Sweat chlorides

Question

Hello, I would like to ask about the factors which could influence the chloride measurements in CF. My child had the chloride test twice because we had to go to the hospital twice for pneumonia, and the results were 37 and the second was 47. He has no symptoms; even the second pneumonia was due to the fact that the first one was not treated properly. He is two months old, is very lively, eats well, and does not taste salty. We will go to Bratislava for a repeat of the tests. Could he have CF despite all this? What are the factors that influence this test? Thank you

Answer

Hello.
1. The test should be done by a laboratory with sufficient experience, which means that it should carry out at least 250 tests per year.
2. It is very important to get a sufficient amount of sweat, which means at least 100 mg.
3. The child should be well-hydrated; they should not have a fever when being tested.
If the first two tests fulfilled these criteria and if a borderline sweat test value is shown again, molecular genetic tests should be performed. Only the finding of two genetic mutations for CF can confirm the diagnosis. It is very probable that one of these mutations belongs to the so-called mild ones, because the results you mentioned are borderline; they do not exceed a value of 60 mmol/l, which would indicate CF. This occurs in people with CF with a "serious" mutation in the CFTR gene together with expressions of pancreatic insufficiency.
An increased level of chloride exists in the sweat in other diseases as well.
Additional factors which may influence the results are not yet known, and there have been considerations about the relationship between certain anti-epileptic medications and increased chloride levels in the sweat.

Best regards, Vera Vavrova and Jitka Brazova

29.04.2009