DXA Assessment in Gender Diverse Youth

Purpose/Aims

Evaluate DXA in gender diverse youth and examine interpretation of results using male and female reference values.

Rationale/Background

Gender affirming care in the US has increased over the past decade. Positions on DXA interpretation in gender diverse (GD) adults exist; guidelines for GD youth are being developed. Standard practice for prepubescent children seeking gender affirming medical care is to start pubertal suppression (PS). Bone mass accrual in the growing skeleton occurs during puberty and the impact of PS on bone mineral density (BMD) is unclear. We examine the practice of reporting results using both male and female norms.

Methods

Retrospective review of clinically obtained DXAs and clinical information regarding gender affirming medical care including PS, hormonal replacement therapy (HRT), Tanner score at DXA, fracture history, serum 25(OD)D level, and other bone or nutritional issues in children (< 18 years) seen at our children's hospital prior to 1/11/2023. All had at least one DXA. BMD and z-score for total body less head (TBLH), lumbar spine (LS), and lateral distal femurs (LDF) regions 1 – 3 for both sexes were evaluated. Height-adjusted z-score (HAZ) was used for TBLH and LS. Serial DXA was assessed if available. We evaluated z-score patterns at all body sites comparing natal norms to opposite sex norms.

Results

Twenty-four GD children (12 natal female) with a mean age at first DXA of 13.1 years (9.9 to 17) were identified. Twenty-three received PS and 12 received HRT. Half had insufficient/deficient 25(OH)D status, and 33% had history of fracture, consistent with the general pediatric population. All had TBLH and LS; 23 had LDF scans. At first DXA, 13 of 24 (6 natal female) were on PS. Mean age of PS initiation differed by natal sex with girls starting at 12.4 years and boys starting at 14.7 years. Three patients received HRT; all had received PS. When comparing z-scores using both sex normative standards, only the LS showed consistent differences between the sexes: z-scores were lower in natal males using female norms and higher in natal females using male norms. Difference in z-scores varied at all other body sites between the sexes with no trend.

Implications

ISCD adult positions for transgender patients advises use of assigned gender reference values for calculation of z-scores. Utilizing this adult position creates problems for interpretation of DXA in children because z- scores are used in pediatrics and bone mass accrual and growth vary by sex and age. PS decreases growth trajectory and BMD further complicating interpretation of results and use of pediatric reference values.

Analyzing BMD results using both sex norms, using recommended size adjustments to BMD in pediatrics, and providing this information to the treating clinician for consideration of clinical context provides the most complete picture. Development of a standardized DXA report for GD youth containing dual normative results will aid in reporting. For serial measures, standardized reports should emphasize serial BMD changes rather than z-scores.