Inconsistencies in sweat testing in UK laboratories

Background-Sweat testing procedures are perceived to vary widely. Aim-To evaluate variability in sweat collection, analysis, and interpretation. Methods-Questionnaire responses from 30 self selected centres: 15 paediatric centres, and 15 district general hospitals. Results-Centres carried out 30-400 tests per year (median 100), with a diagnostic rate of 1:5-152 (median 1:30). Staff performed 5-268 tests per year. Minimum test age varied from 24 hours to four months. All stimulated sweating by pilocarpine iontophoresis using varying currents and times. Twenty six had observed urticaria or skin reddening, and nine blistering or burns. Sweat was collected for 10-60 minutes onto filter paper or into Macroduct coils. Between 2% and 25% of tests were considered insufficient. Twenty eight measured sodium, 24 chloride, and one osmolality and conductivity. Fifteen used literature and five in house reference ranges. Eleven would not test severely eczematous children. Conclusions-Local audit is required to improve performance, as well as a national guideline to standardise collection, and external quality assessment to provide analytical feedback.