Comparison of total-body measurements by dual-energy X-ray absorptiometry and dual-photon absorptiometry

Both dual-photon absorptiometry (DPA) using 153Gd and dual-energy x-ray absorptiometry (DEXA) can be used for measurement of bone mineral content (BMC) and bone mineral density (BMD) of the total skeleton and its seven major regions. The short-term precision (coefficient of variation, CV) of DEXA for total-body BMD using the medium (20 minute) and fast (10 minute) speeds was 0.34 and 0.68% in 5 normal subjects; the corresponding CV in 5 osteoporotic females were 0.70 and 1.04%. The CV for BMD using DPA was 0.82% in 8 normal subjects and 0.70% in 12 osteoporotic patients. The CV for regional BMD using DPA was similar to fast-speed DEXA, without significant differences (p NS); precision with medium-speed DEXA was superior to DPA, and the differences were statistically significant (p less than 0.05) for head, spine, trunk, ribs, and pelvis. Total-body measurements using both DPA and DEXA were done on 99 subjects (84 females and 15 males). Significant correlations (r = 0.98; p less than 0.001) were found between DEXA and DPA measurements of both BMC and BMD. There were also significant correlations (r = 0.94-0.98; p less than 0.001) between DEXA and DPA measurements of anatomic regions (head, trunk, spine, pelvis, ribs, arms, and legs). DPA and DEXA results for BMD of total skeleton, ribs, pelvis, and legs were similar (p NS), and statistically significant differences were found in head, spine, and arm measurements (p less than 0.01, p less than 0.01, and p less than 0.05, respectively); regression equations allowed adjustment of DEXA values in patients already measured with the earlier DPA method.     

Sensitivity of dual-photon absorptiometry in spinal osteoporosis

Summary Lumbar spine bone mass and density were measured with Dual photon absorptiometry (DPA) in 60 patients with crush fractures and 60 age-matched normal women. Short-term reproducibility of bone mineral density (BMD) was 1.3% in normal women and 2.5% in osteoporotic women; long-term reproducibility in normal women was 2.2%. The reproducibility of bone mineral content (BMC) seemed to be poorer than that of BMD. In this study, aortic calcifications had no effect on BMD, and one or two crush fractures in the L2–L4 region increased BMD by an average of 3% (0–10%). Lumbar spine DPA provided high sensitivity for these younger crush fracture osteoporotic patients (x=65 years). The sensitivity at 95% specificity was 74% for BMD and 73% for BMC. This sensitivity is substantially better than that reported for DPA instruments giving higher variances or for quantitative computed tomography.     

A population-based comparison of quantitative dual-energy X-ray absorptiometry with dual-photon absorptiometry of the spine and hip

Summary Dual photon absorptiometry (DPA) is currently the most widely used method for noninvasive bone mineral density (BMD) measurement of the axial skeleton. Dual energy X-ray absorptimetry (DEXA) is a recently developed technique that uses an X-ray tube as a photon source; it has demonstrated several significant advantages over DPA in preliminary studies. We report here a quantitative comparison of the DEXA and DPA technologies using a Hologic DEXA (Hologic QDR model 1000, Waltham, MA) scanner and a Lunar DPA (Lunar Radiation DP3, gandolineum-153 source) scanner at both the proximal femur and lumbar spine sites using bone density measurements from a populationbased sample of older white men and women who had complete DEXA and DPA measurements of the hip (n=217) or the spine (n=176). To examine the relationship of BMD measured by the DPA scanner to BMD measured on the DEXA scanner, normal least squares linear regression was used to regress the DPA BMD on the DEXA BMD for each site. DEXA values were consistently lower than DPA values, with an average difference of 16%. The squared multiple correlation (R²) values were at or above 0.95 for almost all sites, with Ward's triangle having the lowest value (0.89). The slope for all sites was similar, ranging from 0.94 to 1.1. Research and clinical centers that wish to change to DEXA technology because of its shorter examination time and greater precision can therefore compare DEXA with DPA values using representative convesion factors.     

Determination of serum 25-hydroxyvitamin D(3) levels in early postmenopausal Iranian women: relationship with bone mineral density.

