Ambiguous sweat tests

Question

My son (2.5 years old, twin b) due to low weight (he weighs 11.2 kg and is 86.5 cm tall) had 3 sweat tests:
3 October 2011:
1st test: 3/10, result=32
2nd test: 5/10, result=60.

It was recommended to repeat the test another day.
At the new appointment (29-11-2011) the results were: 2/10, result=50.
It was recommended to do a genetic DNA test due to “low perspiration and ambiguous results”.
How much do these values worry you?
I should mention that apart from the “delay in growth” there were no other “suspect” symptoms found in the child.

Answer

Dear friend,
I would like to know if there was another reason for doing the sweat test, apart for the low weight issue. A test of the pancreatic function would suffice. It is impossible to interprete the sweat test results until we do not know which test has been used. Only if the test is performed in an expereinced center and the chloride concentration has been measured by pilocarpine ionotophoresis standardized values exist (over 60mmol/l pathologic, 40-60 mmol/l borderline, under 40 mmmol/l negaitve). Therefore, I would like for you to repeat the sweat test with the method of iontophoresis of pilocarpine. If the values are once more borderline, a genetic analysis or other diagnostic measures are indicated to exclude for sure the diganosis of CF.
Personally I would not worry, because the child does not exhibit more clinical symptoms of CF, but that does not mean that you do not need to examine the issue further.
Yours friendly,
Dr. Stavros Doudounakis

02.07.2012