False negative sweat tests with apparently adequate sweat collections.

Sweat tests collected on two or more occasions from normal children and 
children with cystic fibrosis have been analysed according to the weight 
of sweat collected. In five cases collections of 50-99 mg of 
sweat gave false negative results. Although 50-100 mg of sweat is 
considered adequate by some authorities our results do not support this. 
The study confirms the view that at least 100 mg of 
sweat must be collected to give reliable results. 