For the CFTR-specific PLx assay, positive signal intensities varied between 2000 and 5000 MFI and background signal varied from 50 to 1500 MFI. The variation in signal depended strictly on the target sequence. We observed that determination windows varied from 0.99 to 0.7 for wild-type samples, from 0.4 to 0.6 for heterozygous samples, and from 0.0 to 0.2 for homozygous mutant samples.