Bone Mineral Density Determinations by Dual-Energy x-ray Absorptiometry in the Management of Patients with Marfan Syndrome—Some Factors Which Affect the Measurement

Reduced bone mineral density (BMD) was sporadically reported in patients with Marfan syndrome. This may or may not place the Marfan patient at increased risk for bone fracture. In comparing the BMDs of our patients with those reported in the literature, it seemed that agreement between values, and hence the degree of osteoporosis or osteopenia reported, was dependent on the instrumentation used. The objective of this study was to statistically assess this impression. Bone mineral density measurements from our previously published study of 30 adults with Marfan syndrome performed on a Lunar DPXL machine were compared with studies published between 1993–2000 measured using either Lunar or Hologic bone densitometry instruments. The differences of our measurements compared with those made on other Lunar machines were not statistically significant, but did differ significantly with published results from Hologic machines (P < 0.001). Before progress can be made in the assessment of BMD and fracture risk in Marfan patients and in the evidence-based orthopedic management of these patients, standardization of instrumental bone density determinations will be required along with considerations of height, obesity, age, and sex.     

Accuracy and Precision of 62 Bone Densitometers Using a European Spine Phantom

Dual-energy absorptiometry (DXA) is widely used for bone mineral density measurements. Different types of devices are available. Differences between devices from either the same manufacturer or different manufacturers can lead to difficulties in clinical practice when patients are followed on different machines. We calculated the accuracy and precision of 62 DXA devices from two manufacturers (51 Hologic, 11 Lunar) using a European Spine Phantom (ESP, semi-anthropomorphic). The ESP was measured 5 times on each device without repositioning. Accuracy was assessed by comparing bone mineral density (BMD, g/cm²) values measured on each device with the actual value of the phantom. Precision was assessed by the coefficient of variation (CVsd), using the root mean square average. The limits of agreement were estimated from the differences between each replicate measurement of BMD and the estimated true value for a particular manufacturer, according to Bland and Altman. The results confirm the difference between devices from different manufacturers (18.5%). Mean CVsd values were 0.57% and 0.64% for Hologic and Lunar respectively. The limits of agreement among devices from the same manufacturer were 0.026 g/cm² and 0.025 g/cm² for Hologic and Lunar respectively. Differences in extreme results between devices from the same manufacturer were on average 5.4% and 3.6% for Hologic and Lunar respectively. Results of different devices from the same manufacturer are highly comparable, although unpredictable differences exist that may be clinically relevant. Received: 12 June 1998 / Accepted: 20 November 1998     

The Effect of Extending Femur Scan Length on BMD Results on the Hologic Discovery-W Scanner

A longer dual-energy X-ray absorptiometry scan field of the hip may be useful for the detection of atypical subtrochanteric femur fractures. It has been demonstrated in a Prodigy GE/Lunar scanner that extending the scan length does not affect bone mineral density (BMD) results at the total hip or femoral neck. We hypothesized that extending the scan field on a Hologic Discovery scanner would also have no effect on BMD results at the hip. Thirty subjects who presented for standard of care dual-energy X-ray absorptiometry scans underwent paired default (15.2 cm) and extended (24.1 cm) length hip scans. There was no significant difference in the total hip or any of the component subregions of femoral neck, greater trochanter, or intertrochanteric (shaft) BMD between the default and extended length scans.     

Definition of a population-specific DXA reference standard in Italian women: the Densitometric Italian Normative Study (DINS)

Osteoporosis is currently defined on the basis of the T-score by dual-energy X-ray absorptiometry (DXA). Despite its limitations, this definition is applied worldwide. However, the normal values provided by manufacturers may not be fully representative of specific local populations. So far, there are no normative data in the Italian population using Hologic densitometers. The Densitometric Italian Normative Study (DINS) is an ongoing multi-center study that aims to establish reference values for bone densitometry with dual-energy X-ray absorptiometry (DXA) in the male and female Italian population. In this paper we report the results of the lumbar vertebrae (L2–L4) and proximal femur in 1,622 women aged 20–79 years. Bone mineral density (BMD) was determined using dual-energy X-ray absorptiometry (DXA) on Hologic bone densitometers (Hologic, Waltham, Mass.). Most of the subjects were examined with a QDR 4500. The BMD of the lumbar vertebrae was virtually constant between 20 and 49 years (test for trend: P=0.66); the BMD values between 20–45 in premenopausal women (mean 1.036; SD 0.109 g/cm²) were thus defined as the peak bone mass values, significantly lower compared to the Hologic reference curve (mean 1.079, SD 0.11 g/cm²). The mean BMD values of the femoral neck were virtually identical to those of the NHANES study in the first 3 decades; after the age of 50 the BMD values were slightly greater than those of the NHANES subject. The subject classification according to the WHO criteria was similar using the DINS and NHANES reference values for the femur; for the spine, the Hologic reference values classified a larger proportion of women as osteoporotic (21 vs. 16%) or osteopenic (42 vs. 38%) compared to DINS.     

