Multiple choice

A child presents with history of respitory infections. His sweat chlorides levels are 36 and 41 meq l on two different occasions. Which other test would you do, to exclude the diagnosis of cystic fibrosis?

  1. Repeat sweat chloride measurements

  2. Nasal electrode potential difference

  3. Fat in stool for next 72 hours

  4. DNA analysis for ؤ508 mutation

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Sweat chloride values of 36-41 meq/L are borderline/intermediate (diagnostic is >60, negative <30). Nasal potential difference measurement is the gold-standard confirmatory test when sweat chloride is inconclusive, as it directly assesses CFTR function. DNA analysis has limited utility due to many possible mutations.