Association between CFTR modulators and changes in iron deficiency markers in cystic fibrosis

Background Iron deficiency (ID) is a common extrapulmonary manifestation in cystic fibrosis (CF). CF transmembrane conductance regulator (CFTR) modulator therapies, particularly highly-effective modulator therapy (HEMT), have drastically improved health status in a majority of people with CF. We hypothesize that CFTR modulator use is associated with improved markers of ID. Methods In a multicenter retrospective cohort study across 4 United States CF centers 2012–2022, the association between modulator therapies and ID laboratory outcomes was estimated using multivariable linear mixed effects models overall and by key subgroups. Summary statistics describe the prevalence and trends of ID, defined a priori as transferrin saturation (TSAT) <20 % or serum iron <60 μg/dL (<10.7 μmol/L). Results A total of 568 patients with 2571 person-years of follow-up were included in analyses. Compared to off modulator therapy, HEMT was associated with +8.4 % TSAT (95 % confidence interval [CI], +6.3–10.6 %; p < 0.0001) and +34.4 μg/dL serum iron (95 % CI, +26.7–42.1 μg/dL; p < 0.0001) overall; +5.4 % TSAT (95 % CI, +2.8–8.0 %; p = 0.0001) and +22.1 μg/dL serum iron (95 % CI, +13.5–30.8 μg/dL; p < 0.0001) in females; and +11.4 % TSAT (95 % CI, +7.9–14.8 %; p < 0.0001) and +46.0 μg/dL serum iron (95 % CI, +33.3–58.8 μg/dL; p < 0.0001) in males. Ferritin was not different in those taking modulator therapy relative to off modulator therapy. Hemoglobin was overall higher with use of modulator therapy. The prevalence of ID was high throughout the study period (32.8 % in those treated with HEMT). Conclusions ID remains a prevalent comorbidity in CF, despite availability of HEMT. Modulator use, particularly of HEMT, is associated with improved markers for ID (TSAT, serum iron) and anemia (hemoglobin).