Sweat test

Chemical Pathology

Notes

Cystic Fibrosis affects 1 in 2500 infants born in the UK. Early identification and treatment is useful for optimal treatment of symptoms.
Cystic fibrosis is one of the conditions tested for in new born infants as part of the UK New-born Screening Program.
Sweat tests are used along with genetic testing in the follow up investigation of infants with an abnormal newborn screening test for cystic fibrosis and are designed to detect the elevated levels of electrolytes in the sweat of children with this condition.
Testing is performed by qualified Healthcare Scientists trained in this procedure in the Paediatric Outpatients Department.
Requests should be from a paediatric consultant with testing available by prior appointment only.
Requests forms for this investigation should be sent to the “Department of Chemical Pathology at Gloucestershire Royal Hospital” and an appointment will then be made.
Rarely this test may be performed in an adult patient. Please contact the duty biochemist to arrange an appointment if this is required.

Turnaround times

Once the test has been performed, the samples are assayed locally in the Department of Chemical Pathology, with results normally made available within 3 working days.

Reference ranges and result Interpretation

Interpretation of sweat chloride (based on National Guidelines published March 2014)

Children less than 6 months of age:

• A sweat chloride of <30 mmol/L in patients <6 months of age makes CF unlikely but requires genetic and clinical correlation.

• A chloride concentration of 30-60 mmol/L if less than 6 months of age is an intermediate result which requires further cystic fibrosis assessment such as a repeat test and or further investigations.

• A sweat chloride concentration of > 60 mmol/L supports the diagnosis of CF.

Children greater than 6 months of age:

• A sweat chloride of <40 mmol/L makes cystic fibrosis unlikely but requires genetic and clinical correlation.

• A sweat chloride concentration of 40 - 60 mmol/L is an intermediate result which requires further cystic fibrosis assessment such as a repeat test and /or further investigations.

• A sweat chloride concentration of >60 mmol/L supports the diagnosis of cystic fibrosis.