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 interpretati on. Methods-Questionnaire responses from 30 self selected centres: 15 paediatri c centres, and 15 district general hospitals. Results-Centres carried out 30-400 tests per year (median 100), with a diag nostic 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 sweat ing by pilocarpine iontophoresis using varying currents and times. Twenty s ix had observed urticaria or skin reddening, and nine blistering or burns. Sweat was collected for 10-60 minutes onto filter paper or into Macroduct c oils. Between 2% and 25% of tests were considered insufficient. Twenty eigh t measured sodium, 24 chloride, and one osmolality and conductivity. Fiftee n 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 na tional guideline to standardise collection, and external quality assessment to provide analytical feedback.