Accrual of Bone Mass in Children and Adolescents With Cystic Fibrosis

Context: Low bone density is a complication of cystic fibrosis (CF). Hypothesis: Accrual of bone mass is most impaired in the sickest children, as judged by nutritional status and pulmonary function. Design: Retrospective analysis of correlation between lumbar spine bone mineral density (BMD), body mass index (BMI), and forced expiratory volume in 1 second (FEV1) z scores in children and adolescents with CF. Setting: Pediatric hospital specialist CF service. Patients: Sixty participants aged 5.9 to 18.8 years (24 female) with confirmed CF. Interventions: Lumbar spine BMD, BMI, and FEV1 z scores measured at first BMD scan; 40 participants had sequential scans. Change in L1-L4 z scores over time was used as a measure of bone accrual, and BMI as a measure of nutritional status. Outcome Measures: Correlations between lumbar spine BMD, BMI, and FEV1 z scores. Results: Mean BMI and BMD z scores were strongly correlated at the initial scan (P < 0.0001), suggesting that nutritional status is a major determinant of BMD. In the sequential scan at a mean age of 16.1 years, height centile was maintained, indicating normal linear growth. Changes in BMI and BMD z scores were positively correlated (P = 0.001), indicating that patients failing to gain weight appropriately with growth were also failing to acquire bone normally. Change in FEV1 z score was correlated with change in both BMD (P < 0.0001) and BMI z scores (P = 0.02). Conclusion: Although young people with CF may be maintaining normal growth in height, bone accrual is impaired in those with the poorest nutritional status and lung function.