultrasound or DXA is used only for screening purposes and to determine the need for further testing. 

FIGURE 3-1. Bone health therapeutic algorithm for women. (BMD, bone mineral density CBC, complete blood count DXA, dual-energy x-ray absorptiometry PTH, parathyroid hormone RA, rheumatoid arthritis TSH, thyroid-stimulating hormone.)... 

Beck TJ, Looker AC, Ruff CB, Sievanen H, Wahner HW (2000) Structural trends in the aging femoral neck and proximal shaft analysis of the Third National Health and Nutrition Examination Survey dual-energy X-ray absorptiometry data. J Bone Miner Res 15 2297-2304... 

Sato M, McClintock C, Kim J, et al. (1994) Dual-energy X-ray absorptiometry of Raloxifene effects on the lumbar vertebrae and femora of ovariectomized rats. J Bone Miner Res 9 715-724... 

Dubois EF, Roder E, Dekhuijzen PN, Zwindennan AE, Schweitzer DH. Dual energy X-ray absorptiometry outcomes in male COPD patients after treatment with different glucocorticoid regimens. Chest 2002 121(5) 1456-63. 

Hologic Dexa QDR 4000 used for Dual-energy X-ray absorptiometry (DEXA)... 

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