Serum levels of 25-hydroxyvitamin D(3) (25-OHD(3)) and bone mineral density (BMD) were determined in 73 selected, early postmenopausal women referred to the Bone Densitometry Center, Loghman-Hakim Hospital, Tehran, Iran. The relationship between them was also assessed. 25-OHD(3) levels were measured using high-performance liquid chromatography. BMD was measured with dual-energy X-ray absorptiometry of the lumbar spine and proximal femur regions. 25-OHD(3) levels ranged from 3.8 to 64.0 ng/mL (mean +/- SD: 17.1 +/- 11.3). Twenty-six subjects (36%) were vitamin D-deficient (<12 ng/mL). In the lumbar spine (L2-4) BMD measurements, 28 subjects (38%) were normal (T score > -1), 26 (36%) were osteopenic (T < or = -1 to >-2.5), and 19 (26%) were osteoporotic (T < -2.5). In the hip (total) BMD measurements, 41 subjects (56.1%) were normal, 31 (42.5%) were osteopenic, and 1 (1.4%) was osteoporotic. There was a significant correlation between spine BMD (Z score) and 25-OHD(3) (r = 0.23, p < 0.05), but the correlation was not significant for hip BMD. It was concluded that vitamin D deficiency was evident in early postmenopausal Iranian women, and serum 25-OHD(3) was weakly correlated with spine BMD, which may have physiological significance.     

Precision and stability of dual-energy X-ray absorptiometry measurements

Summary This study was performed to determine the precision and stability of dual-energy X-ray absorptiometry (DEXA) measurements, to compare bone mineral density (BMD) of subjects measured by DEXA and radionuclide dual-photon absorptiometry (DPA), and to evaluate different absorber materials for use with an external standard. Short-term precision (% coefficient of variation, CV) was determined in 6 subjects scanned six times each with repositioning, initially and 9 months later. Mean CV was 1.04% for spine and 2.13% for femoral neck BMD; for whole-body measurements in 5 subjects, mean CV was 0.64% for BMD, 2.2% for fat, and 1.05% for lean body mass. Precision of aluminum phantom measurements made over a 9-month period was 0.89% with the phantom in 15.2 cm, 0.88% in 20.3 cm, and 1.42% in 27.9 cm of water. In 51 subjects, BMD by DEXA and DPA was correlated for the spine (r=0.98,P=0.000) and femoral neck (r=0.91,P=0.000). Spine BMD was 4.5% lower and femoral neck BMD 3.1% higher by DEXA than by DPA. An aluminum phantom was scanned repeatedly, in both water and in an oil/water (30∶70) mixture at thicknesses ranging from 15.2 through 27.9 cm. Phantom BMD was lower at 15.2 cm than at higher thicknesses of both water and oil/water (P=0.05, ANOVA). The phantom was scanned repeatedly in 15.2, 20.3, and 27.9 cm of water over a 9 month period. In 15.2 and 20.3 cm of water, phantom BMD did not vary significantly whereas in 27.9 cm of water (equivalent to a human over 30 cm thick), phantom BMD increased 2.3% (P=0.01) over the 9 months.     

Measurement of bone by dual-photon absorptiometry (DPA) and dual-energy X-ray absorptiometry (DEXA)

Bone densitometry is essential for (a) confirming a diagnosis of osteoporosis, (b) determining the degree of osteopenia and risk of fracture, and (c) monitoring the response of bone to therapeutic agents. Fracture risk at specific axial fracture sites (spine, proximal femur), is associated directly with bone mineral density (BMD) at these sites. ROC analysis demonstrates that the diagnostic sensitivity of spine and femur BMD for spine and/or femur fracture is substantially superior to BMD of appendicular sites in the immediate postmenopausal period. Femoral neck BMD affords high diagnostic sensitivity for proximal femur fracture even in the elderly. Recent prospective studies have shown that bone densitometry can predict future fractures in postmenopausal women. Conventional DPA with 153Gd provides high accuracy for total body, spine, and femur BMD with adequate clinical precision of 1%, 2% and 3%, respectively. Dual-energy x-ray absorptiometry (DEXA), using either switched kVp or by k-edge filtering, offers better precision; typically the precision error is halved. The higher flux available from x-ray sources provides other advantages over DPA, including: improved spatial resolution (2 vs 4 mm), reduced radiation exposure (1 vs 2 mrem), and decreased scan times (3 to 10X). Improved DPA systems, with automatic gain stabilization to minimize drift, could offer clinical precision comparable to DEXA but the scan time and spatial resolution remain as before. Both DPA and DEXA allow detection of therapeutic efficacy in individual patients over the first year or two of therapy.     

