Sweat test borderline?

Question

Hello,
yesterday we have been with our daughter at a center spezialized in pulmonology, as asthma was suspected. However, as she has again and again vomited mucus in the mornings, they performed a sweat test.
The value was 52 mval/l. The physician said, the value was normal, however our pediatrician said, it was borderline and recommends another sweat test.
What is true now? What do you recommend?
She is healthy, does not take drugs and the sweat has been collected for about 30 minutes.
Best regards,

Answer

Hello,
you report, that a sweat test had been performed to your daughter at a spezialized center for pulmonology in case of suspected asthma, that showed a value of 52 mval/L. There you have been told, the value was normal while your pediatrician pointed out the value was borderline and recommended a control.
Here it has to be said clearly, that your pediatrician is right. In case of such a result, the sweat test should at first be repeated with a double measurement at both arms. For this, you should visit a CF center, in case the first investigation had not already been performed at such a center. In case it would come out then, that the new values are in the same range, ongoing diagnostics is necessary, that should then be discussed with the CF experts.

Best regards,
Dr. H.-G. Posselt

28.02.2014

28.2.14

It is important to know whether the sweat test has been performed at an experienced center using the so-called “pilocarpine ionotophoresis” method to measure the chloride concentration in the sweat. Only if this is the case the result mentioned of 52 mval/l (we have to assume that this is the chloride concentration) can be interpreted according to standardized values.
Chloride concentrations in the sweat greater than or equal to 60mmol/l are considered consistent with the diagnosis of CF. If the result is 40-59mmol/l chloride concentration in the sweat, it is in the borderline area and the test should be repeated; as mentioned above, if the result is then still borderline, ongoing investigations can help clarifying the situation. Values of less than 40mmol/l chloride concentration are considered to be negative.
D. d'Alquen