Position StatementPeripheral Dual-Energy X-ray Absorptiometry in the Management of Osteoporosis: The 2007 ISCD Official Positions
Introduction
In 1963, Cameron and Sorensen developed a new method for testing bone density in vivo by passing a monochromatic one single energy phantom beam through bone and soft tissue (1) at a peripheral skeletal site. Since that time, approximately 20,000 central and 15,000 peripheral densitometers have been sold (K. Faulkner, personal communication) and utilized to measure human bone density both clinically and in research studies. Since 2001, the International Society for Clinical Densitometry (ISCD) has reviewed various aspects of peripheral densitometry 2, 3 including the use of forearm dual-energy X-ray absorptiometry (DXA) for diagnosis of osteoporosis and for serial monitoring (4).
The proliferation of bone densitometers using different technologies for measuring BMD at different skeletal sites, along with the absence of technology-specific guidelines, has created great uncertainty in applying the results to the management of patients in clinical practice. The acronym pDXA (peripheral dual-energy X-ray absorptiometry) is used to describe dedicated devices that are specifically designed to measure the BMD of peripheral skeletal sites using DXA. There is no fundamental difference in technology between peripheral and central DXA. pDXA is used to measure bone mineral density (BMD) at the forearm, finger phalanges and calcaneus. Radiographic absorptiometry (RA) and quantitative ultrasound (QUS) are other technologies for assessing skeletal health at peripheral skeletal sites. Radiographic absorptiometry and QUS will not be considered in this document.
Some advantages of pDXA compared to central DXA are that the instruments are smaller and more portable, requiring minimal space to operate, and they are less expensive. Also, since the measurement sites are a significant distance from radiation-sensitive organs, radiation doses are extremely small and even lower than the doses associated with central DXA of the hip and spine. Nevertheless, pDXA may be subject to radiation protection regulation in many countries.
Various pDXA devices have been shown to predict forearm, spine, hip and any osteoporotic fractures in elderly women. However, the body of evidence evaluating the ability of pDXA (or its precursors single-energy photon absorptiometry [SPA] in 1963, single-energy X-ray absorptiometry [SXA], and peripheral dual-energy photon absorptiometry [pDPA]) to predict fracture risk is not as substantial as might be expected for a methodology older than central DXA. The use of pDXA in clinical practice continues to be poorly defined. Peripheral BMD measurement technologies were extensively studied at the beginning of the era of quantitative evaluation of BMD, but their evaluation has diminished over the last 20 yr with the rise of central DXA measurements. Furthermore, many devices that were used in the past are no longer commercially available and those that remain have not been evaluated by well standardized methods (e.g., population based, cross-sectional studies, prospective studies).
The role of peripheral densitometry in clinical practice remains poorly defined. The ISCD pDXA Task Force reviewed the medical literature and proposed a set of operational recommendations for the clinical use of pDXA for the following five major topics:
- 1
pDXA and fracture risk assessment
- 2
pDXA and diagnosis of osteoporosis
- 3
pDXA and treatment initiation
- 4
pDXA and treatment monitoring
- 5
pDXA and quality assurance/quality control (QA/QC)
The task force did not consider other peripheral X-ray technologies such as RA and radiogrammetry to avoid any confusion with forearm, heel, or finger measurements assessed by pDXA.
Section snippets
Methodology
The ISCD pDXA Task Force reviewed the peer-reviewed medical literature using Medline and PubMed from 1960 to date. A bibliography of 174 papers was initially prepared by the pDXA Task Force and papers were added as required to enable review of specific topics. Only bibliographies in English language were considered.
The methods used to develop, and grading system applied to the ISCD Official Positions, are presented in the Executive Summary that accompanies this paper. In brief, all Official
ISCD Official Position
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For pDXA, bone density measurements from different devices cannot be directly compared.
Grade: Good-A-W-Necessary
ISCD Official Positions
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Measurement by validated pDXA devices can be used to assess vertebral and global fragility fracture risk in postmenopausal women, however its vertebral fracture predictive ability is weaker than central DXA and heel QUS. There is a lack of sufficient evidence to support this position for men.
Grade: Fair-B-W-Necessary
- •
For pDXA, different devices should be independently validated for fracture risk prediction by prospective trials or by demonstration of equivalence to a clinically validated device.
ISCD Official Position
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The WHO diagnostic classification can only be applied to DXA at the femur neck, total femur, lumbar spine, and the one-third (33%) radius region of interest measured by DXA or pDXA devices utilizing a validated young-adult reference database.
Grade: Good-A-W-Necessary
ISCD Official Positions
- •
Central DXA measurements at the spine and femur are the preferred method for making therapeutic decisions and should be used if possible. However, if central DXA cannot be done, pharmacologic treatment can be initiated if the fracture probability, as assessed by radius pDXA (or DXA) using device specific thresholds and in conjunction with clinical risk factors, is sufficiently high.
Grade: Fair-B-W-Necessary
- •
Radius pDXA in conjunction with clinical risk factors can be used to identify a
ISCD Official Position
- •
pDXA devices are not clinically useful in monitoring the skeletal effects of presently available medical treatments for osteoporosis.
Good-A-W-Necessary
ISCD Official Positions
- •
For pDXA, the report should combine the following standard elements:
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Date of test
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Demographics (name, date of birth or age, sex, race or ethnicity)
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Requesting provider
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Names of those receiving a copy of report
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Indications for test
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Manufacturer, and model of instrument and software version
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Measurement value(s)
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Reference database
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Skeletal site/region of interest
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Quality of test
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Limitations of the test including a statement that the WHO diagnostic classification cannot be applied to T-scores obtained from
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ISCD Official Positions
- •
For pDXA, device-specific education and training should be given to the operators and interpreters prior to clinical use.
Grade: Good-A-W-Necessary
- •
Quality control procedures should be performed regularly.
Grade: Good-A-W-Necessary
Summary
Although pDXA technology was developed many years ago, its use in the clinical setting is confused and discordant. The ISCD Official Positions described herein reflects the current state of knowledge regarding pDXA.
The clinical use and utility of pDXA to diagnose osteoporosis is justified particularly in situations where central DXA is unavailable. Peripheral DXA measures are related to global fracture risk with similar relative risk as other central bone density ROI for postmenopausal women.
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