Most Adults in CF Study Have Low Bone Mineral Density

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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More than half of adults with cystic fibrosis (CF) who underwent assessments of bone mineral density at a U.S. center had lower-than-expected bone density, a new study reports.

“The prevalence of CF adults with lower than expected BMD [bone mineral density] in this study was found to be more than twice that reported in national registries, suggesting that the actual prevalence in CF adults may be much higher than currently reported,” study researchers wrote.

The results indicate that male sex, older age, poorer lung function, and lower body mass index (BMI) all are risk factors for low bone mineral density among adults with CF.

“While low BMI, low lung function, older age, and male sex were found to be associated with developing lower than expected BMD, individuals without these risk factors were also found to have lower than expected BMD. This supports the importance of universal bone health screening of all CF adults,” the scientists noted.

The study, “Prevalence and Risk Factors for Low Bone Mineral Density in Adults with Cystic Fibrosis,” was published in the journal JBMR Plus.

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People with CF are at heightened risk of bone-related health problems; reduced bone mineral density can lead bones to be weaker and more prone to breaking. Here, scientists at Johns Hopkins University in Maryland, reported data for 234 adults with CF who underwent dual energy X-ray absorptiometry (DXA) scan (a measure of bone mineral density) at their center from 2010 to 2018.

Among the CF patients, 54.1% were female, 93% were white, and the mean age at initial DXA scan was just less than 33. Mean BMI (a ratio of weight to height) was 24.2 kg per square meter (indicating normal weight). More than 80% of the patients had pancreatic insufficiency, while nearly one in three had CF-related diabetes. A little more than half were on a CFTR modulator therapy.

A total of 347 DXA scans were available from the 234 patients. From the total scans, 37.5% indicated normal bone density, while 13.3% indicated CF-related low bone mineral density (CFLBMD). The remaining 47.6% of scans suggested that patients were at risk of CFLBMD, but did not yet definitively have low bone density.

At the initial DXA scan, more than half (52.6%) of the patients had a lower-than-expected bone mineral density. Among patients with more than one DXA scan available, the average time between scans was nearly three years.

There were 25 patients who had normal bone density on the initial scan and had data from subsequent scans available. Among these patients, eight progressed to CFLBMD at later scans, while the other 17 still had normal bone density at later time points.

Among 53 patients deemed at risk of CFLBMD on their initial scan and who had subsequent scans available, six (11.3%) progressed to CFLBMD, nine (17.0%) returned to normal bone density, and the rest were still categorized as at risk of CFLBMD at subsequent assessments.

For 14 patients with an initial scan indicating CFLBMD who had additional scans available, two were returned to a category of at-risk on later scans, while the rest remained categorized as CFLBMD.

Statistical analyses of the available data indicated that male sex and older age were associated with an increased risk of having low bone mineral density. Conversely, patients with high BMI or better lung function scores were generally at lower risk of having reduced bone density.

BMD predictions still tricky

“Although significant associations were found between some analyzed risk factors and lower than expected BMD … individuals with lower than expected BMD have a broad range of clinical characteristics. Therefore, it may not be possible to predict who will develop lower than expected BMD,” the researchers wrote. “These conclusions support the importance of universal bone health screening of all CF adults.”

The researchers pointed out several limitations of this single-center study, including that not all CF patients at their center underwent DXA screening, and that they did not collect data on nutrition and lifestyle factors that likely affect bone mineral density.