Sweat test in case of atopic eczema

Question

Recently, a sweat test has been performed to my son (2.5 years old)...because of suspicion of CF...result was 45mmol/l...he also has severe atopic eczema, I have read that in case of atopic eczema the value can also be wrong....have great fear and I am totally insecure...Therefore my question, if it would make sense to do another test???

Answer

Hello,

You report, that a sweat test has been performed to your son (age: 2.5 years) because of suspicion of CF and that a value of 45 mmol/l chloride has been measured. As your son suffers from atopic eczema and you have read that in case of atopic eczema the values could be wrong, you are very worried and ask, if one should not do a test again to be on the safe side.
First of all it has to be emphazised that in case of atopic eczema, a sweat test could be wrongly increased, in case the test has been performed at a region of the skin that is affected by the atopic eczema. The result of your son is in the upper borderline area of the normal range respectively there are very occasionally patients with CF who show a value of 45 mmol/l. The test result speaks therefore with a certain security against the illness of CF. However, it could of course be the case, that the value is in this region, because the test of your son has been performed on an arm affected by the atopic eczema. I would therefore recommend, that you talk to your physician about your worries and ask him to arrange the performance of another test. This test should then in any case be performed at a CF-center, that is experienced in the performance of a sweat test to patients with skin problems. Often it makes sense, to do the test at the back in children with atopic eczema, as this region of the body is often not as severly affected by the atopic eczema.

We wish you much luck and hope that a new result can take your fears away.
Yours sincerely,
Dr. H.-G. Posselt

19.08.2013