transpiration result

Question

My child (2 years 5 months) had a sweat test result; the result was 46 ... so we found about this disease.
I learned that the test should be repeated to know for sure ...

The question is: if 2 days before the test the child was about two days infusion of NaCl (+ glucose and some magnesium because he had deficiency in his body), it is possible to influence the Na and Cl concentration in the test?

Answer

Hello,
We understand from you that the sweat test was done in a clinical suggestive context, your child having specific symptoms for cystic fibrosis?
First of all, it is important to know, where the sweat test had been done and by which method; only the measurement of the sweat chloride concentration in mmol/l with the “pilocarpin electrophoresis” is a reliable method, sweat conductivity or osmolality not. The test should be performed at an experienced center. So if we assume, that the value you mentioned was 46 mmol/l chloride in the sweat of your 2 year old child, this is not positive nor negative, but in the so-called “intermediate” region (40-59 mmol/l); a clear positive result would be greater than 60 mmol/l. In any case of an intermediate or positive result, the sweat test has to be repeated. Of course, one would assume, that the child shows clinical symptoms suspicious of CF and that this was the reason for doing the sweat test. Typical clinical symptoms and suggestive signs are: steatorrhoeic stools, repeated respiratory infections; poor nutritional status. In case the second sweat test shows again an intermediate result, and the clinical symptoms still point at CF, genetic investigation and other diagnostic tools can be done to clarify the situation. Besides the typical picture of CF and the healthy carrier state there are also atypical forms of the disease when the diagnosis is suspected in certain clinical conditions.
Administration of intravenous solutions mentioned by you does not influence the sweat test, however we do not know, why your child needed an infusion. In case it was very ill or dehydrated or had an infection with strong fever, the sweat test result can be influenced and also be false positive. Therefore, the sweat test should be repeated when your child is healthy at an experienced center with the right method. Together with the clinical picture one would expect to bring light in the situation, as from the data you gave us so far, the diagnose of CF cannot be made nor ruled out. Please return with additional data in order to help you with a complete answer.
Sincerely,
Prof.Dr.Pop L

10.01.2011