Up to 100 subjects, both non-CF volunteers and Cystic Fibrosis (CF) patients, will participate in a single study visit that will include a DEXA scan (if not completed as standard of care within 6 months prior to research visit), micro CT, and blood collection.

Approximately 10 subjects with CF that have completed the main study and have results which indicate bone disease are eligible to participate in the sub study. Subjects who consent will receive treatment with denosumab (60 mg/ml via subcutaneous injection in the upper arm, upper thigh, or abdomen every 6 months) for up to 5 years. These subjects will be asked to return every 6 months for injections and annually (+/- 6 months) for up to 5 years for a DEXA scan, micro CT, and blood collection.

treatment with denosumab every 6 months for up to 5 years

Z and/or T scores

Trabecular bone volume to tissue volume (BV/TV), cortical and trabecular thickness (Tb.Th, microns), trabecular spacing (Tb.Sp; microns), and structure model index (SMI; index of trabecular rod vs plate-like shape/ stoutness) will be assessed. Change in BV/TV and cortical thickness will be taken to indicate increased/decreased bone mass accrual by microCT.