Sweat testing practices in German cystic fibrosis centres

Background: Surveys in USA and UK have shown inconsistencies between practice of sweat testing and guidelines of the National Committee for Clinical Laboratory Standards (NCCLS), which could increase the risk of false-positive and -negative results. To determine the current practice of sweat testing in German cystic fibrosis (CF)centres a survey was performed. Method: A questionnaire was mailed to all 123 German CF-centres that join the German CF-register. The results were compared with the NCCLS-guidelines. Results: 88 out of 113 responding centres perform 30-1100 (median 200) sweat tests by pilocarpine iontophoresis per year. The recommended sweat sample time of 20-30min was accepted by 33% of all centres. Minimum acceptable sweat rates were quoted between 100 and 7500 (median 1000) mg/m(2)/min differing from the recommended 1000mg/m(2)/min. Osmolality was measured in 3%, sodium in 24% and conductivity in 53% of the centres. Chloride, the only accepted diagnostic measurement by the NCCLS, was investigated by only 58% of all centres. The recommended chloride CF-reference value of > 60 mmol/l was used in 78% of centres that perform chloride testing. Conclusions: Major areas of inconsistencies between sweat testing practice in German CF-centres and NCCLS-guidelines are sweat collection, analyzing method and reference values. Chloride, the only accepted diagnostic measurement by the NCCLS, was investigated only by 58% of all centres.