Report evidence, limits, and quality signals

Sweat chloride less than 30 mmol/L is CF unlikely, 30 to 59 mmol/L is intermediate, and 60 mmol/L or greater is consistent with or supports CF under the 2017 CFF guidance. These interpretive categories are age-independent. A single result at or above 60 mmol/L is still not automatic proof that CF is the cause, because other conditions can elevate sweat chloride and confirmation or compatible clinical and genetic evidence is expected.

Monitor QNS performance as a quality signal. CFF and CAP guidance targets roughly below 10 percent QNS in early infancy and below 5 percent for older patients, with sustained higher rates prompting investigation. Proficiency testing for sweat chloride uses simulated liquid human sweat rather than a pilocarpine-collected patient specimen, so it evaluates analytical performance but does not replace collection-quality monitoring.

Keep state algorithm details, collector minimum, analyzer and reagent lot, software, calibration verification, QC acceptance, turnaround time, and report wording in local controlled documents. Release a precise result, name its limits, and never make the clinical diagnosis from one laboratory signal.