Cross calibrated standard values of vertebral bone mineral density in Japanese

The reference value of L2-4 bone mineral density (BMD) was calculated in Japanese population by using cross-calibration formulae among the different types of dual energy X-ray absorptiometry (DEXA) and dual photon absorptiometry (DPA). The scan data of lumbar spine were collected from 16 institutes equipped 3 types of DEXA and 3 types of DPA. After subtraction of inadequate scan data, a total of 1038 cases (376 males and 662 females) were accepted to be a representative “normal” population of Japanese. The L2-4 BMD values were adjusted to one equipment by using cross-calibration equations. There were significant decrease in L2-4 BMD in both sexes at age of seventies or more (9.5% decrease in males and 27.5% in females from the peak bone density).     

Morphometric dual-energy X-ray absorptiometry of the spine: report of a large series and correlation with axial bone mineral density.

We studied vertebral morphometry and its relation to bone mineral density (BMD) in normal Brazilian women (n = 605). All women (age 22-97 years) were ambulatory and healthy. A lateral spine scan was done for morphometric X-ray absorptiometry using an imaging densitometer. In 429 of these women, BMD of the spine and proximal femur also were measured using dual-energy X-ray absorptiometry. All women were white with mean (+/- 1 SD) age of 53.7 (+/- 9.5) years. About 21% of the women over 50 years had a T score for spine BMD lower than -2.5 SD, and 7% had a femoral neck BMD below this osteoporosis threshold. Vertebral heights (anterior, HA; middle, HM; and posterior, HP) and ratios (HA/HP and HM/HP) were assessed. There was no systematic difference between younger (20-49 years) and older (50+ years) women in heights or ratios. The vertebral heights were normalized for those observed in each individual case for the L2-L4 sequence. This normalization was adequate for all vertebral heights; the Z score averaged about +0.1. The average Z score for HA/HP was +0.01, but that for the HM/HP was -0.72, indicating that the latter ratio might differ from the reference population used (white American and European women). We observed a small positive correlation between vertebral heights and spine or femur BMD, but this was due entirely to the influence of body size on BMD. On a group basis, the HM/HP showed a significant association with axial BMD; the 1 SD difference between the lowest and highest quartile was associated with a difference of 8-15% (0.5-1.0 SD) in axial BMD.     

Individual smallest detectable difference in bone mineral density measurements.

Bone mineral density (BMD) measurement is a major outcome measure in osteoporosis. The BMD changes observed must exceed the variability inherent in the measurement process to be considered related to disease progression. The objective of the study was to estimate short-term variability of BMD measurement and to propose a cut-off value for the smallest detectable BMD changes for an individual. To estimate the short-term variability, 70 healthy postmenopausal women aged 53 +/- 4 years (group 1) and 57 elderly osteoporotic postmenopausal women aged 80 +/- 6 years (group 2) had two repeated BMD measurements of the lumbar spine (L2-L4) and the proximal femur with dual-energy X-ray absorptiometry, with complete repositioning within 1 h. Cut-offs derived from short-term variability were either estimated from the coefficient of variation (CV) (which is a function of the measured value) or from the standard deviation (SD), and applied to 330 postmenopausal women (group 3) who had BMD measurements at baseline and 2 years later. The short-term intrasubject variability was greater at the lumbar spine in group 2 versus group 1 (0.0123 vs. 0.0059 g/cm2, p < 10-4), whereas it was not at the femoral neck (0.0098 vs. 0.0076 g/cm2, p = 0.28). There was no statistically significant correlation between short-term intrasubject variability (SD) and BMD as demonstrated with an analysis of covariance (p values ranging from 0.17 to 0.90). Cut-offs estimated with SD and CV were individually applied to group 3 patients. Using these two cut-offs, discrepancies in assessment of progression were observed in 1.7-8.6% of cases. Short-term BMD variability is constant in a wide range of BMD values. Consequently, to determine cut-off values for the smallest detectable differences in BMD at the individual level, precision errors should be based on SD (expressed in absolute units) rather than on CV (expressed in percentage).     

Age-related bone mineral density, bone loss rate, prevalence of osteoporosis, and reference database of women at multiple centers in China.

