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sweat test for a baby at the age of 6 months and 20 days

Question
dear Team!

My son (6 months old) will have in 2 weeks a sweat test because he suffers from bronchitis very oft (5 times during 2 last months) and a very salty forehead. On the day of testing he will be 6 months and 20 days old? what are the normal results for thi age? 39 or 29???
thank you veru much in advance!!!!!
Answer
Dear Questioner
Many thanks for your question. You say your son will undergo the sweat test soon. This is one of a range of tests that can be done to confirm or rule out a diagnosis of CF. Others include genetic tests for CF causing mutations (used routinely), nasal potential difference (used less often) and intestinal current measurement (used less often again).

A sweat chloride of 60 mmol/L indicates a positive result and between 30 and 60 mml/L indicates an equivocal result. However it should be stated that the diagnosis of cystic fibrosis is based not only on the result of the sweat test but also takes into consideration the clinical presentation and other tests performed (i.e. genetic tests). (De Boeck et al 2006)

There is another guidelines about the sweat test, that can be cited as follows (Farrell et al. in the Journal of Pediatrics 2008; 153:S4-S14 “Guidelines for Diagnosis of Cystic Fibrosis in Newborns through Older adults: Cystic Fibrosis Foundation Consensus Report”):
"Based on the available data on sweat chloride test results in healthy and CF-affected infants the consensus committee recommends the following sweat chloride reference rages for infatns up to age 6 months: below or equal 29 mmol/l, CF unlikely; 30 to 59 mmol/l, intermediate; over or equal 60 mmol/l, indicative of CF.
Based on the available data on sweat chloride test results beyond infancy, the consensus committee recommends the following sweat chloride reference rages for individuals over age 6 months: below or equal 39 mmol/l, CF unlikely; 40 to 59 mmol/l , intermediate; over or equal 60 mmol/l, indicative of CF. "

That means, if you child is 6 months and 20 days at the age of testing, the value, that is considered still to be normal, rises from 29 to 39 mmol/l. Another important point is that the test is carried out at an experienced center using the so-called "pilocarpine ionotophoresis" to measure the chloride concentration in the sweat in order to get reliable results.

We would recommend that you share your concerns with the team who are performing the sweat test for your son.

Best wishes,
Lisa Kent and Laura Jenkins
(Belfast)


References:
De Boeck et al. Cystic Fibrosis: Terminology and Diagnostic Algorithms. Thorax 2006;61:627-635
www.ncbi.nlm.nih.gov/pmc/articles/PMC2104676/pdf/627.pdf

15.10.2013
The answer is edited by: PhD Lisa Kent