Sweat Testing

Excerpt

Cystic fibrosis (CF), a rare genetic disorder, characterized by multisystem involvement including progressive, potentially fatal pulmonary disease, has been described as being the most prevalent inherited fatal disorder in the White population of Northern European origin. However, this autosomal recessive disorder also presents in other populations, including African-Americans, Hispanics, and Asians. In patients with CF, Researchers first noted sweat chloride abnormality in CF patients in 1953; this spawned the development of the sweat test in 1959. Since the discovery of the CF gene in 1989, which codes for the protein cystic fibrosis transmembrane regulator (CFTR), there are reports of more than 2000 mutations. The cystic fibrosis transmembrane regulator is at the apical surface of the epithelial cells in the airways, gastrointestinal tract, pancreas, genitourinary system, and the sweat glands in the skin. The defective, deficient or absent CFTR function results in abnormal chloride transport across the chloride channels and abnormal sodium transport along with the secondary effect on water movement across the cell membrane. Decreased chloride secretion along with increased sodium reabsorption (along with water as a secondary effect) across the apical surface of the epithelial cells results in increased viscosity of secretions in the organs involved and in the case of skin, elevated levels of chloride in the sweat. Detection of elevated values of sweat chloride, in a suspected patient, by quantitative pilocarpine iontophoresis test (QPIT) is considered to be the gold standard for the diagnosis of cystic fibrosis.