Cutoff value of sweat chloride values above which 2 consistantly higher reading is diagnostic for Cystic fibrosis is
**Core Concept**
The diagnosis of Cystic Fibrosis (CF) involves measuring sweat chloride levels, which is a key indicator of the disease's presence. The test measures the amount of chloride ions in sweat, and elevated levels are associated with CF.
**Why the Correct Answer is Right**
The World Health Organization (WHO) and the Cystic Fibrosis Foundation recommend that a sweat chloride level of 60 mmol/L or higher is diagnostic for CF. This cutoff value is based on the fact that individuals with CF have a dysfunctional cystic fibrosis transmembrane conductance regulator (CFTR) protein, leading to impaired chloride transport across epithelial cells, including sweat glands. As a result, sweat glands in CF patients produce sweat with higher chloride concentrations.
**Why Each Wrong Option is Incorrect**
* **Option A:** A value of 40 mmol/L is not diagnostic for CF, as it is within the normal range. Sweat chloride levels between 30-59 mmol/L are considered borderline and may require further testing.
* **Option B:** A value of 80 mmol/L is excessively high and is not a diagnostic threshold for CF. It may indicate a false-positive result or an error in the testing procedure.
* **Option C:** A value of 50 mmol/L is not diagnostic for CF, as it is below the recommended cutoff value. However, it may be considered a borderline value and require further evaluation.
**Clinical Pearl / High-Yield Fact**
Remember that a sweat chloride level of 60 mmol/L or higher is diagnostic for Cystic Fibrosis, but a level between 30-59 mmol/L is considered borderline and may require further testing.
**Correct Answer: C. 60 mmol/L or higher**