Our study surveyed age-related bone mineral density (BMD), bone loss rate, and prevalence of osteoporosis in women at multiple research centers in China. Survey results were used to establish a BMD reference database for the diagnosis of osteoporosis in Chinese women nationwide. We used dual-energy X-ray absorptiometry bone densitometers to measure BMD at posteroanterior (PA) lumbar spine (L1-L4; n=8142) and proximal femur (n=7290) in female subjects of age 20-89 yr from Beijing, Shanghai, Guangzhou, Chengdu, Nanjing, and Jiaxing. A cubic regression-fitting model was used to describe the change of BMD with age at various skeletal sites. Peak BMD occurred between 30 and 34 yr of age for femur neck and total femur, and between 40 and 44 yr for spine and trochanter measurement sites. Young adult (YA) BMD values (mean and standard deviation [SD], calculated as the average BMD in the age range of 20-39, were 1.116+/-0.12, 0.927+/-0.12, 0.756+/-0.11, and 0.963+/-0.13 g/cm2 at PA spine, femoral neck, trochanter, and total femur, respectively. The BMD of 85-yr-old women reflected a loss of 32% at the spine and 30-35% at femur measurement sites. The prevalence of osteoporosis, defined as a BMD of 相似文献   

Impact of the analysis of a bone density reference range on determination of the T-score.

There are uncertainties concerning the optimal threshold value of bone mineral density (BMD) for the diagnosis of osteoporosis using dual-energy X-ray absorptiometry (DXA). The most widely accepted clinical criteria are based on T- and Z-scores, derived statistically from an age-dependent BMD reference range that includes healthy young adults. This study has compared different analyses of BMD data of healthy, nonfractured, adult white females aged 18-90 years, consisting of 953 studied with DXA in the L1-L4 spine and 1018 measured at the hip. Four regression curves were applied to each reference data set; mean peak BMD (PBMD(R)) and the age-independent standard deviation (SD(R)) were calculated. These data, plus derived T-score thresholds, were compared with equivalent values (PBMD(YN), SD(YN)) determined from BMDs of a subgroup of young normals. Choice of regression curve caused a variation of 0.044 g/cm(2) in spinal PBMD(R) and 0.015-0.022 g/cm(2) in the hip. The variation in calculated SD(R) between the regressions was minimal (maximum variation, 0.03 SD unit in the spine). A split-linear model was chosen as the best overall fit for both the spine and the hip on the basis of goodness-of-fit and biological plausibility. PBMD(R) and PBMD(YN) varied by less than 1% at the spine or hip. Although the difference between SD(R) and SD(YN) was < or =7% for the hip sites, SD(R) was 0.022 g/cm(2) > SD(YN) for the spine (17% difference). At each hip site, BMD T-score thresholds, derived from regression analysis of the entire reference range (T(R)) or from young normals only (T(YN)), were not significantly different; however, equivalent spinal values differed by 0.062 g/cm(2) for T = -2.5. The percentage of the Australian female population (AFP) aged 50 yr or older and classified as osteoporotic, using population census data and the split-line-based T-score threshold of T(R) = -2.5, was 23% for spinal BMD and 17% for the total hip. For T(YN) = -2.5, the values were 36% (spine) and 17% (total hip). The hip BMDs of this study were greater than those of NHANES III in the third, seventh and eighth decades by as much as 0.6 SD. This produced a difference of 0.049-0.077 g/cm(2) for T(YN) = -2.5 between the two reference ranges.     

Precision of dual-photon absorptiometry

Summary Precision of dual-photon absorptiometry (DPA) measurements was determined in a lumbar spine phantom and in humans. Approximately half of the measurements were made before and half after a¹⁵³gadolinium source change. The phantom was measured with different amounts of acrylic, which simulates human soft tissue, in order to evaluate the influence of body thickness on bone mineral density (BMD). Results of scans analyzed with two software versions from Lunar Radiation Corp., the widely used 08B and a prototype 08C, are compared. DPA with a cold source significantly overestimated BMD in the phantom in the presence of large amounts (more than 25 cm) of soft tissue equivalent with version 08B but not with the newer version 08C. Similiarly, in nine subjects, there was a significant decrease in spine BMD after a source change when scans were analyzed with version 08B (mean difference 0.026 g/cm²,P=0.002) but not with 08C (0.01 g/cm²,P=0.234). No systematic effect of source change on femoral BMD measurements was observed. The SD of the mean difference of two measurements of the nine subjects was 0.019 g/cm² (1.6% of the mean value) for the spine with software version 08B and 0.024 g/cm² (2.0%) with version 08C, 0.03 g/cm² (3.3%) for the femur neck, 0.03 g/cm² (4.0%) for the greater trochanter, and 0.04 g/cm² (4.9%) for Ward's triangle region of the proximal femur. The spine phanton was scanned on two other commercial bone densitometers in order to assess inter-instrument variation. Phantom measurements of L2-4 BMD made on two Lunar Radiation Corp model DP3 scanners which differed by 2% were 10 and 12% higher than those with a Norland Corp. model 2600 scanner.     

