Doubtful sweat tests

Question

I have two daughters, 4 and 6 years old. Both are carriers of the W1282X CF, mutation, as I am, whilst my husband is negative. Their health in general is good. The values of their sweat tests are borderline. The older one has been tested 3 times (values 25.2-55.5-38.3), and the younger one twice (values 42.1-55.9).
I am really worried and I do not know if I must have them tested in some other way. Could these elevated values be attributed to them being carrriers?

Answer

Dear friend,
Before I try to answer your question I would really like to know the following:
a. Why were you tested for CF mutations, after which you were found to carry the mutation W1282X?
b. Where were the sweat tests performed and which method was used (or were there different methods used?) As the values can only be interpreted by us or used as a vaild tool if the test was performed in an experienced center and measured the Chloride concentration of the sweat with pilocaprine ionotophoresis.
c. How many mutations were your husband and daughters tested for?

In any case your older daughter, for whom three sweat tests were performed, has two normal result values (assumed that they were measured as described above) and one intermediate value and, clinically speaking, in general she is fine. Based on the above I do not think she has something, but simply is a carrier of a CF mutation.
Your younger daughter, who had two sweat tests, has two intermediate result values and in general is quite well without any symptoms. In her case I recommend to have one more sweat test performed, as well as a comprehensive genotype testing, if it has not already been done, since it is quite possible that your younger daughter is a carrier of a CF mutation, or has an atypical, mild form of the disease.
Yours friendly,
Dr. Stavros Doudounakis

04.10.2011