Sweat Test

Laboratory Site

WGH

Crewe Road South
Edinburgh
EH4 2XU

Telephone (Biochemistry): 0131 537 1910/1

Special instructions for collection

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Sweat collection

Arrange sweat tests with the Department of Respiratory Medicine. Sweat is collected from a small carefully cleaned area of skin stimulated by pilocarpine, and chloride concentration is measured. Properly performed, this test is valuable in the diagnosis of cystic fibrosis, but reliable results can only be obtained with care, experience and attention to detail. If insufficient sweat is collected, or if abnormal or intermediate results are obtained, a repeat sweat collection may be required.

General additional information

Interpretation

 

All Scottish newborns are screened for cystic fibrosis by immunoreactive trypsin, and a panel of common Scottish cystic fibrosis mutations. Positive results are confirmed by sweat testing. Patients of all ages with symptoms or signs suggestive of cystic fibrosis are also sweat tested, whether or not they have been screened as neonates.

 

Sweat chloride (mmol/L)

0-6months old: <30mmol/L

>6months old: < 40 mmol/L.

 

Children with cystic fibrosis have sweat chloride greater than 60 mmol/L. Normal or intermediate sweat chloride (30/40 – 60mmol/L) may be associated with some mild CFTR mutations. Abnormal results (chloride greater than 60 mmol/L), and intermediate results in the 30/40 - 60 mmol/L range, should always be followed up, by CF mutation analysis and or/ a repeat sweat test.

 

Sweat conductivity is analysed in addition to chloride, however chloride remains the diagnostic parameter. The minimum sweat volume required for reliable interpretation is 1g/m²/min. All collections over 10uL are analysed [Guidelines for the Performance of the Sweat Test for the Investigation of Cystic Fibrosis in the UK. 2^nd edn 2014]