Lateral dual-photon absorptiometry: a new technique to measure the bone mineral density at the lumbar spine

Bone mineral density (BMD) measurement of the lumbar spine by dual-photon absorptiometry (DPA) using a radioactive source and more recently an x-ray tube (DEXA) is a useful noninvasive technique to assess bone loss in vertebral osteoporosis. Because an anteroposterior (AP) projection is used, DPA measures not only the mainly trabecular bone of the vertebral body but also the cortical bone of the posterior processes, which does not contribute to the development of crushed fractures. Using a DPA apparatus equipped with a 153 Gd source coupled with an 18-detector system that provides better collection efficiency for the narrow beam of 153 Gd radiation, we have developed a technique measuring the BMD of the vertebral body of L2, L3, and L4 on a lateral projection based on previous studies using radiographic photodensitometry for lateral spine. The precision of the method-1.7% in vivo and 0.88% in vitro-is similar to that obtained with the AP projection (respectively, 1.7 and 1.0%). Lateral BMD decreased with age in 143 normal women and was best accounted for by a cubic curve (r = -0.51, p less than 0.001). The age-related bone loss between 30 and 80 years of age was much higher with the lateral (-44%) than with the AP (-22%) projection, a pattern consistent with the greater trabecular than cortical age-related bone loss. When osteoporotics (OP) were compared to age-matched normal women, the decreased in BMD was larger with the lateral (-30%) than with the AP projection (-23%), but in terms of Z scores, no difference could be found between both projections.(ABSTRACT TRUNCATED AT 250 WORDS)     

Solute-free versus electrolyte-free water clearance in the analysis of osmoregulation

Reduced bone mineral density (BMD) and an increased risk of vertebral fracture have been reported in calcium-stone-forming (CSF) patients presenting with idiopathic hypercalciuria. We investigated the association between BsmI vitamin D receptor (VDR) polymorphism and BMD in 68 hypercalciuric CSF patients (35 males and 33 premenopausal females, mean age +/- SD = 39 +/- 10 years). BMD was measured at lumbar spine (L2-L4) and femur neck sites using dual energy X-ray absorptiometry. A 72-hour dietary record and a 24-hour urine sample were obtained from each patient to determine calcium intake and excretion. The allelic frequency found for the sample as a whole was 16% BB, 44% Bb and 40% bb. Mean BMD values did not significantly differ among BB, Bb and bb patients at L2-L4 (1.162 +/- 0.10, 1.133 +/- 0.11 and 1.194 +/- 0.19 g/cm2, mean +/- SD, respectively) or at neck sites (0.920 +/- 0.11, 0.931 +/- 0.15 and 0.982 +/- 0.15 g/cm2, respectively). Calcium intake and excretion were also not significantly different among the three genotypes. Patients were then divided into two groups, normal BMD, T-score > or =-1 (n = 34) and low BMD, T-score <-1 (n = 34), to further evaluate the allele influence on previous bone loss. Despite a trend for a higher mean BMD at spine or neck sites for patients with one or two b alleles when compared to BB patients, the difference did not reach statistical significance. The distribution of BB, Bb and bb genotypes in the low-bone-mass group (15, 47 and 38%, respectively) was similar to that in the normal-bone-mass group (18, 41 and 14%, respectively). These data suggest that BsmI VDR polymorphism does not play an important role in the bone loss seen in hypercalciuric CSF patients.     

Sequential and precise in vivo measurement of bone mineral density in rats using dual-energy x-ray absorptiometry.

