How does the sweat test help diagnose cystic fibrosis?

The sweat test is not a form of genetic testing; rather, it is a physiological diagnostic tool used to identify cystic fibrosis.

Cystic fibrosis is caused by mutations in the CFTR gene, which impair the function of the CFTR protein responsible for transporting chloride across cell membranes. In individuals with the disorder, this dysfunction affects exocrine glands, including those in the skin. Specifically, it causes the sweat glands to produce perspiration with an abnormally high concentration of sodium chloride (salt).

The sweat test serves as the definitive diagnostic procedure by measuring the salt content in a patient's sweat. While genetic screening can identify carriers or individuals at risk by detecting specific mutations, the sweat test confirms the presence of the disease by measuring this characteristic electrolyte imbalance.1