Cross-calibration of DXA equipment: Upgrading from a hologic QDR 1000/W to a QDR 2000

Summary In this study, the cross-calibration of a fan beam DXA system (Hologic QDR-2000) to a pencil beam scanner from the same manufacturer (Hologic QDR-1000/W) is described. The scanners were calibrated by the manufacturer using the same anthropomorphic spine phantom at installation. To verify consistent machine calibration, a group of 69 female subjects, aged 46–75, had anteroposterior (AP) spine and proximal femur scans on the QDR-1000/W followed by pencil and array scans of the same sites on the QDR-2000 during the same visit. Many of the subjects had bilateral examinations of the proximal femur for a total of 123 hip scans. Pencil and array area, bone mineral content (BMC), and bone mineral density (BMD) from the QDR-2000 were compared with the values obtained on the QDR-1000/W, and linear regression equations were derived for relating the two instruments. At the spine, no differences were found between the QDR-1000/W BMD values and the QDR-2000 array BMD values. A slight difference between pencil beam modes was detected but was not deemed clinically significant. Linear regression models relating the QDR-2000 and QDR-1000/W AP spine BMD measurements showed correlation coefficients greater than 0.99, with slopes of 1.00, intercepts equivalent to zero, and small root mean square errors. Comparisons at the proximal femur showed equivalency at the femoral neck and trochanter regions for the two machines in pencil mode, but slight increases in BMC and BMD at the other femoral sites on the QDR-2000 in both pencil and array mode. Correlation coefficients were 0.97–0.99 for all measurement regions except for Ward's. Regression slopes relating the BMD for the femoral regions were 1.00–1.04, with intercepts not significantly different from zero and small residual errors. As with the spine, the differences were small enough that they were not of clinical significance. However, in longitudinal drug trials requiring highly precise determination of spinal and femoral BMD changes, these differences may be important.     

A multinational study to develop universal standardization of whole-body bone density and composition using GE Healthcare Lunar and Hologic DXA systems

Dual‐energy x‐ray absorptiometry (DXA) is used to assess bone mineral density (BMD) and body composition, but measurements vary among instruments from different manufacturers. We sought to develop cross‐calibration equations for whole‐body bone density and composition derived using GE Healthcare Lunar and Hologic DXA systems. This multinational study recruited 199 adult and pediatric participants from a site in the US (n = 40, ages 6 through 16 years) and one in China (n = 159, ages 5 through 81 years). The mean age of the participants was 44.2 years. Each participant was scanned on both GE Healthcare Lunar and Hologic Discovery or Delphi DXA systems on the same day (US) or within 1 week (China) and all scans were centrally analyzed by a single technologist using GE Healthcare Lunar Encore version 14.0 and Hologic Apex version 3.0. Paired t‐tests were used to test the results differences between the systems. Multiple regression and Deming regressions were used to derive the cross‐conversion equations between the GE Healthcare Lunar and Hologic whole‐body scans. Bone and soft tissue measures were highly correlated between the GE Healthcare Lunar and Hologic and systems, with r ranging from 0.96 percent fat [PFAT] to 0.98 (BMC). Significant differences were found between the two systems, with average absolute differences for PFAT, BMC, and BMD of 1.4%, 176.8 g and 0.013 g/cm², respectively. After cross‐calibration, no significant differences remained between GE Healthcare Lunar measured results and the results converted from Hologic. The equations we derived reduce differences between BMD and body composition as determined by GE Healthcare Lunar and Hologic systems and will facilitate combining study results in clinical or epidemiological studies. © 2012 American Society for Bone and Mineral Research.     

