Research Article

Sweat tests to diagnose cystic fibrosis in adults.

Br Med J (Clin Res Ed) 1983; 286 doi: (Published 30 April 1983) Cite this as: Br Med J (Clin Res Ed) 1983;286:1381
  1. M E Hodson,
  2. I Beldon,
  3. R Power,
  4. F R Duncan,
  5. M Bamber,
  6. J C Batten


    Twenty five patients with cystic fibrosis and 25 controls were studied to define a sweat sodium concentration in adults that could be taken as diagnostic of cystic fibrosis. Some of the controls had a sweat sodium concentration of over 50 mmol(mEq)/l, and thus cystic fibrosis should be diagnosed in an adult only when two measurements of sweat sodium concentration are above 70 mmol/l. In cases in which the sweat sodium concentration was borderline a suppression test using fludrocortisone improved the accuracy of diagnosis; this test entails recording the lowest concentration reached after administration of the drug. A scatter diagram of the baseline sweat sodium concentrations plotted against the lowest concentration attained after suppression with fludrocortisone may aid the diagnosis further.