Abnormal Lung Clearance Index in Cystic Fibrosis Screen Positive, Inconclusive Diagnosis (CFSPID) Children with Otherwise Normal FEV1

In preschool children with cystic fibrosis (CF), lung clearance index (LCI) is a sensitive test to detect early lung disease. Some children with CF screen positive, inconclusive diagnosis (CFSPID) may in time develop clinical features of CF. LCI has not been studied in CFSPID children. LCI and spirometry were performed in preschool age children with CF, CFSPID, and non-CF healthy controls (HCs) during two visits. Fifty-four preschool age children (HC n = 18, CFSPID n = 17, and CF n = 19) were tested. Mean LCI from the CFSPID group was not statistically different from HC ( p = 0.49), but significantly different when compared to CF ( p = 0.04). LCI was abnormal in 2 CFSPID children who carried potentially deleterious CFTR variants. Mean forced expiratory volume in 1 s (FEV 1 ) was not statistically different between CFSPID and CF ( p = 0.26). LCI can potentially detect early lung disease in CFSPID individuals as part of assessing their risk for reclassification to CF diagnosis.