Population Bone Mineral Density Measurements for Chinese Women and Men in Hong Kong

The aim of the study was to establish population ranges of bone mineral density (BMD) for Hong Kong Chinese men and women for the Hologic QDR 2000 bone densitometer, to compare these values with the manufacturer’s reference ranges, to compare these values with population ranges for women obtained for the Norland X26 bone densitometer, and to examine variations between the two densitometers. The subjects were 164 men aged 40–79 years and 436 women aged 20–89 years, who were all ethnic Chinese, recruited from volunteers, social centers for the elderly and general practice clinics. BMD in women began to decline rapidly between ages 50 and 79 years, averaging about 10% loss per decade from the young adult (20–29 years) mean. The percentage losses from young adult mean values in the spine, femroal neck, trochanter and total femur were 23%, 30%, 31% and 33%, respectively, from 20 to 79 years. In the ninth decade no further decrease in BMD occurred with the exception of a further 4% at the hip sites. In men, no decrease in spine BMD occurred between 40 and 70 years. Compared with BMD in the fourth decade, 10%, 13%, and 11% of BMD was lost at the femoral neck, trochanter and total femur, respectively, by the seventh decade. These values show differences compared with the manufacturer’s reference ranges for Caucasians and Japanese. BMD values for the spine were comparable between Hologic and Norland densitometers, but Hologic values for femoral neck and trochanteric regions were lower than the Norland values. Data provided by this study may thus be used as normative values for the Hologic QDR2000 bone densitometer, instead of values provided by the manufacturer. BMD values at the hip sites are not interchangeable between Norland and Hologic bone densitometers, and estimation of numbers of the population with osteoporosis will depend on the model of densitometer used. Received: 31 May 2000 / Accepted: 31 October 2000     

A Comparison of Phantoms for Cross-Calibration of Lumbar Spine DXA

The aim of this project was to compare three phantoms used for cross-calibration of dual-energy X-ray absorptiometers with an in vivo cross-calibration. The phantoms used were the Bona Fide Phantom (BFP), the European Spine Phantom (ESP) and the GE Lunar Aluminum Spine Phantom (ASP). The cross calibration was for L2–L4 lumbar spine bone mineral density (BMD) on a GE Lunar DPX-L and Hologic QDR 2000. The in vivo cross-calibration was obtained using 72 subjects (61 female, 11 male; mean age 49 years, range 14–84 years). The phantoms were measured 10 times without repositioning on both instruments. A further, long-term cross-calibration was obtained with the BFP over a 9 month period. The true linear relationship between the two instruments was calculated used a standardized principal components method. The mean residuals were calculated between each phantom cross-calibration line and the in vivo data to obtain a measure of the goodness of fit between the phantom cross-calibration and the in vivo data. There was no significant difference between the in vitro and in vivo cross-calibrations. The long-term BFP cross-calibration gave an in vitro cross-calibration that is closest to the in vivo cross-calibration in this group of subjects. When calculating Hologic QDR BMD from results on the GE Lunar DPX-L, the ASP underestimates Hologic QDR 2000 BMD by 4% at high BMD and overestimates by 4% at low BMD. The ESP cross-calibration overestimates Hologic QDR2000 BMD by 1% at high BMD and 4% at low BMD. The BFP performs best, overestimating Hologic QDR2000 BMD by between 1.2% and 1.8%, whilst the difference between the long-term BFP cross-calibration and the in vivo data is less than 1% over the range of BMD covered. Received: 19 October 2001 / Accepted: 9 July 2002     

Densitometry of the radius using single and dual energy absorptiometry

Though spinal and femoral measurements are typically preferred for evaluating skeletal density, an abundance of forearm data exists, primarily from single photon absorptiometry (SPA) devices. Most dual X-ray absorptiometry (DXA) scanners are capable of scanning the forearm and provide analysis tools to duplicate conventional SPA measurements. In this study, we have compared the radius density measurements from three commonly available densitometers: a Norland 278 SPA, a Lunar DPX-L, and a Hologic 1000/W. Radius bone mineral density (BMD) on the nondominant forearm was measured in 28 volunteers (21 women and 7 men) aged 24–78, with an average age of 51±17 years. Values were compared and regression relationships derived at corresponding measurement sites. SPA and DXA BMD values were found to be highly correlated (r=0.99) with small standard errors (0.014 g/cm²–0.021 g/cm²), though significant absolute differences were observed at most measurement regions. Correlation slopes ranged from 0.85 to 1.04, with intercepts from 0.01 to 0.08 g/cm². Using the resultant regression equations, SPA BMD values can be converted to DXA values with an expected error of roughly 3%. DXA BMD can also be interconverted between Lunar and Hologic with a similar expected error. In situations where this level of imprecision is acceptable, patient forearm measurements obtained on different systems can be interconverted.     

