A nurse is caring for a child who has a suspected diagnosis of cystic fibrosis. Which of the following diagnostic tests will confirm the diagnosis?

A. A stool fat content analysis can indicate malabsorption issues but is not definitive for cystic fibrosis. B. Pulmonary function tests assess lung function but do not confirm cystic fibrosis. C. The sweat chloride test is the primary diagnostic test for cystic fibrosis, as it measures the amount of chloride in sweat, which is elevated in this condition. D. A sputum culture can help identify respiratory infections but does not confirm cystic fibrosis.