**Core Concept**
Meconium ileus is a congenital obstruction of the small intestine due to impacted meconium, often associated with cystic fibrosis (CF). CF is a genetic disorder affecting multiple organ systems, including the respiratory, gastrointestinal, and reproductive systems. The underlying defect involves abnormal chloride ion transport across epithelial cells.

**Why the Correct Answer is Right**
The infant's symptoms of persistent steatorrhea (excessive fat in stool) and failure to thrive suggest malabsorption. In CF, the abnormal chloride ion transport leads to thickened secretions in the pancreas, causing pancreatic insufficiency and malabsorption of fats and fat-soluble vitamins. The laboratory test finding most likely related to the infant's underlying disease is a low concentration of pancreatic enzymes, specifically trypsinogen.

**Why Each Wrong Option is Incorrect**
* **Option A:** Elevated sweat chloride levels are a diagnostic marker for cystic fibrosis, but they are not the most likely laboratory test finding related to the infant's malabsorption symptoms.
* **Option B:** Low serum calcium levels can occur in cystic fibrosis due to malabsorption of fat-soluble vitamins, but they are not the most specific finding related to pancreatic insufficiency.
* **Option D:** Elevated liver enzymes can occur in cystic fibrosis due to liver involvement, but they are not the most relevant finding in the context of malabsorption and pancreatic insufficiency.

**Clinical Pearl / High-Yield Fact**
Cystic fibrosis is a multisystem disease that requires a comprehensive approach to diagnosis and management. The presence of meconium ileus in a newborn should prompt further investigation for cystic fibrosis, including sweat chloride testing and genetic analysis.

**Correct Answer:** C. Low trypsinogen levels are indicative of pancreatic insufficiency, which is a key feature of cystic fibrosis.