Bone Mineral Density of the Spine and Femur in Healthy Moroccan Women

Bone mineral density (BMD) measurements using dual-energy X-ray absorptiometry (DXA) are widely used to diagnose osteoporosis and assess its severity. Previous studies show the necessity to establish reference data for bone mass measurements for each particular population. Such data are lacking for the Moroccan population. The aim of this study was to determine spine and femur BMD reference values for the Moroccan female population and to compare them with values from western and other Arab countries. A cross-sectional study of 569 Moroccan women, (randomly selected in the area of Rabat, the capital of Morocco, aged between 20 and 79 yr) was carried out to establish reference values of BMD. Measurements were taken at the lumbar spine and proximal femurs using DXA (Lunar Prodigy Vision, GE). The data were compared with published normative data taken by United States (U.S.), European, Kuwaiti, Lebanese, and Saudi women over 6 decades of age. The percentage of osteoporosis in postmenopausal women using our reference curve was compared to that observed when the other curves (US, European and Arab) implemented in the Lunar machine was used. Our results showed that the Moroccan women showed the expected decline in BMD at both sites with age after peaking at 20–29 years of age. Moroccan females have lower BMD at the spine than U.S., Europeans, and Kuwaitis (approximately 10–12% for patients older than 50 yr). The BMD values of the total femur in Moroccan females were close to western (European and American), and Kuwaitis, but higher than Lebanese and Saudis. Using our reference database, 37.9% of postmenopausal women had spine osteoporosis vs. 39.6% and 23.4% using US/European and Arabic Lunar reference values respectively. At the femurs, 6.7% had osteoporosis vs. 2.5% using the Arabic Lunar reference values. In conclusion, our study emphasizes the importance of using population-specific reference values for BMD measurements to avoid over or underdiagnosis of osteoporosis.     

Low 25-Hydroxyvitamin D and Osteopenia Are Prevalent in Persons ≥55 Yr With Fracture at Any Site: A Prospective, Observational Study of Persons Fracturing in the Community

Bone mineral density (BMD) measurements using dual-energy X-ray absorptiometry (DXA) are widely used to diagnose osteoporosis and assess its severity. Previous studies show the necessity to establish reference data for bone mass measurements for each particular population. Such data are lacking for the Moroccan population. The aim of this study was to determine spine and femur BMD reference values for the Moroccan female population and to compare them with values from western and other Arab countries. A cross-sectional study of 569 Moroccan women, (randomly selected in the area of Rabat, the capital of Morocco, aged between 20 and 79 yr) was carried out to establish reference values of BMD. Measurements were taken at the lumbar spine and proximal femurs using DXA (Lunar Prodigy Vision, GE). The data were compared with published normative data taken by United States (U.S.), European, Kuwaiti, Lebanese, and Saudi women over 6 decades of age. The percentage of osteoporosis in postmenopausal women using our reference curve was compared to that observed when the other curves (US, European and Arab) implemented in the Lunar machine was used. Our results showed that the Moroccan women showed the expected decline in BMD at both sites with age after peaking at 20–29 years of age. Moroccan females have lower BMD at the spine than U.S., Europeans, and Kuwaitis (approximately 10–12% for patients older than 50 yr). The BMD values of the total femur in Moroccan females were close to western (European and American), and Kuwaitis, but higher than Lebanese and Saudis. Using our reference database, 37.9% of postmenopausal women had spine osteoporosis vs. 39.6% and 23.4% using US/European and Arabic Lunar reference values respectively. At the femurs, 6.7% had osteoporosis vs. 2.5% using the Arabic Lunar reference values. In conclusion, our study emphasizes the importance of using population-specific reference values for BMD measurements to avoid over or underdiagnosis of osteoporosis.     

