Edema as the presenting symptom of cystic fibrosis: difficulties in diagnosis.

Hypoproteinemia and edema may develop in infants with cystic fibrosis whatever their 
diet although prior ingestion of soy bean formula appears to be 
a predisposing factor, and a negative sweat chloride test may be 
present in a CF child during the hypoproteinemic phase of the 
illness. The diagnosis cannot be excluded until a negative test with 
adequate secretion of sweat is obtained after edema and hypoproteinemia have 
resolved. 