In the design of new strategies for the treatment of osteoporosis, noninvasive, precise, and sensitive bone mass measurement capable of detecting changes over short periods of time in small animals is essential. Most of the models described thus far require the sacrifice of the animals and/or display low reproducibility. Using a dual-energy x-ray absorptiometer (DEXA; Hologic QDR-1000) in an ultrahigh-resolution mode, we measured bone mineral density (BMD) in rats at the levels of lumbar spine (L1-4), proximal tail (caudal vertebrae C2-4), and tibia. Accuracy was evaluated by measuring the mineral content of bone powder capsules (within the range of rat vertebrae BMD), under 0.5-3 cm water to mimic variations in soft tissue thickness. The bone powder capsule mineral content was highly correlated with chemically determined hydroxyapatite content (r = 0.999). In vivo reproducibility was evaluated by calculating the coefficient of variation (CV = 100 x SD/mean) of four to six BMD measurements, each time with repositioning, in seven rats (220-500 g body weight). CV was 1.36 +/- 0.32% (x +/- SD) for lumbar spine, 0.66 +/- 0.50% for proximal tail, and 1.12 +/- 0.45% for tibia. The ability to detect BMD changes was investigated by measuring BMD before and every 4 weeks after ovariectomy (OVX) in 270 g rats, pair fed during the whole experiment. Compared with sham-operated control animals, a highly significant difference in lumbar spine BMD was observed 4 weeks after OVX, which reached a maximum by 8 weeks and remained stable thereafter. At the level of the proximal tibia, the difference was maximal 4 weeks after OVX.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of age and body weight on spine and femur bone mineral density in U.S. white men

Bone mineral density (BMD) was measured in normal white males using 153 Gd dual-photon absorptiometry. Measurements were made on the lumbar spine (n = 315) and on the proximal femur (n = 282) utilizing three regions of interest. There was a small but significant age-related decrease in spinal BMD (r = -0.11; -0.001 g/cm2 per year) and trochanteric BMD (r = 0.27; -0.002 g/cm2 per year). The BMD of the other femoral sites decreased more rapidly; the femoral neck (r = -0.58; -0.005 g/cm2 per year) and Ward's triangle (r = -0.69; -0.007 g/cm2 per year) declined by about 21 and 34%, respectively, from age 20 to age 70. These femoral BMD decreases were three to four times greater than those usually seen in the peripheral skeleton in males but less than the decreases of 25-30 and 40% in the femoral neck and Ward's triangle of white females. This pattern of aging bone loss may partially explain the paucity of spine fractures and the lower incidence of hip fractures in males versus females.     

Dual X-ray and laser absorptiometry of the calcaneus: comparison with quantitative ultrasound and dual-energy X-ray absorptiometry.

The aim of our study was to evaluate the reproducibility and the diagnostic accuracy of a new device for the assessment of bone mineral density (BMD) of the heel, called dual X-ray and laser (DXL Calscan). This technique associates X-ray absorptiometry to the measure of heel thickness with a laser beam. The calcaneus BMD, calcaneus quantitative sonography (QUS), and lumbar spine and total-body BMD, were evaluated in 40 postmenopausal women. On the basis of the BMD T-score measured by dual-energy X-ray absorptiometry (DXA) of L2-L4, 20 women were classified as osteoporotic and 20 women were considered nonosteoporotic according to the WHO classification. The short-term coefficient of variation of the DXL was 2.4% and 1.7% in osteoporotic and nonosteoporotic women, respectively. The calcaneus BMD was lower in osteoporotic than in nonosteoporotic women. Among osteoporotic patients, 14 patients had a T-score lower than -2.5 at Calscan, whereas only 4 patients classified as nonosteoporotic based on the lumbar spine BMD were misclassified by Calscan. In these patients, the sensitivity and specificity of heel ultrasound measurements were 70% and 85%, respectively. The DXL BMD was highly correlated with the total-body BMD, Stiffness at the calcaneus, and the L2-L4 BMD. In conclusion, the new measuring device the Calscan DXL appeared easy to use, the time of examination was relatively short, and the reproducibility was sufficiently good; the diagnostic accuracy and relationships with other devices were good.     

An Investigation of the Diagnostic Value of Bilateral Femoral Neck Bone Mineral Density Measurements