Bilateral comparison of femoral bone density and hip axis length from single and fan beam DXA scans

Dominant/nondominant differences in bone mineral density (BMD) have been observed in the upper extremities. However for the proximal femur, the distinction between dominant and nondominant hips is not clear. The purpose of this study is to evaluate left/right variations in femoral BMD and hip axis length (HAL) in both single beam and fan beam dual x-ray absorptiometry (DXA) scans. A total of 36 women aged 41–76 years (average age 60±10 years) received single beam and fan beam DXA scans of both proximal femora with a Hologic QDR-2000 scanner. Femoral BMD and hip axis length were determined for each scan. Left/right and single beam/fan beam correlations were determined and differences were evaluated using a two-way analysis of variance. Femoral BMD at corresponding measurement regions in opposing femora were highly correlated (r=0.81–0.96). No significant left/right differences were detected. At the femoral neck, the mean BMD difference (± standard deviation) was 1.5%±4.7% in a single beam mode and-0.6%±6.3% in fan beam mode. Though mean values of femoral BMD were equivalent, the observed individual left/right differences were occasionally large (as high as 26% in the femoral neck). The hip axis length of the left and right hips were highly correlated and statistically equivalent. However, hip axis length using fan beam was significantly larger (7.5%) than the single beam measurement with a larger observed variation. We conclude that measurement of a single proximal femur will usually be sufficient for clinical evaluation of BMD and/or hip axis length. However, bilateral BMD measurements are indicated in subjects where unilateral degeneration or disease are suspected. If possible, hip axis length should be measured in single beam mode to avoid magnification errors.     

Femoral and whole-body bone mineral density in middle-aged and older Norwegian men and women: suitability of the reference values

The aim of this study was to compare bone mineral density (BMD) in a population-based sample of middle-aged and older Norwegians, with reference values provided by the manufacturer of the densitometer (Lunar) in order to evaluate whether these reference values are suitable for Norwegians. Additional aims were to estimate the prevalence of osteoporosis. Bone mineral density of the hip and total body was measured by dual-energy X-ray absorptiometry in 2303 men and 3105 women 47–50 and 71–75 years old, respectively, in western Norway, as part of the Hordaland Health Study (HUSK). Of these, 3403 white individuals were free of medications or diseases known to influence bone metabolism (reference group). Compared with the Lunar reference population, men and older women had a slightly but significantly lower BMD of trochanter and total femur and middle aged women had significantly higher total body BMD. Except for the higher mean BMD of total body among middle-aged women and the uniformly lower BMD values of Wards triangle, the deviations from the reference values of the manufacturer were less than 4%. Approximately 2.6% of middle-aged men vs 0.9% of middle-aged women were classified as osteoporotic on the basis of BMD of femoral neck. While the BMD values for femoral neck in this healthy Norwegian population are similar to the reference population of Lunar, the values of trochanter and total femur are lower in all groups except middle-aged women; however, the discrepancies are not of sufficient magnitude to warrant rejection of this commonly used database among Norwegians. Use of the young adult means from the Lunar reference database classified a higher proportion of middle-aged men than women as osteoporotic and osteopenic.     

Discrepancies in normative data between Lunar and Hologic DXA systems

Many studies have shown the high correlation between Lunar and Hologic DXA bone mineral density (BMD) measurements despite differences in absolute calibration. However, in clinical practice, raw BMD values (in g/cm²) are not normally used for assessing skeletal status and fracture risk. Instead, the BMD values are expressed in terms of the number of standard deviations above or below the young normal value (commonly referred to as theT-score). If the normative populations of the various systems are consistent, the standard deviation scores should also be consistent. For this reason, the World Health Organization (WHO) recently established diagnostic criteria for osteoporosis based onT-scores and not BMD. However, few studies have compared the instruments in terms of their standard deviation scores. In this study, we used linear regression to compareT-scores in 83 women at L1–4 and 120 women at the femoral neck obtained on a Lunar DPX and a Hologic QDR-1000/W system. Patient BMD andT-score measurements were highly correlated between the two systems (r>0.95). No clinically significant difference in L1–4T-scores was seen (less than 0.1 SD). However, linear regression analysis confirmed a systematic difference of 0.9 SD between the femoral neck T-scores. This discrepancy is caused by: (1) differences in the normal populations, and (2) differences in statistical models used to determine the young normal mean and standard deviation. In an attempt to correct the discrepancy, the female young normal mean and standard deviation were recalculated for the femoral neck using published epidemiological data from NHANES and existing DXA cross-calibration equations. The Hologic young normal value (mean ± SD) was redefined as 0.85±0.11 g/cm², while the Lunar value was redefined as 1.00±0.11 g/cm². When the femoral neckT-scores for the study population were recalculated on the basis of these new values, the results were equivalent between manufacturers, effectively eliminating the discrepancy. However, the revised values should be confirmed by additional measurements in young normal adults.     

