Gradual increase in sweat chloride concentration is associated with a higher risk of CRMS/CFSPID to CF reclassification

• Published in: Pediatric pulmonology 2023-04, Vol.58 (4), p.1074-1084
• Main Authors: Salinas, Danieli B., Ginsburg, Daniella K., Wee, Choo Phei, Saeed, Muhammed M., Brewington, John J.
• Format: Article
• Language: English
• Subjects: CFSPID; Child; Chlorides; CRMS; Cross-Sectional Studies; Cystic fibrosis; Cystic Fibrosis - diagnosis; Cystic Fibrosis - genetics; Cystic Fibrosis Transmembrane Conductance Regulator - genetics; Humans; Infant; Infant, Newborn; Medical screening; Neonatal Screening; newborn screening; Retrospective Studies; Sweat; Trypsinogen
• ISSN: 8755-6863; 1099-0496
• DOI: 10.1002/ppul.26296

Objectives Universal implementation of cystic fibrosis (CF) newborn screening (NBS) has led to the diagnostic dilemma of infants with CF screen‐positive, inconclusive diagnosis (CFSPID), with limited guidance regarding prognosis and standardized care. Rates of reclassification from CFSPID to CF vary and risk factors for reclassification are not well established. We investigated whether clinical characteristics are associated with the risk of reclassification from CFSPID to a CF diagnosis. Methods Children with a positive CF NBS were recruited from two sites in California. Retrospective, longitudinal, and cross‐sectional data were collected. A subset of subjects had nasal epithelial cells collected for CF transmembrane conductance regulator (CFTR) functional assessment. Multivariate logistic regression was used to assess the risk of reclassification. Results A total of 112 children completed the study (CF = 53, CFSPID = 59). Phenotypic characteristics between groups showed differences in pancreatic insufficiency prevalence, immunoreactive trypsinogen (IRT) levels, and Pseudomonas aeruginosa (PSA) colonization. Spirometry measures were not different between groups. Nasal epithelial cells from 10 subjects showed 7%–30% of wild‐type (WT)‐CFTR (wtCFTR) function in those who reclassified and 27%–67% of wtCFTR function in those who retained the CFSPID designation. Modeling revealed that increasing sweat chloride concentration (sw[Cl−]) and PSA colonization were independent risk factors for reclassification to CF. Conclusion Increasing sw[Cl−] and a history of PSA colonization are associated with the risk of reclassification from CFSPID to CF in a population with high IRT and two CFTR variants. A close follow‐up to monitor phenotypic changes remains critical in this population. The role of CFTR functional assays in this population requires further exploration.