Reliable diagnosis of the major type of cystic fibrosis with fibroblast cultures. A double blind study.

A double blind study has been carried out to demonstrate that the most common type of cystic fibrosis (CF) can be reliably diagnosed with skin-derived fibroblast cultures. Alkaline phosphatase (AIP) activity has been measured in 6 normal controls, 12 CF-heterozygotes and 6 CF-homozygotes before and after stimulation with Tamm-Horsfall-glycoprotein (THP), isoproterenol and theophyline ("THP-induction test"). The mean AIP-activities after THP-induction were 8.8, 12.7 and 34.6 for the three different genotypes respectively. There was no overlap between the values of CF-homozygotes on the one hand, and the values of CF-heterozygotes and normal controls on the other hand. All 24 specimens were correctly diagnosed in the present double blind study, indicating the very high degree of reliability of the THP-induction test in the detection of the predominant type of cystic fibrosis with fibroblast cultures. Normal controls and CF-heterozygotes could not be discriminated on an individual basis, but as a group the CF-heterozygotes displayed higher AIP-values.