Dual energy X-ray absorptiometry

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)... 

Frediani B, Falsetti P, Baldi F, Acciai C, Filippou G, Marcolongo R. Effects of 4-year treatment with once-weekly clodronate on prevention of corticosteroid-induced bone loss and fractures in patients with arthritis evaluation with dual-energy X-ray absorptiometry and quantitative ultrasound. Bone 2003 33 575-81. 

In a small cross-sectional study, bone mineral density was studied in 20 prepubertal asthmatic patients treated with moderate to high doses of inhaled glucocorticoids (under 400 micrograms/day beclomethasone or budesonide or over 200 micrograms/day fluticasone) (114). Volumetric trabecular bone mineral density of the lumbar spine and distal radius were measured using dual energy X-ray absorptiometry and were within the reference ranges. 

Two imaging systems, dual energy X-ray absorptiometry scanning (DEXA) and magnetic resonance imaging (MRI), allow for longitudinal studies of whole body composition. DEXA measures bone mineral density and content, fat content, and lean content in anesthetized mice. Echo MRI from Echo Medical System, Houston, TX, is used to measure whole body composition parameters such as total body fat, lean mass, body fluids, and total body water in live mice without the need for anesthesia or sedation (15). The MRI technology is more rapid, less than a minute to scan one mouse, than DEXA which takes about 5 min per mouse. 

Several methods are available to evaluate a patient s actual body composition rather than total body mass. Skin-fold measurement may be of value in evaluating subcutaneous adiposity (adipose tissue accumulation) proper technique is required for reliable results. Other anthropomorphic measurements such as bioelectrical impedance, dual-energy x-ray absorptiometry, and total body water immersion are also available.These last techniques are often of value in research studies, but it is clinically impractical to use them routinely (Elberg et al., 2004). 

Bone mineral density (BMD) is measured using dual energy X-ray absorptiometry (DEXA) usually at the neck of femur (on the hip). The World Health Organization defines a diagnosis of osteoporosis if the BMD is 2.5 standard deviations or more below the young adult female mean value. This difference is known as the T-score. Patients are considered to have osteopenia if the T-score is between -1 and -2.5. 

Patients can undergo a dual-energy X-ray absorptiometry (DEXA) scan to confirm the diagnosis of osteoporosis. Osteoporosis is defined as having a bone mineral density which is at least 2.5 standard deviations below the peak bone mass when measured by a DEXA scan (e.g. a T-score -2.5 SD or below). 

In women aged 75 years and older, treatment is recommended without the need for prior dual energy X-ray absorptiometry (DXA) scanning. Bisphosphonates, strontium ranelate, and raloxifene are all suitable for initiation in primary care. However both SIGN (2003) and NICE (2008) recommend that a bisphosphonate (alendronate, etidronate, risedronate, ibandronate) should be used first-line. 

A bone mineral density (BMD) test measures the density of minerals (such as calcium) using X-ray, computed tomography (CT) or ultrasound. Dual-energy X-ray absorptiometry (DEXA) is the most accurate way to measure BMD. DEXA can measure as little as 2% of bone loss per year it is fast, uses low doses of radiation, but is more expensive than ultrasound. 

Effective dose was a parameter used to assess biological risk related to radiation exposure, from dual-energy X-ray absorptiometry (DXA). Children are a worst case estimate because they absorb higher doses than adults. With the exception of the hip scans in 1- and 5-year-old children, the effective doses were below the negligible individual dose limit of 1 mrem per year (Thomas et al, 2005). 

Thomas, S.R., Kalkwarf, H.J., Buckley, D.D., Heuhi, J.E. (2005). Effective dose of dual-energy X-ray absorptiometry scans in children as a function of age. J. Clin. Densitom. 8 415-22. 

Lukashi, H. C. (1993). Soft tissue composition and bone minera status Evaluation by dual-energy X-ray absorptiometry. /. Nufr. 123,438-443. 

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