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.