What is the primary screening method used to confirm a diagnosis of cystic fibrosis (CF)?

The primary screening method used to confirm a diagnosis of cystic fibrosis (CF) is the sweat test. This test measures the concentration of chloride in sweat. Individuals with cystic fibrosis have defects in the CFTR gene, which affects the transport of chloride and sodium ions across epithelial cell membranes. As a result, people with CF typically have elevated levels of chloride in their sweat.

The sweat test is considered the gold standard for diagnosing cystic fibrosis due to its specificity and reliability. A chloride concentration of greater than 60 millimoles per liter is typically indicative of the disease. This direct method helps clinicians assess the functional impact of CFTR mutations.

In contrast, while genetic testing can identify specific mutations in the CFTR gene, it is usually utilized to confirm a diagnosis rather than serve as the primary screening method. Blood tests may help rule out other conditions but are not specific for cystic fibrosis. Similarly, chest X-rays can indicate lung issues associated with CF, but they do not confirm the presence of the disease. Thus, the sweat test remains the most effective and widely accepted method for diagnosing cystic fibrosis.