Revisiting sweat chloride test results based on recent guidelines for diagnosis of cystic fibrosis

OBJECTIVES: Recent sweat chloride guidelines published by the Cystic Fibrosis Foundation changed the intermediate sweat chloride concentration range from 40–59 mmol/L to 30–59 mmol/L for age > 6 months. We wanted to know how this new guideline would impact detection of cystic fibrosis among patients who previously had sweat tests done at Texas Children's Hospital. METHODS: We revisited sweat chloride test results (n = 3012) in the last 5 years at Texas Children's Hospital based on the new guidelines on diagnosis of cystic fibrosis from the Cystic Fibrosis Foundation. RESULTS: We identified 125 patients that would be reclassified in the intermediate sweat chloride value with the new guidelines that were classified as “unlikely to have CF” in the previous guidelines. 8 (32%) patients with CFTR gene testing were positive for CFTR gene mutation(s). 4 (50%) of these patients were identified to have 2 CFTR mutations. One had variant combination that was reported to cause CF but all were diagnosed with CFTR-related metabolic syndrome. CONCLUSION: Our findings concur with the new CF diagnosis guidelines that changing the intermediate cut-off to 30–59 mmol/L sweat chloride concentration in combination with CFTR genetic analysis enhances the probability of identifying individuals that have risk of developing CF or have CF and enables for earlier therapeutic intervention.