A Pediatric Bone Mass Scan has Poor Ability to Predict Peak Bone Mass: An 11-Year Prospective Study in 121 Children

Purpose: This 11-year prospective longitudinal study examined how a pre-pubertal pediatric bone mass scan predicts peak bone mass. Methods: We measured bone mineral content (BMC; g), bone mineral density (BMD; g/cm2) and bone area (cm2) in femoral neck, total body and lumbar spine by dual energy X-ray absorptiometry (DXA) in a population based cohort including 65 boys and 56 girls. At baseline all participants were pre-pubertal with a mean age of 8 years (range 6-9), they were re-measured at a mean 11 years (range 10-12) later. The participants were then mean 19 years (range 18-19), an age range that corresponds to peak bone mass in femoral neck in our population. We calculated individual BMC, BMD and bone size Z-scores, using all participants at each measurement as reference and evaluated correlations between the two measurements. Individual Z-scores were also stratified in quartiles to register movements between quartiles from pre-pubertal age to peak bone mass. Results: The correlation coefficients (r) between pre-pubertal and young adulthood measurements for femoral neck BMC, BMD and bone area varied between 0.37-0.65. The reached BMC value at age 8 years explained 42% of the variance in the BMC peak value, the corresponding values for BMD was 31% and bone area 14%. Among the participants with femoral neck BMD in the lowest childhood quartile, 52% had left this quartile at peak bone mass. A pediatric bone scan with a femoral neck BMD value in the lowest quartile had a sensitivity of 47% (95% CI 28, 66) and a specificity of 82% (95% CI 72, 89) to identify individuals who would remain in the lowest quartile at peak bone mass. Conclusions: The pre-pubertal femoral neck BMD explained only 31% of the variance in femoral neck peak bone mass. A pre-pubertal BMD scan in a population based sample has poor ability to predict individuals who are at risk of low peak bone mass.