Hemoglobin Levels in Children Treated for Cystic Fibrosis with CFTR Modulators: A Single Center Retrospective Study

Background: An increase in hemoglobin (Hb) has been reported in subjects with CF treated with the CFTR modulator Ivacaftor and with the combination Lumacaftor/Ivacaftor (LI), while the literature about the impact of Elexacaftor/Tezacaftor/Ivacaftor (ETI) on Hb levels in the pediatric population is lacking. Materials and Methods: We retrospectively evaluated Hb levels in 35 subjects with CF (18 males, median age: 8 years; interquartile range (IQR): 6-13 years) treated with LI and 60 (24 males, median age: 10 years; IQR: 6-14 years) treated with ETI. For each subject we considered the values of Hb, serum potassium, total bilirubin (TB), and conjugated bilirubin (CB) at baseline, after 3 days, and 1, 3, 6, 9, and 12 months from the start of treatment. Results: In subjects with CF treated with LI, we observed a significant increase in Hb values 3 days after the introduction of the drug, which remained constant throughout the year of treatment. In subjects treated with ETI, a significant decrease in Hb was observed 3 days after the first dose up to 1 month. At 6 months, Hb returned to pre-treatment values remaining stable for up to 12 months. At 3 days of treatment, we also observed a significant increase in serum potassium, which returned to normal at one month, while both TB and CB values significantly increased at 3 days of treatment and remained significantly higher for the whole one-year period of ETI therapy. Conclusions: We confirmed an increase in Hb values over time in subjects treated with LI. While the Hb response in those treated with ETI showed a transient reduction that lasted for one month, this may have depended on hemolysis, and returned to pre-treatment levels. Further studies will clarify the mechanisms that govern changes in Hb in subjects with CF treated with ETI.