Sweat Testing

Excerpt

Cystic fibrosis is a rare genetic disorder characterized by multisystem involvement, including progressive and potentially fatal pulmonary disease. This condition is considered the most common inherited fatal disorder among individuals of White, Northern European descent. However, cystic fibrosis also occurs in other populations, including African Americans, Hispanics, and Asians. In 1953, researchers first identified abnormalities in sweat chloride levels among patients with cystic fibrosis, which ultimately led to the development of the sweat test in 1959. More than 2,000 mutations have been documented since the 1989 discovery of the cystic fibrosis gene, which codes for the cystic fibrosis transmembrane regulator (CFTR) protein.

The CFTR protein is located on the apical surface of epithelial cells in the airways, gastrointestinal tract, pancreas, genitourinary system, and sweat glands. Defective, deficient, or absent CFTR function disrupts chloride transport across chloride channels, alters sodium transport, and causes secondary effects on water movement across cell membranes. Decreased chloride secretion and increased sodium reabsorption, along with secondary water movement at the apical surface of epithelial cells, lead to increased viscosity of secretions in affected organs. In the skin, these abnormalities result in elevated chloride levels in sweat. The detection of elevated sweat chloride levels using the quantitative pilocarpine iontophoresis test (QPIT) is considered the gold standard for diagnosing cystic fibrosis in suspected cases.