Factors associated with low bone mineral density in patients with cystic fibrosis.

Osteoporosis associated with cystic fibrosis is becoming more important as the life expectancy of patients continues to improve. This study was done to determine the prevalence of osteoporosis and osteopenia in CF patients and to identify risk factors. We reviewed the medical charts of 103 adults and adolescents with Cystic Fibrosis who had undergone a dual energy X-ray absorptiometry (DEXA) scan to measure the bone mineral content of the lumbar spine (L1-L4). Disease severity was assessed by lung function and body mass index (BMI) was calculated from weight and height at the time of the DEXA. None of the patients were being treated for low BMD. Random blood samples were analyzed for biochemical markers. The relationship between all these variables and BMD measurements was analyzed. Of 103 patients, ten (9.7%) patients (9 males, 1 female) were diagnosed with osteoporosis. An additional 36 (35%) patients (26 males, 10 females) were identified as having osteopenia. BMI, gender, weight, lung functions (FVC, FEV1, and FEF 25-75), and alkaline phosphatase, and 25-OH vitamin D levels were significantly correlated with Z-scores (p < 0.05). Stepwise linear regression revealed that a low Z-score was best predicted with low FEV1, male gender, low weight, and low 25-OH vitamin D levels (p < 0.05) for each variable. Osteopenia and osteoporosis are common in adults with CF, especially in male patients and in patients with low lung function, body weight, and 25-OH vitamin D levels.