Sweat chloride in cystic fibrosis
**Core Concept**
Cystic fibrosis is a genetic disorder characterized by the production of thick, sticky mucus due to abnormal **chloride ion transport**. The **cystic fibrosis transmembrane conductance regulator (CFTR)** protein plays a crucial role in regulating chloride ion transport across epithelial membranes.
**Why the Correct Answer is Right**
The correct answer is related to the elevated levels of sweat chloride in cystic fibrosis patients. In normal individuals, the **CFTR** protein helps to reabsorb chloride ions from sweat gland ducts, resulting in low sweat chloride levels. However, in cystic fibrosis patients, the defective **CFTR** protein leads to impaired chloride ion reabsorption, resulting in elevated sweat chloride levels.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately reflect the relationship between cystic fibrosis and sweat chloride levels.
**Option B:** This option is also incorrect as it does not provide a clear understanding of the condition.
**Option C:** This option is incorrect because it is not a characteristic feature of cystic fibrosis.
**Option D:** This option is incorrect as it is not a diagnostic criterion for cystic fibrosis.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that a sweat chloride level above 60 mmol/L is diagnostic of cystic fibrosis.
**Correct Answer:** D. >60 mmol/L