Sweat Test (Cystic Fibrosis)

Overview
Ordering info

Description:

The sweat test, a quantitative measurement of electrolytes in sweat, remains vital in confirming the diagnosis of cystic fibrosis. Indications for sweat testing include:
• Phenotype suggestive of cystic fibrosis
• Family history of cystic fibrosis
• A positive newborn screening test
• Suspicion of an atypical phenotype.

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.

Reference range:

A sweat chloride <40 mmol/L is normal and there is low probability of cystic fibrosis. Chloride 40-60 mmol/L suggestive but not diagnostic of cystic fibrosis. A sweat chloride of >60 mmol/L supports the diagnosis of cystic fibrosis. Suggest repeat sweat test if sweat chloride result >40 mmol/L.

Units:

mmol/L

Department:

Biochemical Sciences Department

Location:

St Thomas' Hospital

Sample type and Volume required:

Sweat collection is performed by laboratory staff.

Turnaround time:

1 day after collection

Special sample instructions:

By appointment only – Please have all clinical information available and contact the laboratory on 020 7188 1264