A 2-day-old term neonate has abdominal distension, bilious vomiting, and failure to pass meconium. Contrast enema shows a diffusely small-calibre colon (microcolon) with filling defects in the terminal ileum. Sweat chloride testing in this infant is MOST likely to show which result?

• A Elevated sweat chloride above 60 mmol/L ✓
• B Normal sweat chloride
• C Low sweat chloride below 20 mmol/L
• D Sweat chloride between 30 and 40 mmol/L

Explanation

Microcolon with inspissated meconium pellets in the terminal ileum is meconium ileus, which occurs almost exclusively in cystic fibrosis due to abnormally viscid meconium from defective CFTR chloride transport. The diagnostic sweat test therefore shows elevated sweat chloride above 60 mmol/L. B normal or low value argues against cystic fibrosis. Intermediate values around 30 to 40 mmol/L are borderline and would not fit classic meconium ileus. Hirschsprung disease gives a transition zone rather than microcolon with ileal pellets.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.