Which sweat test result would not indicate CF?

Which sweat test result would not indicate CF?

• A. 62 mmol/L
• B. 25 mmol/L
• C. 70 mmol/L
• D. 65 mmol/L

Answer: (B)

Sweat chloride testing relies on the fact that CFTR dysfunction in CF reduces the kidney-like reabsorption of chloride in sweat glands, so people with CF typically show a higher-than-normal chloride concentration in their sweat. A result that stays within the normal sweat chloride range does not indicate CF; it sits below the threshold used to diagnose CF. The other values are clearly elevated and would be considered positive for CF in the right clinical context, making them supportive of the diagnosis. In practice, very high results are strongly suggestive of CF, especially when confirmed with repeat testing or supportive genetic testing, while normal results help rule CF out.

Sweat chloride testing relies on the fact that CFTR dysfunction in CF reduces the kidney-like reabsorption of chloride in sweat glands, so people with CF typically show a higher-than-normal chloride concentration in their sweat. A result that stays within the normal sweat chloride range does not indicate CF; it sits below the threshold used to diagnose CF. The other values are clearly elevated and would be considered positive for CF in the right clinical context, making them supportive of the diagnosis. In practice, very high results are strongly suggestive of CF, especially when confirmed with repeat testing or supportive genetic testing, while normal results help rule CF out.