A nurse is reinforcing teaching about diagnostic tests with the parents of a child who has suspected cystic fibrosis. Which of the following diagnostic tests should the nurse include as the most definitive when diagnosing cystic fibrosis?

A. The sweat chloride test is considered the most definitive diagnostic test for cystic fibrosis. In this test, sweat is collected from the skin and analyzed for chloride content. Elevated levels of chloride in the sweat are indicative of cystic fibrosis. This test is highly sensitive and specific for diagnosing the condition. B. Stool fat content analysis can help assess pancreatic function and malabsorption, which are common manifestations of cystic fibrosis. However, it is not considered the most definitive test for diagnosing cystic fibrosis. Elevated stool fat content can be suggestive of cystic fibrosis but is not specific to the condition. C. Sputum culture may be performed to identify respiratory pathogens and guide antibiotic therapy in individuals with cystic fibrosis, but it is not the most definitive test for diagnosing the condition. It helps identify infections and monitor lung health but does not confirm the diagnosis of cystic fibrosis. D. Pulmonary function tests are used to assess lung function and airflow, which can be affected in individuals with cystic fibrosis. While these tests provide valuable information about lung health, they are not the most definitive test for diagnosing cystic fibrosis. They are used for monitoring disease progression and response to treatment rather than confirming the diagnosis.