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. 