Cross-calibration of dual-energy X-ray densitometers for a large, multi-center genetic study of osteoporosis

Osteoporosis is a common disease with a strong genetic component characterized by reduced bone mass and an increased risk of fragility fractures. Bone mineral density (BMD) is the most important determinant of osteoporotic fracture risk, but the genes responsible for BMD regulation and fracture are incompletely defined. To enable multi-center studies to examine the genetic influences on BMD there is a requirement to standardize measurements across different manufacturers of bone densitometers, different versions of machines and different normative ranges. This paper describes a method developed to allow near-identical subjects with low age-adjusted BMD (based on Z-scores) to be recruited in 17 centers using 27 different densitometers. Cross-calibration was based on measurements using a European spine phantom circulated to all centers and measured ten times on each individual machine. From theses values an individual exponential curve, based on nominal versus observed BMD, was derived for each machine. As expected, there were large and significant variations in nominal BMD values, not only between scanners from different manufacturers but also between different versions of scanners from the same manufacturer. Hologic scanners tended to underestimate the nominal BMD, while Lunar scanners overestimated the value. Norland scanners gave mixed values over estimating BMD at the lower nominal value (0.5 g/cm²) while underestimating the value at the higher value (1.5 g/cm²). The validity of the exponential equations was tested using hip and spine measurements on 991 non-proband women from a familial osteoporosis study (FAMOS). After cross-calibration there was a considerable reduction in variation between machines. This observation, coupled with the absence of a similar reduction in variation attributable to a linear regression on age, demonstrated the validity of the cross-calibration approach. Use of the cross-calibration curves along with a standard normative range (in the case of this study, the Hologic normative range) allowed age-specific Z-scores to be used as an inclusion criterion in this genetic study, a method that will be useful for other trials where age-specific BMD inclusion criteria are required.     

International variation in proximal femur bone mineral density

Summary

We observed higher proximal femur bone mineral density (BMD) in European women compared to average values derived from US Caucasian women in the National Health and Nutrition Examination Survey (NHANES) study. Across European centres, Parisian women had lower proximal femur BMD compared to women from Kiel or Sheffield.

Introduction

Proximal femur BMD of US adults (NHANES III) may not accurately reflect that of European women. We examined the heterogeneity of BMD across European and US Caucasian women and across different European populations.

Methods

Proximal femur BMD was measured in women ages 20–39 years (n?=?258) and 55–79 years (n?=?1,426) from three European centres. Cross-calibrated BMD for total hip, femoral neck, trochanter and intertrochanter were examined. International variation in BMD was assessed by comparing means and SDs in the European data with those from the US NHANES III study. European populations were stratified into 5-year age bands to establish individual centre reference intervals. Between-centre differences were assessed using ANOVA and post hoc Fisher’s least significant difference tests.

Results

European women had higher BMD than US women: The differences were 7.1% to 14.2% (p?<?0.001) and 0% to 3.9% (p?<?0.05) in the older and younger women, respectively. Standard deviations for BMD at the different sites were comparable to those for US women. Among older, but not younger European women, proximal femur BMD was significantly lower in French women (Paris) than in women from Germany (Kiel) or the UK (Sheffield) (difference?=?5.0% to 9.6%, p?<?0.05).

Conclusions

International variation in hip BMD does exist, with international and between-centre differences being less evident at the femoral neck.     

Bone mineral density in Norwegian premenopausal women

The aims of this study were: 1) to determine bone mineral density (BMD) in different age groups, 2) to determine the prevalence of low BMD, and 3) to determine the possible association between BMD and a number of risk factors in Norwegian premenopausal women. BMD of the lumbar spine (L₂–L₄), total body, and the hip (total femur, femur neck, and trochanter) were measured using dual-energy X-ray absorptiometry (Prodigy, Lunar) in 145 randomly selected women aged 13–39 years. Information on other factors thought to influence BMD was obtained through questionnaire and a clinical interview. The group aged 25–29 years had the highest mean BMD in the total body, lumbar spine, and total femur while the group aged 13–19 years had the highest mean BMD in the femur neck and the trochanter. The mean BMD values of Norwegian premenopausal women were 3.4–5.1% higher than US/European reference data (P<0.05). Five percent of the study sample aged 20–39 years were defined with low BMD (Z-score <–2) using the standard values from this study. Weight-bearing physical activity, body weight, body height, and age were positively associated with BMD, whilst menstrual dysfunction and previous pregnancy were associated with lower BMD in some of the measurement sites. The results show that the factors associated with BMD are extensive, and the strategies to prevent low BMD have to be multifactorial. A follow-up study should be conducted on the study sample to investigate actual mean BMD values and BMD changes through time.     

