Letter: Cystic fibrosis with edema and falsely negative sweat test.

The recent interesting report on cystic fibrosis with edema and falsely negative 
sweat test prompted us to report a similar case. The previously 
reported similar cases and this one suggest that when cystic fibrosis 
is suspected in an edematous infant and the sweat chloride or 
sodium concentration is within the normal range, the test should be 
repeated after the edema has disappeared. 