Which test is commonly used to screen for cystic fibrosis by measuring a specific electrolyte in sweat?

Which test is commonly used to screen for cystic fibrosis by measuring a specific electrolyte in sweat?

• A. Sweat chloride test
• B. Blood glucose test
• C. Urine protein test
• D. Serum amylase test

Answer: (A)

Measuring chloride in sweat is used to screen for cystic fibrosis. This works because CFTR gene mutations impair chloride reabsorption in the sweat ducts, so people with cystic fibrosis have higher salt content in sweat. The test collects sweat, often using a small electric current to drive sweat production (pilocarpine iontophoresis) and then measures the chloride concentration. A high sweat chloride level—commonly above about 60 mmol/L—points toward cystic fibrosis and helps confirm the diagnosis, especially after a positive newborn screen or when there’s clinical suspicion. Borderline results may require repeat testing and genetic analysis for certainty. In contrast, the other tests mentioned have different clinical purposes: blood glucose testing screens for diabetes, urine protein testing assesses kidney or urinary tract issues, and serum amylase testing looks for pancreatitis or related conditions.

Measuring chloride in sweat is used to screen for cystic fibrosis. This works because CFTR gene mutations impair chloride reabsorption in the sweat ducts, so people with cystic fibrosis have higher salt content in sweat. The test collects sweat, often using a small electric current to drive sweat production (pilocarpine iontophoresis) and then measures the chloride concentration. A high sweat chloride level—commonly above about 60 mmol/L—points toward cystic fibrosis and helps confirm the diagnosis, especially after a positive newborn screen or when there’s clinical suspicion. Borderline results may require repeat testing and genetic analysis for certainty. In contrast, the other tests mentioned have different clinical purposes: blood glucose testing screens for diabetes, urine protein testing assesses kidney or urinary tract issues, and serum amylase testing looks for pancreatitis or related conditions.