Impact of triple Cystic Fibrosis Transmembrane regulator (CFTR) modulator on bone density in Cystic Fibrosis (CF): a retrospective cohort analysis

<bold>Background:</bold> The triple CFTR modulator therapy elexacaftor/tezacaftor/ivacaftor (ETI) has been available for eligible patients with CF aged 12+ years since August 2020 in the UK. The benefits of ETI on pulmonary function has been well demonstrated, however the effect on bone density is not well characterised. <bold>Aims and Objectives:</bold> Assessment of the bone density of our patient cohort between 2019 and 2023, before and after starting ETI. <bold>Methods:</bold> Cohort of 97 patients, 47 female and 50 male. Identification of patient T-scores from most recent DEXA scans prior to, and after starting, ETI. Collection of data on vitamin D levels, bisphosphonate use and body mass index (BMI) before and after starting ETI. Assessment of statistical significance using paired T-test and Chi squared test. <bold>Results:</bold> No significant change in bone density as measured by T scores after starting ETI. Average lumbar spine density decreased by 0.03 SD, and average hip density decreased by 0.09 SD. There was a non-significant reduction in number of osteoporotic patients after introduction of ETI (11 versus 8 patients), and a non-significant increase in number of osteopenic patients (43 versus 47 patients). There was a non-significant decrease in average vitamin D levels of -0.4nmol/L, but a significant increase in average BMI of 1.3 (p<0.001). <bold>Conclusions:</bold> There was no significant change in bone density in our cohort after starting ETI over the average time period of 2.1 years. More work is required to understand and assess the long term impact of CFTR modulators on bone health in the CF population.