Sweat test below 10 however symptoms in spite of this

Question

Hello,
We are parents of a 2-year-old boy. He has not really gained weight since he was one year old and has eaten not well. We found it striking, that his head tasted very salty and that he had bowel movements very often. A sweat test had been negative (not even in the borderline range) and we were told not to worry anymore.
Now a vitamin A deficiency has been diagnosed and as we informed ourselves, this does i.a. occur in case of CF. As we nourish our child rather healthy and balanced (much vitamin A containing vegetables including oil) we cannot explain this.
Furthermore, he has had recently recurrent airway infections, that we could handle well with herbal drugs and inhalation via pariboy.
What else can we do in order to have real security that he is suffering from CF or not?

Answer

Hello,
you report, that your 2-year-old boy did not really gain weight since he was one year old and that the appetite has got worse. You report furthermore, that his sweat would be very salty and that he is quite frequently having bowel movements. A sweat test had been normal (below 10 mval/l chloride?). As he also has had some airway infections and because a vitamin A deficiency has been diagnosed, you worry and ask how the illness of CF can be excluded with 100% security. First of all, I have to ask, if the sweat test had been done at a certified CF Center. As a value below 10 mval/l for chloride is very seldom in healthy people, I would propose, that as a first step the sweat test should be repeated on both arms at a certified CF Center. If the results should be the same as with the first test, one can assume with great security, that no CF is underlying.
In cooperation with a pediatric gastro-enterology department, a stool investigation of pancreatic elastase I should be done because of the vitamin A deficiency, in oder to clarify, if the pancreatic function of your son is o.k. Besides the illness of CF, there are other rare diseases, that are going along with pancreatic insufficiency. If the value for the elastase I is normal, an intolerace for gluten (celiac disease) has to be excluded. Also with this illness, a deficiency of fat soluble vitamins can occur.
I wish you and your son all the best,
Best regards,
Dr. H.-g. Posselt

02.04.2015