What is the classic test for cystic fibrosis (CF)?

The classic test for cystic fibrosis (CF) is the iontophoresis sweat test. This test measures the concentration of chloride in sweat, which is significantly elevated in individuals with cystic fibrosis. The underlying issue in CF is the mutation of the CFTR gene, leading to defective chloride channels. When sweat is produced, chloride isn't reabsorbed properly in the sweat glands, resulting in higher than normal chloride levels in sweat.

Iontophoresis involves applying a small electric current to stimulate the sweat glands, allowing for the collection of sweat that can then be analyzed for chloride content. This test is a reliable and established method for diagnosing cystic fibrosis in patients, especially in young children.

Other methods, such as CT scans and genetic testing, may provide additional information or support a diagnosis, but they do not serve as the classic or primary diagnostic test for cystic fibrosis. CT scans are more useful for evaluating lung damage in patients already diagnosed with CF, while genetic testing can confirm CF by identifying mutations in the CFTR gene, but does not provide the immediate physiological assessment that the sweat test does. Blood cultures are not specific for diagnosing cystic fibrosis, as they primarily check for infections rather than the underlying defects associated with CF.