Position StatementDual Energy X-ray Absorptiometry Interpretation and Reporting in Children and Adolescents: The 2007 ISCD Pediatric Official Positions
Introduction
The foundation of bone health is built during the childhood and teenage years 1, 2, 3, 4. Peak bone mass is established by the third decade of life 2, 3, 4, 5, 6, 7, 8, a compromise of which may be associated with an increased lifetime risk of osteoporosis and fractures 9, 10. A variety of childhood diseases and pharmaceutical interventions can result in bone loss, suboptimal accrual of bone mass, or a combination of both 11, 12, 13, 14, 15, 16. Therefore, clinicians have sought to identify tests that best evaluate bone health in young children and adolescents. The goal of bone densitometry is to identify individuals at risk for skeletal fragility, to determine whether bone mass is compromised in children with established bone fragility, and to guide and monitor treatment. Although the rationale for densitometry is the same in children as in adults, performance of densitometry and interpretation of bone density results are much more complex in young, growing patients 3, 4, 17, 18, 19.
Dual-energy X-ray absorptiometry (DXA) is the most commonly used bone densitometric technique for children throughout the world, preferred over other techniques because of its speed, precision, safety, low cost, and widespread availability 3, 4, 19, 20, 21. In contrast to adults, there are no internationally recognized guidelines for bone density testing in children. For a given patient, the clinician must consider the need for a bone density evaluation, including both the duration and severity of the chronic illness, and/or frequency and nature of fractures (19). There are significant knowledge gaps in this area, few large representative normative databases from healthy youth, especially for certain ethnic groups, and a lack of consensus as to which adjustments may be needed to interpret densitometric results in children with altered growth or maturity patterns. Appendicular fractures exhibit a bimodal distribution with an initial peak during puberty (at 11 yr in girls and 14 yr in boys) (22). Such fractures were originally attributed to trauma due to increased activity in this age group, although more recent studies have suggested that such fractures may reflect differential changes in bone mineral content (BMC) and bone area during puberty, possibly resulting in transient bone fragility (23). Furthermore, a four-year follow-up study of children with forearm fractures and low bone mass demonstrated a persistently low BMC at several skeletal sites, even after adjustment for bone area, height, weight and pubertal stage, confirming the premise that fractures may indeed represent a marker of skeletal fragility (24). Although still limited, there are mounting data that describe the relationship between DXA measurements and fracture risk in growing children and adolescents. All of the prospective studies completed to date in this area have examined otherwise healthy children or adolescents with fractures, rather than those with chronic disease 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43.
The following questions regarding the reporting of pediatric densitometry results were addressed at the 2007 International Society for Clinical Densitometry (ISCD) Position Development Conference, held in Montreal, Canada, and the results follow:
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What are the most appropriate and reproducible sites for densitometry in children?
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What is the best method for reporting areal bone mineral density (BMD) in children (what corrections should be made for bone size, height, lean body mass, skeletal age or pubertal stage)?
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What are the most appropriate normative databases for use in childhood?
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What are the elements that should be included in a DXA report for a child or adolescent?
Section snippets
Methodology
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 positions were rated by the Expert Panel on quality of evidence (Good; Fair; Poor: where Good is evidence that includes results from well-designed, well-conducted studies in representative populations; Fair is evidence sufficient to determine effects on outcomes, but the strength of the evidence is limited by the number,
ISCD Official Position
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DXA is the preferred method for assessing BMC and areal BMD.
Grade: Good-B-W-Necessary
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The posterior-anterior (PA) spine and total body less head (TBLH), are the most accurate and reproducible skeletal sites for performing BMC and areal BMD measurements.
Grade: Good-B-W-Necessary
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Soft tissue measures in conjunction with whole body scans may be helpful in evaluating patients with chronic conditions associated with malnutrition, such as anorexia nervosa, inflammatory bowel disease, cystic fibrosis,
ISCD Official Positions
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In children with linear growth or maturational delay, spine and TBLH BMC and areal BMD results should be adjusted for absolute height or height age, or compared to pediatric reference data that provide age-, gender- and height-specific Z-scores.
Grade: Good-A-W-Necessary
ISCD Official Positions
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An appropriate reference data set must include a sample of the general healthy population sufficiently large to characterize the normal variability in bone measures that takes into consideration gender, age and race/ethnicity.
Grade: Good-A-W-Necessary
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When upgrading densitometer instrumentation or software, it is essential to use reference data valid for the hardware and software technological updates.
Grade: Good-A-W-Necessary
ISCD Official Positions
Baseline DXA testing
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Baseline DXA reports should contain the following information:
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DXA manufacturer, model and software version
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Referring physician
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Patient age, gender, race/ethnicity, weight and height
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Relevant medical history including previous fractures
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Indication for study
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Bone age results, if available
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Technical quality
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BMC and areal BMD
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BMC and areal BMD Z-score
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Source of reference data for Z-score calculations
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Adjustments made for growth and maturation
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Interpretation
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Recommendations for the necessity
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Additional Questions for Future Research
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Which DXA sites and various adjustments for lean mass, pubertal stage, height, and bone size (BMAD) best predict fracture in healthy children and children with chronic disease?
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How can available pediatric reference databases be kept up to date? How often should they be updated? What adjustments can be made when newer software versions become available?
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Is there a need to consider “universal DXA units,” considering the variability among scanners from differing manufacturers and that normative data
Summary
The ISCD Official Positions on the interpretation and reporting of densitometry in children and adolescents represents an effort to consolidate opinions on which skeletal sites should be assessed, which corrections should be made in these assessments, appropriate pediatric reference databases, and the important elements to include in a DXA report. Opinions from pediatric bone health experts from around the world were elicited and a systematic literature search performed. Given the sparse data
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