Detection of cystic fibrosis heterozygotes using a modified loading with bromide.

A three day loading with sodium bromide was performed in 19 healthy controls, 16 definite cystic fibrosis heterozygotes, and 14 homozygote patients with cystic fibrosis. After three days sodium, potassium, chloride, and bromide were determined in serum and sweat. Using a multivariate discriminant analysis two nonelementary functions with the features sodium index, bromide index, potassium index, and chloride in sweat allowed us to identify the three groups. The reclassification of the probands, however, was correct in only 69.3%. A second analysis with the groups of controls and heterozygotes only resulted in a unidimensional nonelementary function with the features potassium index, bromide/sodium in sweat, and sodium index. The reclassification of the probands was correct in 91.4%. The discriminant values were 8.28 +/- 0.96 in the controls and 11.67 +/- 1.03 in the heterozygotes with an overlap of twice the standard deviations between 9.61 and 10.20.