Cystic fibrosis screening by sweat analysis: a critical review of techniques.

Currently employed methods for the assay of electrolytes in sweat, relevant to 
the diagnosis of cystic fibrosis, are critically evaluated with particular reference 
to the measurement of electrical conductivity. Attention is drawn to the 
factors responsible for potentially large errors. On the basis of experimentation, 
supported by laboratory practice, recommendations are made for the reduction of 
these errors to clinically acceptable levels. Data concerning sodium and potassium 
content, electrical conductivity and osmolality of undiluted sweat collections are compared. 
The feasibility and comparative advantages of measuring sweat osmolality with a 
vapour pressure osmometer are discussed. 