β-Adrenergic Sweat Secretion as a Diagnostic Test for Cystic Fibrosis

Rationale beta-Adrenergically induced sweat secretion offers an expedient method to assess native cystic fibrosis transmembrane conductance regulator (CFTR) secretory function in vivo. Objectives: To evaluate the sensitivity, specificity, and reliability of a test based on the activity and secretory function of CFTR in the sweat gland. Methods: Primary and validation trials with prospectively ascertained healthy control subjects, obligate heterozygotes, and patients with a CFTR-related disorder and CF (pancreatic sufficient and insufficient). Measurements and Main Results: Diagnostic accuracy and reliability of beta-adrenergic sweat secretory rates using an evaporimeter was assessed and compared with sweat chloride concentrations. The cholinergically stimulated mean sweat rate did not differ among groups. The mean maximal beta-adrenergically stimulated sweat rate in heterozygotes was about half the rate of healthy control subjects, and completely absent in pancreatic-insufficient patients with CF and pancreatic-sufficient patients with CF (P < 0.0001). Subjects with a CFTR-related disorder showed reduced or absent beta-adrenergic sweat secretion. The beta-adrenergic secretory response demonstrated high diagnostic accuracy (area under a characteristic receiver-operator curve = 0.99; 95% confidence interval, 0.97-1.00) and reliability (intraclass correlation, 0.90; 95% confidence interval, 0.81-0.95). The diagnostic cutoff level for CF, derived from the primary trial, correctly identified all control subjects, heterozygotes, and patients with CF in the validation cohort, whereas concurrent sweat chloride measurements misclassified one heterozygote and five subjects with CF. The cholinergic and beta-adrenergic sweat secretion rates were lower in women compared with men (P < 0.001). Conclusions: beta-Adrenergic sweat secretion rate determined by evaporimetry is an accurate and reliable technique to assess different levels of CFTR function and to identify patients with CF.