Long-term versus short-term precision of dual-energy X-ray absorptiometry scans and the impact on interpreting change in bone mineral density at follow-up

Cross-calibration, Least Significant Change and Quality Assurance in Multiple Dual-Energy X-ray Absorptiometry Scanner Environments: 2019 ISCD Official Position

In preparation for the International Society for Clinical Densitometry Position Development Conference (PDC) 2019 in Kuala Lumpur, Malaysia, a cross-calibration and precision task force was assembled and tasked to review the literature, summarize the findings, and generate positions to answer 4 related questions provided by the PDC Steering Committee, which expand upon the current ISCD official positions on these subjects. (1) How should a provider with multiple dual-energy X-ray absorptiometry (DXA) scanners of the same make and model calculate least significant change (LSC)? (2) How should a provider with multiple DXA systems with the same manufacturer but different models calculate LSC? (3) How should a provider with multiple DXA systems from different manufacturers and models calculate LSC? (4) Are there specific phantom procedures that one can use to provide trustworthy in vitro cross calibration for same models, different models, and different makes? Based on task force deliberations and the resulting systematic literature reviews, 3 new positions were developed to address these more complex scenarios not addressed by current official positions on single scanner cross calibration and LSC. These new positions provide appropriate guidance to large multiple DXA scanner providers wishing to offer patients flexibility and convenience, and clearly define good clinical practice requirements to that end.

Repeating Measurement of Bone Mineral Density when Monitoring with Dual-energy X-ray Absorptiometry: 2019 ISCD Official Position

Bone mineral density (BMD) can be measured at multiple skeletal sites using various technologies to aid clinical decision-making in bone and mineral disorders. BMD by dual-energy X-ray absorptiometry (DXA) has a critical role in predicting risk of fracture, diagnosis of osteoporosis, and monitoring patients. In clinical practice, DXA remains the most available and best validated tool for monitoring patients. A quality baseline DXA scan is essential for comparison with all subsequent scans. Monitoring patients with serial measurements requires technical expertise and knowledge of the least significant change in order to determine when follow-up scans should be repeated. Prior ISCD Official Positions have clarified how and when repeat DXA is useful as well as the interpretation of results. The 2019 ISCD Official Positions considered new evidence and clarifies if and when BMD should be repeated. There is good evidence showing that repeat BMD measurement can identify people who experience bone loss, which is an independent predictor of fracture risk. There is good evidence showing that the reduction in spine and hip fractures with osteoporosis medication is proportional to the change in BMD with treatment. There is evidence that measuring BMD is useful following discontinuation of osteoporosis treatment. There is less documentation addressing the effectiveness of monitoring BMD to improve medication adherence, whether monitoring of BMD reduces the risk of fracture, or effectively discriminates patients who should and should not recommence treatment following an interruption of medication. Further research is needed in all of these areas.

Same-Day Vs Consecutive-Day Precision Error of Dual-Energy X-Ray Absorptiometry for Interpreting Body Composition Change in Resistance-Trained Athletes

The application of dual-energy X-ray absorptiometry (DXA) in sport science settings is gaining popularity due to its ability to assess body composition. The International Society for Clinical Densitometry (ISCD) recommends application of the least significant change (LSC) to interpret meaningful and true change. This is calculated from same-day consecutive scans, thus accounting for technical error. However, this approach does not capture biological variation, which is pertinent when interpreting longitudinal measurements, and could be captured from consecutive-day scans. The aims of this study were to investigate the impact short-term biological variation has on LSC measures, and establish if there is a difference in precision based on gender in a resistance-trained population. Twenty-one resistance-trained athletes (age: 30.6 ± 8.2 yr; stature: 174.2 ± 7.2 cm; mass: 74.3 ± 11.6 kg) with at least 12 mo consistent resistance training experience, underwent 2 consecutive DXA scans on 1 d of testing, and a third scan the day before or after. ISCD-recommended techniques were used to calculate same-day and consecutive-day precision error and LSC values. There was high association between whole body (R² = 0.98-1.00) and regional measures (R² = 0.95-0.99) for same-day (R² = 0.98-1.00), and consecutive-day (R² = 0.95-0.98) measurements. The consecutive-day precision error, in comparison to same-day precision error, was significantly different (p < 0.05), and almost twice as large for fat mass (1261 g vs 660 g), and over 3 times as large for lean mass (2083 g vs 617 g), yet still remained within the ISCD minimum acceptable limits for DXA precision error. No whole body differences in precision error were observed based on gender. When tracking changes in body composition, the use of precision error and LSC values calculated from consecutive-day analysis is advocated, given this takes into account both technical error and biological variation, thus providing a more accurate indication of true and meaningful change.

