In the diagnosis of Cystic Fibrosis, which test is crucial for confirming the condition?

The crucial test for confirming the diagnosis of Cystic Fibrosis is the measurement of sweat chloride levels, particularly when the level is elevated above 60 mmol/L. Cystic Fibrosis is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which affects the function of chloride channels in epithelial cells. In individuals with Cystic Fibrosis, the impaired chloride transport leads to a higher concentration of chloride in sweat. Therefore, when the sweat chloride test indicates a level greater than 60 mmol/L, it is consistent with the diagnosis of Cystic Fibrosis.

While chest imaging can reveal lung abnormalities and genetic testing can confirm the presence of CFTR mutations, these are not diagnostic in themselves. Elevated D-dimer levels are associated with conditions such as thrombosis and are not relevant in the context of Cystic Fibrosis. Similarly, a chest X-ray may show signs of lung disease associated with Cystic Fibrosis, but it cannot confirm the diagnosis of the disorder like the sweat chloride test can. Therefore, high sweat chloride levels are central to diagnosing Cystic Fibrosis, making it a critical diagnostic tool for this condition.