Question

Cystic fibrosis characteristically has the following features EXCEPT

• A. Low levels of sodium and chloride in the sweat
• B. Pancreatic insufficiency
• C. Biliary cirrhosis
• D. Bronchial obstruction

Hint:

Recall which way the sweat electrolytes shift in cystic fibrosis, and why that shift is used as a diagnostic test.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks which of the listed findings is NOT a true feature of cystic fibrosis (CF), an autosomal recessive disorder caused by mutations in the CFTR chloride channel.

Step 2: Key Concept or Approach:
CFTR dysfunction impairs chloride transport across epithelial cells throughout the body. In the sweat glands, this prevents the normal reabsorption of chloride (and secondarily sodium) from sweat as it passes through the duct, so CF patients have abnormally HIGH sweat sodium and chloride, not low - this is the physiological basis of the diagnostic sweat chloride test. Elsewhere in the body, CFTR dysfunction causes abnormally thick, viscous secretions that obstruct the pancreatic ducts, bile ducts, and airways.

Step 3: Working Through the Options:
'Low levels of sodium and chloride in the sweat' is the opposite of the truth - CF sweat is characteristically high in sodium and chloride, which is exactly why the sweat chloride test is diagnostic; this makes it the correct 'except' answer. Pancreatic insufficiency is a genuine, common feature, caused by thick secretions blocking pancreatic ducts and leading to malabsorption. Biliary cirrhosis is a recognised complication from thickened bile obstructing bile ducts over time. Bronchial obstruction from thick, tenacious mucus is the hallmark pulmonary feature of CF, driving recurrent infections and bronchiectasis.

Step 4: Conclusion:
Low sodium and chloride in the sweat is NOT a feature of cystic fibrosis - sweat electrolytes are characteristically elevated.