The etiology of bone disease in patients with CF is multifactorial and contributing factors include poor nutrition, decreased activity levels, poor absorption of vitamin D, chronic inflammation, and therapy with corticosteroids. Multiple studies have correlated BMD with clinical factors such as lung function, nutritional status, inflammation markers, clinical score, and frequency of antibiotic courses. Studies evaluating the relationship between inflammation markers and bone in CF patients have been somewhat mixed, although in general have shown an inverse relationship between inflammation and BMD, and a direct correlation between inflammation and increased bone resorption markers. Inflammation markers evaluated have included both acute-phase cytokines such as IL-6 and TNF-alpha, and the general marker CRP. There is some evidence that CFTR is expressed in bone cells such as osteoclasts, osteoblasts, and osteocytes, suggesting the potential for a bone phenotype in patients with CF. Most studies utilize DXA and demonstrate reduced BMD in patients with CF that is usually detectable starting in adolescence. Low BMD is nearly universal among adults with CF; however, results from studies evaluating BMD in children with CF have been variable.