Image-based β-adrenergic sweat rate assay captures minimal cystic fibrosis transmembrane conductance regulator function.

There is a need to prognosticate the severity of cystic fibrosis (CF) detected by newborn screening (NBS) by early assessment of CF transmembrane conductance regulator (CFTR) protein function. We introduce novel instrumentation and protocol for evaluating CFTR activity as reflected by β-adrenergically stimulated sweat secretion. A pixilated image sensor detects sweat rates. Compounds necessary for maximum sweat gland stimulation are applied by iontophoresis, replacing ID injections. Results are compared to a validated β-adrenergic assay that measures sweat secretion by evaporation (evaporimetry). Ten healthy controls (HC), 6 heterozygous (carriers), 5 with CFTR-related metabolic syndrome (CRMS)/CF screen-positive, inconclusive diagnosis (CFSPID), and 12 CF individuals completed testing. All individuals with minimal and residual function CFTR mutations had low ratios of β-adrenergically stimulated sweat rate to cholinergically stimulated sweat rate (β/chol) as measured by either assay. β-Adrenergic assays quantitate CFTR dysfunction in the secretory pathway of sweat glands in CF and CRMS/CFSPID populations. This novel image-sensor and iontophoresis protocol detect CFTR function with minimal and residual function and is a feasible test for young children because it is insensible to movement and it decreases the number of injections. It may also assist to distinguish between CF and CRMS/CFSPID diagnosis.