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Sweat test

Question
Hello,
my daughter has had a sweat test in a CF center. I have been told, that for diagnosis only the chloride value was important, this could however take some time. As I am a worrying mum of a perterm baby, one could see my fear and I got the information that the conductivity was about 35 mmol/l. Can I relax a bit or is it possible to have the combination: normal conductivity but pathological chloride?
Many thanks for your efforts
Answer
Hello,
you report, that your daughter has had a sweat test with the conductivity method in a CF center and that a value of 35 mmol had been the result. You have been told, that for a secure diagnosis, the measurement of chloride via a chloridometer would be necessary. This test can seemingly not be performed in a short time interval. Therefore your are worrying and ask, if the value of 35 would be calming or if it could be, that the chloride measurement could never the less be pathological.
If I got you right, your daughter is a former preterm baby. As I do not know, which symptoms have caused the suspicion for CF, I assume, that there are some lung problems which could also be due to the preterm birth. The value of 35 mmol/l is in the lower area of the grey zone and to be secure, a sweat test with measurement of the chloride concentration should be done. Therefore, most centers only do the chloride measurement. Unfortunately, it is like this, that the results of both test could be very differing. A real relief could here only be achieved via a quick control investigation. If the CF center cannot give you an appointment in a short time interval, please get the name of another center, that is next to your home, that could provide a quicker appointment.
Best regards,
Dr. H.-G. Posselt
19.05.2017