This paper describes a study to assess the clinical value of bilateral femoral neck bone mineral density (BMD) measurements. Although a range of factors will determine clinical decisions, the classification of the site with the lowest T-score is likely to have significant bearing on the management of a patient. While it is common practice to measure BMD at the lumbar spine and a single neck of femur, knowledge of the BMD of the second femur may also be of diagnostic value. Using dual-energy X-ray absorptiometry, BMD of the lumbar spine and right and left femoral neck was measured in a group of 2372 white, Caucasian women (mean age ± SD, 56.6 ±13.9 years) routinely referred for bone densitometry. Analysis of the measurements showed a significant (p= 0.02) but small difference between the mean BMD of the right (0.840 ± 0.152 g/cm²) and left (0.837 ± 0.150 g/cm²) femoral neck. Further investigation of femur scans revealed 79 (3.3%) patients in whom one side was osteoporotic while the other side and spine were normal or osteopenic using the World Health Organization diagnostic criteria in combination with manufacturer”s reference data. Patients in whom the femoral neck BMD measurements differed by less than the precision error of the system were then excluded. This left only 51 (2.2%) patients, that is 29 (1.2%) for right femur and spine scan and 22 (0.9%) for left femur and spine scan, in whom knowledge of both femoral neck BMD measurements could have altered the classification of the lowest site assessed to osteoporotic. These data suggest that there is only a small benefit from performing bilateral femoral neck BMD measurements. Since BMD measurements are only one of a range of factors considered as part of a patient”s management, it is suggested that the extra time, cost and radiation dose associated with measurement of the second femur may not be justified. Received: 28 October 1999 / Accepted: 2 February 2000     

Low bone mineral density in adults with cystic fibrosis

BACKGROUND: Patients with cystic fibrosis have several risk factors for the development of low bone mineral density (BMD). To identify the prevalence and clinical correlates of low BMD in adult patients with cystic fibrosis, densitometry was performed in 151 patients (83 men) aged 15-52 years. METHODS: BMD was measured in the lumbar spine (L1-4) using dual energy x ray absorptiometry (DXA) and quantitative computed tomography (QCT). It was also measured in the proximal femur (total hip and femoral neck) using DXA, and in the distal and ultra distal forearm using single energy x ray absorptiometry (SXA). Biochemical markers of bone turnover, vitamin D levels, parathyroid hormone levels, and a variety of anthropometric variables were also assessed. RESULTS: The mean (SD) BMD Z score was -0.73 (0.85) in the distal forearm, -0.31 (0.92) in the ultra distal forearm, -1.21 (1. 18) in the lumbar spine using DXA, -0.56 (1.36) in the lumbar spine using QCT, -1.25 (1.30) in the femoral neck, and -1.01 (1.14) in the total hip. 34% of patients had a BMD Z score of -2 or less at one or more skeletal sites. Body mass index (0.527, p = 0.01), percentage predicted forced expiratory volume in one second (0.388, p = 0.01), and physical activity (0.249, p = 0.05) were positively related to the mean BMD Z score. Levels of C reactive protein (-0.328, p = 0. 01), parathyroid hormone (-0.311, p = 0.01) and biochemical markers of bone turnover (osteocalcin -0.261 and bone specific alkaline phosphatase -0.249, p = 0.05) were negatively related to the mean BMD Z score. Vitamin D insufficiency (25-hydroxyvitamin D <15 ng/ml) was prevalent (53/139 patients, 38%) despite supplementation with 900 IU vitamin D per day. CONCLUSIONS: Low bone density is prevalent in adult patients with cystic fibrosis. Current levels of vitamin D supplementation appear to be inadequate.     

Corticosteroid effects on proximal femur bone loss

Prolonged high-dose corticosteroid therapy is known to result in an increased risk of osteoporotic fracture. Reductions in bone density have been demonstrated at the distal radius and lumbar spine in patients receiving corticosteroids; however there have been few studies of bone density in the hip (the most important site of osteoporotic fracture) in this context. To examine the effect of corticosteroids on the hip we measured bone mineral density (BMD) by dual-photon absorptiometry at three sites in the proximal femur as well as the lumbar spine in 32 patients aged 18-77 years who had been treated with corticosteroids (mean daily prednisone dose 12.7 mg) for up to 23 years. BMD was compared with the expected values using age regressions in normal subjects. BMD was significantly reduced in the femoral neck, Ward's triangle, and the trochanteric region (p less than 0.001 all sites). In the lumbar spine BMD was also significantly reduced (p less than 0.001). We also measured BMD serially in 29 patients receiving corticosteroids. BMD measurements were made in 12 patients who had already been treated with long-term corticosteroids at the time of first BMD measurement (chronic group) and from the commencement of corticosteroid therapy in 17 patients (acute group). The mean (+/- SEM) change in BMD (g/cm2 per year) in the lumbar spine and femoral neck were 0.006 +/- 0.006 and -0.021 +/- 0.007, respectively, for the chronic group and -0.02 +/- 0.005 and -0.039 +/- 0.006 for the acute group.(ABSTRACT TRUNCATED AT 250 WORDS)