These thresholds are thought to be clinically significant because health-care providers use them in their diagnosis of cystic fibrosis and data from both natural history and pooled clinical trials suggest that people with cystic fibrosis with sweat chloride concentrations of less than 60 mmol/L and 30 mmol/L have better clinical outcomes than do those with cystic fibrosis and sweat chloride concentration of 60 mmol/L or higher;20,21 however, these sweat chloride thresholds have not yet been used prospectively to evaluate response of CFTR modulator therapy. The gene discussed is CFTR; the disease is cystic fibrosis.