Sweat Test (Cystic Fibrosis)

Description: The sweat test is a quantitative measure of chloride in sweat, used in confirming a diagnosis of cystic fibrosis. It may be used in: patients with a phenotype suggestive of cystic fibrosis, patients with a family history of cystic fibrosis, confirmatory testing of a positive newborn screening result, suspicion of an atypical phenotype and monitoring of patients receiving treatment for Cystic Fibrosis.

Clinical details: Cystic fibrosis is the most common lifelong autosomal recessive disease in Northern European populations with an incidence of 1:2500 births. It is less common in the American black population (1:17,000) and rare in Oriental populations (1:90 000). The incidence in the Asian population is less well known, probably around 1:10,000. The typical or classic clinical manifestations of respiratory infection and exocrine pancreatic insufficiency with elevated sweat electrolytes, result from mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene on chromosome 7. Over 1000 mutations at this locus are associated with cystic fibrosis. Clinical features associated with atypical presentation include sino-pulmonary disease, pancreatic sufficiency, idiopathic pancreatitis, isolated male infertility and heat stroke.

Related condition: Cystic Fibrosis

Reference range

Sweat chloride <40 mmol/L - normal, low probability of cystic fibrosis.

Sweat chloride 40-60 mmol/L suggestive, but not diagnostic, of cystic fibrosis.

Sweat chloride >60mmol/L supports a diagnosis of cystic fibrosis.

Reference range for patients under 6 months of age. Normal <30mmol/L. Equivocal 30 mmol/L to 60mmol/L. Positive >60 mmol/L.

Units: mmol/L

Synonyms: Cystic Fibrosis, Sweat Chloride, Chloride, Sweat Test

Testing site: Synnovis : Reference Services : King's College Hospital

Laboratory: Metabolic

Sample type and volume required: Sweat. Volume >20uL. Sweat collection is performed by laboratory staff.

Call in advance: Yes

Special sample instructions: By appointment only - please have patient details ready and call the Metabolic Laboratory on 02032994128 (KCH extension 34128)

Storage and transport: N/A

Turnaround time: 1 day after collection

Patient instructions: N/A

Contacts

Metabolic Laboratory at Blackfriars Hub
Phone: 020 4591 0011
Metabolic Laboratory at Synnovis
Reference Chemistry, Floor One
Friars Bridge Court, 41-43 Blackfriars Road
London, SE1 8NZ

Reference Biochemistry Department at King’s College Hospital
Phone: 020 3299 4107
King’s College Hospital
Denmark Hill
London SE5 9RS

Last updated: 19 June 2026

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