Dual-Energy X-Ray Absorptiometry Interpretation and Reporting in Children and Adolescents: The Revised 2013 ISCD Pediatric Official Positions

Abstract

The International Society for Clinical Densitometry Official Revised Positions on reporting of densitometry results in children represent current expert recommendations to assist health care providers determine which skeletal sites should be measured, which, if any, adjustments should be made, reference databases to be used, and the elements to include in a dual-energy X-ray absorptiometry report. The recommended scanning sites remain the total body less head and the posterior-anterior spine. Other sites such as the proximal femur, lateral distal femur, lateral vertebral assessment, and forearm are discussed but are only recommended for specific pediatric populations. Different methods of interpreting bone density scans in children with short stature or growth delay are presented. The use of bone mineral apparent density and height-adjusted Z-scores are recommended as suitable size adjustment techniques. The validity of appropriate reference databases and technical considerations to consider when upgrading software and hardware remain unchanged. Updated reference data sets for all contemporary bone densitometers are listed. The inclusion of relevant demographic and health information, technical details of the scan, Z-scores, and the wording “low bone mass or bone density” for Z-scores less than or equal to −2.0 standard deviation are still recommended for clinical practice. The rationale and evidence for the development of the Official Positions are provided. Changes in the grading of quality of evidence, strength of recommendation, and worldwide applicability represent a change in current evidence and/or differences in opinion of the expert panelists used to validate the position statements for the 2013 Position Development Conference.

Introduction

Assessment of pediatric bone density is an evolving specialty. Although there have been many advances over the last 6 yr since the publication of the original International Society for Clinical Densitometry (ISCD) recommendations for children and adolescents (1), there are still many areas where significant uncertainties exist. These revised recommendations reflect developments in the pediatric bone field related to the assessment of bone health and their impact on the issues related to reporting and interpreting pediatric densitometry results.

It has been clearly established that the foundation of adult bone health is built during the childhood and teenage years 2, 3, 4, 5. Peak bone mass is established by the third decade 4, 6, 7, 8, 9, a compromise of which may be associated with an increased lifetime risk of osteoporosis and fractures 10, 11. A variety of childhood diseases and pharmaceutical interventions can result in bone loss, suboptimal accrual of bone mass, or a combination of both 12, 13, 14, 15, 16, 17. 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, determine the magnitude of compromised bone mass in children with established bone fragility, and guide and monitor treatment. Although the rationale for densitometry is the same in children as adults, performing and interpreting bone density results is much more complex in young growing patients 4, 5, 18, 19, 20.

Dual-energy X-ray absorptiometry (DXA) is the most commonly used densitometric technique for children throughout the world, preferred over other techniques because of its speed, precision, safety, low cost, and widespread availability 4, 5, 20, 21, 22. However, 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 (20). There are significant knowledge gaps in this area, such as the paucity of large representative normative databases from healthy youth, especially for certain ethnic groups, and the need for validated adjustment techniques that may be needed to interpret densitometric tests in children with altered growth or maturity patterns. There is also debate around the issue of whether it is appropriate to compare the bone density of a child with chronic disease with data obtained from healthy youth; the need for disease-specific reference databases has been questioned. Appendicular fractures exhibit a bimodal distribution with an initial peak during puberty (at 11 yr in girls and 14 yr in boys) (23). Such fractures were originally attributed to trauma because of 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 geometry during puberty, possibly resulting in transient skeletal fragility (24). Furthermore, a 4-yr follow-up study of children with forearm fractures and low bone mass at study entry demonstrated a 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 (25). Although still limited, there are increasing data that describe the relationship between DXA measurements and fracture risk in growing children and adolescents. However, all the prospective studies completed to date in this area have examined otherwise healthy children or adolescents with fractures, rather than those with chronic disease 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44.

The following questions regarding the reporting of pediatric densitometry results were revisited at the 2013 ISCD Pediatric Position Development Conference, in Baltimore, MD, USA:

• What are the most appropriate and reproducible sites for densitometry measures in children and adolescents?

• What is the best method for reporting areal bone mineral density (aBMD) in children?

• What corrections should be made for bone size, height, lean body mass (LBM), skeletal age, or pubertal stage?

• What are the most appropriate normative databases for use in childhood?

• What are the elements that should be included in a DXA report for a child or adolescent?

The methods used to develop, and grading system applied to the ISCD Official Positions, are presented in the Executive Summary that accompanies this task force document. In brief, all positions were graded on quality of evidence (good; fair; and poor: where “good” is evidence that includes results from well-designed and well-conducted studies in representative populations; “fair” is evidence sufficient to determine effects on outcomes, but strength of the evidence is limited by the number, quality, or consistency of the individual studies; and “poor” is evidence that is insufficient to assess the effects on outcomes because of limited number or power of studies, important flaws in their design or conduct, gaps in the chain of evidence, or information), strength of recommendation (A: B: or C: where “A” is strong recommendation supported by the evidence; “B” is a recommendation supported by the evidence; and “C” is a recommendation supported primarily by expert opinion), and applicability (worldwide = W or variable, according to local requirements = L). Changes to the grading of each of the position statements previously presented in the original 2008 document (1) represent a revision in the quality of evidence, the strength of recommendation, and its worldwide applicability. On the other hand, where there has been no change in evidence, the changes may reflect differences in opinions of an alternative group of expert panelists used to validate the position statements.