Association of sweat chloride concentration at time of diagnosis and CFTR genotype with mortality and cystic fibrosis phenotype

BackgroundThe extent to which sweat chloride concentration predicts survival and clinical phenotype independently of CFTR genotype in cystic fibrosis is not well understood.MethodsWe analyzed the US Cystic Fibrosis Foundation Patient Registry data using Cox regression to examine the relationship between sweat chloride concentration (< 60, 60–< 80, ≥ 80 mmol/L), CFTR genotype (high and lower risk for lung function decline), and survival and mixed linear regression to examine the relationship between sweat chloride, CFTR genotype, and measures of lung function and growth.ResultsWhen included in the same model, CFTR genotype, but not sweat chloride, was independently associated with survival and with lung function, height, and BMI. Among patients with unclassified CFTR genotype, sweat chloride was an independent predictor of survival (< 60 HR 0.53 [0.37, 0.77], 60–< 80 0.51 [0.42, 0.63]).ConclusionsSweat chloride concentration may be a useful predictor of mortality and clinical phenotype when CFTR genotype functional class is unclassified.