Sexual differences in bone markers and bone mineral density of normal Chinese

We measured bone mineral density (BMD) at lumbar (L2–L4) vertebrae and proximal femurs of 385 healthy Chinese women aged 40–70 years and 156 healthy Chinese men aged 20–85, and four markers—bone alkaline phosphatase isozyme (BAP), procollagen-I C terminal propeptide (PICP), osteocalcin (BGP) in serum, and a bone resorption marker, urinary cross-linked N-telopeptide of type I collagen (NTX), of these subjects. The results indicate that in postmenopausal women, levels of all the markers increased with age. In men, serum BAP, PICP, and urinary NTX decreased significantly, and serum BGP decreased with borderline significance (P=0.08). With increasing age, bone density decreased at both sites in post-menopausal women and at the proximal femur in men. The lumbar bone density showed no significant age-related changes in men. In premenopausal women, BMD at either site showed no significant change with increasing age. Despite the different trends between men and women of agerelated changes in BMD and bone markers, bone density of both proximal femur and spine in both sexes correlated inversely with levels of the bone markers in a manner independent of age or body weight. The meaning of opposite age effects on bone markers in men and women needs further investigation. In addition, higher bone marker levels, implying faster bone turnover rate, are associated with lower BMD in both sexes.     

Standardization of Bone Mineral Density at Femoral Neck, Trochanter and Ward’s Triangle

The International Committee for Standards in Bone Measurement (ICSBM) has published standardization formulas for total hip bone mineral density (BMD). In many applications, however, BMD of hip subregions, such as femoral neck (FN), trochanter (TR), and Ward’s triangle (WT), are commonly measured. This paper addresses whether the standardization formulas for total hip BMD can be adequately used for hip subregions. We used data from 100 healthy women, from 20 to 80 years old, who had hip BMD measured in both the total hip and hip subregions by a Hologic QDR 2000, a Lunar DPX, and a Norland XR26 Mark II. The same women were used by ICSBM for the standardization of total hip BMD. In addition, we used data of 3139 patients from a clinical trial to validate our results. We derived standardization formulas for FN, TR, and WT using the same statistical method as that used for total hip BMD. We applied both total hip calibration formulas and subregion-specific formulas to the data and compared the corresponding effect. We found that the total hip calibration formulas can partially reduce BMD differences between the Hologic and Lunar as well as the Lunar and Norland scanners in hip subregions, but increase differences between the Hologic and Norland scanners. The subregion calibration formulas are most appropriate for calibrating subregion BMD values and their absolute changes, and should be adopted. Standardization is unnecessary for BMD percentage changes in our clinical trial data. Received: 9 September 1999 / Accepted: 11 October 1999     

Dissimilar Spine and Femoral Z-Scores in Premenopausal Women

The purpose of this study was to determine if differences exist in premenopausal women between z-scores for lumbar spine and proximal femoral bone mineral densities (BMD). Participants were 237 women ranging in age from 20 to 45 years. BMDs of the lumbar spine and proximal femur (femoral neck, Ward's area, and trochanter) were assessed using dual-energy X-ray absorptiometry (Lunar DPX). Mean (±SD) age, height, and weight of the participants were 29.4 ± 6.9 years, 164.4 ± 6.1 cm, and 64.9 ± 12.1 kg, respectively. Lumbar spine BMD and BMD at the femoral neck, Ward's area, and trochanter were significantly correlated with large SEEs (r = 0.59–0.65; SEE = 0.09–0.11). No positive correlation with age and BMD at any site was seen in this population but a significant negative correlation with age was seen in the proximal femur beginning at age 30. Twenty to 24% of the 20–29-year-olds exhibited a difference in z-scores of greater than 1 between the spine and sites in the proximal femur. This percentage increased to 32–46% in the 30–45-year-olds but the nature of the observed differences changed. The differences in spine and proximal femoral z-scores that are seen in the older age group appear to be the result of the earlier onset of bone loss in the proximal femur rather than an initial difference in peak bone mass which has been maintained. Received: 28 August 1996 / Accepted: 25 April 1997