What is the best test for detecting cystic fibrosis?

What is the best test for detecting cystic fibrosis?

• A. Sweat chloride
• B. Serum osmolality
• C. Genotype testing
• D. Chest X-ray

Answer: (A)

In diagnosing cystic fibrosis, measuring sweat chloride is the best test because CFTR dysfunction causes markedly elevated chloride in sweat. The process involves stimulating sweat with pilocarpine and collecting sufficient sweat for analysis. In CF, sweat chloride is typically high, often exceeding 60 mmol/L; intermediate or borderline values (around 30–59 mmol/L) may require repeat testing or genetic confirmation, and normal values are usually below 30 mmol/L. This test is the standard confirmatory test in patients with symptoms or after a positive newborn screen. Genetic testing can help in some cases but may miss rare mutations, and imaging like chest X-ray or a non-specific measure like serum osmolality do not diagnose CF.

In diagnosing cystic fibrosis, measuring sweat chloride is the best test because CFTR dysfunction causes markedly elevated chloride in sweat. The process involves stimulating sweat with pilocarpine and collecting sufficient sweat for analysis. In CF, sweat chloride is typically high, often exceeding 60 mmol/L; intermediate or borderline values (around 30–59 mmol/L) may require repeat testing or genetic confirmation, and normal values are usually below 30 mmol/L. This test is the standard confirmatory test in patients with symptoms or after a positive newborn screen. Genetic testing can help in some cases but may miss rare mutations, and imaging like chest X-ray or a non-specific measure like serum osmolality do not diagnose CF.