Background: Infants with a positive cystic fibrosis (CF) newborn screen, only one identified CFTR mutation (NBS+/1 mut), and an initial intermediate sweat chloride (30-59 mmol/L) should have repeat sweat chloride testing (SCT). However, the outcome of repeat SCT and the relationship between initial sweat Cl and subsequent CF diagnosis have not been reported.
Objective: The objective of this study was to analyze the outcomes of repeat SCT and subsequent CF diagnosis in NBS+/1 mut infants based on their initial sweat chloride concentration.
Methods: We retrospectively identified all infants born in Indiana from 2007 to 2017 with NBS+/1 mut and initial SCT in the intermediate range. For each infant, we recorded the initial and repeat SCT results and/or a final CF diagnosis.
Results: From 2007 through 2017 there were 2822 NBS+/1 mut infants of which 2613 (82%) had at least one SCT result. No infants with an initial SCT of 30-39 mmol/L were subsequently diagnosed with CF. Of the 31 infants with an initial SCT of 40-49 mmol/L, only 1 was subsequently diagnosed with CF. In contrast, 61% of those with SCTs of 50-59 mmol/L were later diagnosed with CF.
Conclusion: These results suggest that infants with a positive NBS for CF and one CFTR mutationwhose initial sweat chloride concentration is 50-59 mmol/L need to be monitored more closely forCF with strong consideration for earlier repeat SCTs and immediate genotyping.
Keywords: CFTR; genetics; laboratory medicine.
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