possibility for CF

Question

One of my twin boys, born 28 weeks, with low-birth weight (1,49 kg but now 9.2 kg at 32 months of age) had a sweat test with sweat volume 16K and result 59 The sweat test was done with the method of iontophoresis of pilocarpine at Rio. We could not perform another test, because the child does not sweat.
During his first year of life he did not get sick. In his second year he had 4 episodes of bronchitis and this year 3 already. He is a hyperactive kid that eats a little and gains little weight. His bowel movements are 1-2 a day and do not float. The gastroenterologist (we visit him due to the low growth issue) and the pneumonologist have excluded the possibility of Cystic Fibrosis, but what about the sweat test and the episodes of bronchitis? The child has been genetically tested for the most common mutation in Greece (95%) at Horemio lab and myself for the 75% of the mutations with negative results. My husband has not been tested. The last blood tests in May were good. What do you think I should do? What are the chances of my son having CF?
My doctors insist that the child does not have CF, not even the clinical symptoms of CF, but the combination of low weight - frequent bronchitis and the value of 59 at the sweat test do not let me rest. Is there something else I can do?

Answer

Dear friend,
The value of the sweat test you keep bringing up (59) seems to be within normal limits, as stated by the lab that performed it (0-60 normal, 60-80 borderline, >80 pathological). However, it has to be stated, that if the test is performed in a standardized way and the pilocarpine ionotophoresis was used to measure the chloride concentration in the sweat, the following standardized reference values pertain: chloride concentration 0-40 mmol/l normal, 40-60mmol/l borderline and over 60 mmol/l pathological. Therefore, the used reference values of the lab are striking and we cannot judge the reliability of the performed test. It would therefore be recommendable to do another sweat test at our lab in order for you to quench your doubts about the possibility of CF. Our lab does a very large number of such tests annually and the personnel is very experienced.
Your child has undergone the genetic analysis for a very large number of CF mutations (95%), which was negative, so the chances are really low that your child suffers from CF. If the sweat test will reliably be negative and the child does not present symptoms of CF, one must look elsewhere for the bronchitis and low weight issues, since there are many causes (e.g. asthma, gastroeophageal reflux) that could be responsible.
You can contact the lab for an appointment [Telephone number was given]. If I am not present, leave a message with your details and I will contact you.
Yours friendly,
Dr. Stavros Doudounakis and Dr. Daniela d'Alquen

19.07.2012