Bilateral sweat tests with two different methods as a part of cystic fibrosis newborn screening (CF NBS) protocol and additional quality control

Infants with positive CF newborn screening (NBS) results are called to a CF Centre for verification. Those, in whom the sweat test is elevated, undergo further medical procedures. The aim of our study was to evaluate the applicability of Nanoduct - a new system measuring sweat conductivity and giving immediate results in a CF NBS protocol. Measurements with Nanoduct were compared with the classic pilocarpine method. During 3 years 487 infants from CF NBS had both sweat tests performed on the same day, at the same CF centre. CF infants had a mean conductivity of 99.8+/-18.8 mmol/L and a mean chloride concentration of 74.0+/-18.4 mmol/L. Non-CF infants values were 29.8+/-7.7mmol/L and 19.2+/-6.6 mmol/L respectively. A good correlation between both tests was found (95% confidence level (CI); r=0.87). The optimal cut off, based on follow up experience of screened children, for conductivity tests was 50 mmol/L and for chloride concentration was 34 mmol/L (no lost CF, 11 false positive) with 100% sensitivity and 97.5 % specificity. In conclusion Nanoduct is a very useful and reliable tool in CF NBS protocol, allowing more time efficient organization of the diagnostic and training procedures. Simultaneous bilateral sweat testing with two different methods (concentration and conductivity) provides an extra quality control system.