Utility of DXA for monitoring, technical aspects of DXA BMD measurement and precision testing

Monitoring a patient's bone mineral density (BMD) is one of the main reasons for dual-energy X-ray absorptiometry (DXA) referral. It is widely recommended by clinical guidelines, and the accepted standard in practice for managing patients with osteoporosis and other disorders. Clinicians and DXA providers must be familiar with the scientific rationale and procedures involved in measurement science to obtain accurate and reproducible results. Their importance is critical to maximise the value of scan acquisition and interpretation. Scanning individual patients, with different needs and disorders, requires excellence in training, experience, and is more complex than just simply 'measuring BMD'. Over the past 3 decades many studies have validated the importance of monitoring BMD for fracture risk assessment, and for patients on osteoporosis treatment. New DXA features enhance the value of DXA monitoring today. Quality BMD measurement remains an essential component of patient care in osteoporosis and other disorders, playing a critical role in informed decision making for clinicians assessing and managing their patients. In this article we describe some of the technical aspects of measurement and discuss the utility of DXA for monitoring patients in clinical practice.

The characteristics of osteoporotic patients in Graves' disease patients newly diagnosed after menopause: a prospective observational study

Overt hyperthyroidism is associated with reduced bone density. The extent of restoration of reduced bone density caused by hyperthyroidism in postmenopausal Graves' disease (GD) patients has not fully been investigated. We examined 85 newly diagnosed postmenopausal GD patients, and we measured their serum thyroid hormone levels as well as their bone turnover marker levels and the bone mineral density (BMD) of their lumbar spine (LS), both femoral necks (FN), and left distal radius (DR). We prospectively observed the patients for changes in BMD and bone turnover marker levels during a 24-month period after euthyroidism had been established by ATD treatment. The median age of the subjects was 57 years old (range: 50 to 79). 46 (54.1%) patients had osteoporosis. 42 of the 46 osteoporosis patients had low BMD in the DR. The patients with osteoporosis were significantly older, had a significantly lower BMI, and had significantly higher bone turnover marker levels compared to the normal BMD patients. The best predictor of the BMD in the DR was BMD in the FN (β = 0.40, p < 0.0001). A total of 42 patients were followed up for 24 months after attainment of euthyroidism, and 19 of them were osteoporosis at the first visit. The BMD of the 19 osteoporotic patients had increased by 4.9% in the LS, 11.9% in the FN, and 9.3% in the DR at 24 months. After maintaining a euthyroid state for 24 months by means of ATD treatment, 26% of the osteoporotic patients had recovered from osteoporosis.

An Advanced Quantitative Echosound Methodology for Femoral Neck Densitometry

The aim of this paper was to investigate the clinical feasibility and the accuracy in femoral neck densitometry of the Osteoporosis Score (O.S.), an ultrasound (US) parameter for osteoporosis diagnosis that has been recently introduced for lumbar spine applications. A total of 377 female patients (aged 61-70 y) underwent both a femoral dual X-ray absorptiometry (DXA) and an echographic scan of the proximal femur. Recruited patients were sub-divided into a reference database used for ultrasound spectral model construction and a study population for repeatability assessments and accuracy evaluations. Echographic images and radiofrequency signals were analyzed through a fully automatic algorithm that performed a series of combined spectral and statistical analyses, providing as a final output the O.S. value of the femoral neck. Assuming DXA as a gold standard reference, the accuracy of O.S.-based diagnoses resulted 94.7%, with k = 0.898 (p < 0.0001). Significant correlations were also found between O.S.-estimated bone mineral density and corresponding DXA values, with r(2) up to 0.79 and root mean square error = 5.9-7.4%. The reported accuracy levels, combined with the proven ease of use and very good measurement repeatability, provide the adopted method with a potential for clinical routine application in osteoporosis diagnosis.

