GSTM1 and cystic fibrosis: 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.