Salivary ribonuclease in cystic fibrosis and control subjects.

Alkaline acid- and thermo-stable ribonuclease (RNAase) was assayed in whole mixed saliva from controls and from cystic fibrosis (CF) heterozygotes and homozygotes. There was a significant difference in salivary RNAase activity between control adults (n = 99) and CF heterozygotes (n = 77) (12.6 +/- 0.60 and 36.6 +/- 2.2 U/l, mean +/- SE respectively; p less than 0.001) and between control children (n = 1834) and CF patients (n = 60) (7.9 +/- 0.15 and 47.0 +/- 5.4 U/l respectively; p less than 0.001). A statistically significant difference in salivary RNAase activity was also found between control children and control adults (p less than 0.001) and between CF homozygotes and CF heterozygotes (p less than 0.001). The protein concentration was significantly increased by about 50-60% in saliva both from CF heterozygotes and from CF homozygotes (p less than 0.001 for both groups). It is concluded that in view of the great overlapping in values between the groups, these tests can only be of limited use for diagnostic purposes.