The problem with this approach is that there are nearly 400 different variations of the CF gene, not all of which can be identified by DNA analysis. Genetic testing Pulmonary Function Test Back to Top Prenatal Diagnosis Prenatal genetic testing can be used to determine whether an unborn baby has CF, although the testing is not foolproof, many of the nearly 400 different mutations that can lead to CF cannot be detected. Because prenatal genetic testing is expensive and carries some risk to the mother, not all women who are CF carriers choose to have the tests done.
Prenatal testing involves either amniocentesis or a chorionic villus biopsy.
In the former, cells are removed from the amniotic fluid the fluid that surrounds the fetus. A chorionic villus biopsy involves sampling tissue that develops into the placenta. Because CF is an inherited disorder, any family history of CF suggests that the gene is present in the lineage. Many adults who do not have CF have a fairly high Cl- level in their blood. A very small percentage of CF patients have normal salt levels in their sweat, in which case they have to be genetically tested to determine the presence of the defective gene.