Correlates of osteopenia in patients with cystic fibrosis.

OBJECTIVE

As the expected survival improves for individuals with cystic fibrosis, these individuals face myriad medical complications. The goals of this study were to examine the prevalence of osteopenia in children and adults with cystic fibrosis and to elucidate the risk factors associated with deficits in bone mineral.

METHODOLOGY

We compared bone mineral levels in 49 patients (30 female and 19 male) ages 8 through 48 years with those of age- and sex-matched control subjects. Lumbar spine, femoral neck, and whole-body bone mineral were measured by dual-energy radiographic absorptiometry and expressed in terms of bone mineral content, areal bone density (BMD), and bone mineral apparent density (BMAD), which corrects for differences in bone size. Clinical variables were evaluated as potential correlates of bone mineral.

RESULTS

Patients with cystic fibrosis had significantly less bone mineral than did control subjects at all sites using all expressions of bone mass. Mean BMD z scores were -1.7 (lumbar spine), -1.9 (femoral neck), and -1.2 (whole body). BMAD z scores also were significantly low for age and gender. Twenty-six of the 49 patients (8 adolescents) had significant osteopenia according to their BMD z scores; 14 of the 45 patients (5 adolescents) with available BMAD z scores had significantly low values at one or more sites. Age, pubertal stage, body mass, caloric expenditure, illness severity, glucocorticoid therapy, and gonadal function predicted bone mineral status. Serum parathyroid hormone and calcium, carbohydrate intake, and weight-bearing activity had limited predictive value. Daily calcium intake and cystic fibrosis transmembrane regulator genotype did not predict bone mineral status.

CONCLUSIONS

Osteopenia is common at all ages in cystic fibrosis, suggesting that inadequate bone mineral accretion as well as increased bone loss contribute to the deficits in bone mineral observed. Several clinical factors seem to contribute to these deficits.