Which test is commonly used to diagnose cystic fibrosis?

Which test is commonly used to diagnose cystic fibrosis?

• A. Sweat chloride measurement
• B. Chest X-ray
• C. Serum amylase
• D. Urine protein

Answer: (A)

Measuring chloride in sweat is used to diagnose cystic fibrosis because the defective CFTR protein causes unusually high chloride levels in sweat. The test stimulates sweat production, typically with a small electric current and a topical agent, and then the collected sweat is analyzed for chloride concentration. Clinically, a sweat chloride concentration of 60 mmol/L or higher on two separate occasions confirms CF. Values in the intermediate range (30–59 mmol/L) require additional testing, often including genetic analysis or repeat testing, while a result below 30 mmol/L makes CF unlikely. Other tests listed aren’t diagnostic for CF. Chest X-ray can reveal lung changes that occur with CF but cannot confirm the diagnosis on its own. Serum amylase reflects pancreatic enzyme activity rather than CF status, and urine protein testing isn’t relevant to diagnosing CF.

Measuring chloride in sweat is used to diagnose cystic fibrosis because the defective CFTR protein causes unusually high chloride levels in sweat. The test stimulates sweat production, typically with a small electric current and a topical agent, and then the collected sweat is analyzed for chloride concentration. Clinically, a sweat chloride concentration of 60 mmol/L or higher on two separate occasions confirms CF. Values in the intermediate range (30–59 mmol/L) require additional testing, often including genetic analysis or repeat testing, while a result below 30 mmol/L makes CF unlikely.

Other tests listed aren’t diagnostic for CF. Chest X-ray can reveal lung changes that occur with CF but cannot confirm the diagnosis on its own. Serum amylase reflects pancreatic enzyme activity rather than CF status, and urine protein testing isn’t relevant to diagnosing CF.