Effect of Clothing on Measurement of Bone Mineral Density

It is unknown whether allowing patients to have BMD (bone mineral density) studies acquired while wearing radiolucent clothing adlib contributes appreciably to the measurement error seen. To examine this question, a spine phantom was scanned 30 times without any clothing, while draped with a gown, and while draped with heavy winter clothing. The effect on mean BMD and on SD (standard deviation) was assessed. The effect of clothing on mean or SD of the area was not significant. The effect of clothing on mean and SD for BMD was small but significant and was around 1.6% for the mean. However, the effect on BMD precision was much more clinically important. Without clothing the spine phantom had an least significant change of 0.0077 gm/cm(2), while when introducing variability of clothing the least significant change rose as high as 0.0305 gm/cm(2). We conclude that, adding clothing to the spine phantom had a small but statistically significant effect on the mean BMD and on variance of the measurement. It is unlikely that the effect on mean BMD has any clinical significance, but the effect on the reproducibility (precision) of the result is likely clinically significant.

New perspectives in echographic diagnosis of osteoporosis on hip and spine

Currently, the accepted "gold standard" method for bone mineral density (BMD) measurement and osteoporosis diagnosis is dual-energy X-ray absorptiometry (DXA). However, actual DXA effectiveness is limited by several factors, including intrinsic accuracy uncertainties and possible errors in patient positioning and/or post-acquisition data analysis. DXA employment is also restricted by the typical issues related to ionizing radiation employment (high costs, need of dedicated structures and certified operators, unsuitability for population screenings). The only commercially-available alternative to DXA is represented by "quantitative ultrasound" (QUS) approaches, which are radiation-free, cheaper and portable, but they cannot be applied on the reference anatomical sites (lumbar spine and proximal femur). Therefore, their documented clinical usefulness is restricted to calcaneal applications on elderly patients (aged over 65 y), in combination with clinical risk factors and only for the identification of healthy subjects at low fracture risk. Literature-reported studies performed some QUS measurements on proximal femur, but their clinical translation is mostly hindered by intrinsic factors (e.g., device bulkiness). An innovative ultrasound methodology has been recently introduced, which performs a combined analysis of B-mode images and corresponding "raw" radiofrequency signals acquired during an echographic scan of the target reference anatomical site, providing two novel parameters: Osteoporosis Score and Fragility Score, indicative of BMD level and bone strength, respectively. This article will provide a brief review of the available systems for osteoporosis diagnosis in clinical routine contexts, followed by a synthesis of the most promising research results on the latest ultrasound developments for early osteoporosis diagnosis and fracture prevention.

Does the precision of dual-energy X-ray absorptiometry for bone mineral density differ by sex?

Given larger bone size in men, bone mineral density (BMD) precision might differ between sexes. This study compared dual-energy X-ray absorptiometry BMD precision of 3 International Society for Clinical Densitometry-certified technologists in older men and women. Each technologist scanned a cohort of 30 men and 30 women (total n = 180) by using a Lunar iDXA densitometer (GE Healthcare, Madison, WI). Each volunteer had 2 lumbar spine and bilateral hip scans with repositioning between examinations. BMD least significant change was calculated. Age and body mass index did not differ between men and women. Mean height and weight were greater in men, 174.6 cm ± 6.9 and 81.6 kg ± 11.1 respectively, (p < 0.0001) than in women, 161.5 cm ± 5.9/69.1 kg ± 14.2, respectively. Bone area was greater in men (p < 0.0001) at all sites. BMD least significant change was statistically better (p < 0.05) in women at the mean total femur (0.014 vs 0.018 g/cm(2)) and left femoral neck (0.025 vs 0.038 g/cm(2)), but not different at either total femur, the right femoral neck, or lumbar spine (all p > 0.05). In conclusion, statistically significant male/female differences in BMD precision were observed at the mean total femur and left femoral neck. Given the small magnitude of difference in g/cm(2) and inconsistent pattern, that is, no right femoral neck difference, there is virtually no clinical difference in BMD precision between sexes. These data do not support a need for sex-specific precision analyses.