The airflow in the first second of forced expiration (FEV1) and body mass index (BMI) are well-validated predictors of disease severity and outcome in Cystic Fibrosis (CF), however, the impact of sex upon these remains debated. The UKCF Registry features demographic and clinical information on >99% of the UKCF population (~10,000 individuals). Data were used to investigate the sex difference in change in FEV1 or BMI between 2008-2013, and if this difference could be explained by chronic

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... nas aeruginosa (cPsA) infection or CFrelated diabetes (CFRD). Longitudinal analyses (2008-2013) compared male/female age at cPsA acquisition as well as FEV1 and BMI differences between individuals with cPsA. Regression analysis examined for a difference in change in BMI and FEV1 between the sexes depending on CFRD and cPsA status, adjusting for age, genotype and ethnicity. Survival analysis completed the analysis. Females were significantly younger than males at the time of new cPsA infection (20.9 vs 22.4years; p<0.001) with a lower mean BMI with new cPsA (21.3 vs 22.2years;p<0.001) but no difference in FEV1 at time of new cPsA. Females had greater decline in FEV1 than males (8.2% vs 7.0%; p<0.001), this was even greater in individuals with cPsA (10.2% vs 8.2% in males:p=0.002). Females had less of an increase in BMI than males (0.2 vs 0.6 in males;p<0.001), this difference was only seen in individuals with cPsA. Sex differences in change in BMI were also seen with CFRD. Overall, median survival for females was significantly less than males (42.3 vs 48.0 years,p<0.001). Females with CFRD had the worst survival overall. These data suggest a measurable sex difference in clinically relevant CF outcomes in the UK population. Consequently there might be scope for research 4 into clinical interventions to try and remove such sex differences, by potentially focusing upon PsA infection, CFRD or sex hormone manipulation.