Borderline sweat test

Question

My four year old son has low growth issues. His height is 1.03, his weight 15.8 kgr. In height he is in the same percentile consistently, whereas he has dropped from the 75th to the 25th weight percentile.
He has been ill 4 times with a viral infection. He has never taken inhaled medicines and just one antibiotics. In each case he had cough and sputum, and the last time the cough lasted a month with no other symptoms.
We did a general stool test with negative results.
As a newborn we did an IRT test, which came out negative (45.5).
Our paediatrician rules out the possibility for CF and thinks that the low weight is due to the fact that the boy does not eat much.
The blood tests were within normal limits. The only raised value was 13 for eosinophiles. An allergy to milk was detected as well.
The first sweat test was 44, the second 30.5 but we were told that there was not much sweat. They recommended a retest after a month.
I would like to ask what do you think about the possibility of CF?

Answer

Dear friend
Your child has dropped from the 75th weight percentile to the 25th. He presents with viral infections, as most children of his age do. The IRT test after birth was negative and a general stool test was negative as well.
You report that he has allergy to milk and eosinophilia.
There are two sweat tests, one with value 44 mmol/l and another with a value of 30.5 mmol/lt (but with less sweat) and the lab asked for a retest. I would like to inform you that in our lab at the CF center of “Agia Sofia” Hospital the sweat test is conducted with the method of pilocarpine iontophoresis and results over 60mmol/l are considered pathological, according to international and well established clinical guidelines. Results between 40-60 mmol/l are considered to be borderline. Please make sure that the test is performed in an experienced center using the above mentioned method to measure the Chloride concentration in the sweat.
To make a long story short, I do not think that your child has CF and the low growth issue may be attributed to the allergy.
Yours friendly,
Dr. Stavros Doudounakis

25.03.2013