Final answer:
Option (c), The most serious systemic complication a nurse should assess for in a patient with regional enteritis is small bowel obstruction, which can lead to life-threatening consequences.
Step-by-step explanation:
A nurse caring for a patient with regional enteritis, also known as Crohn's disease, should be vigilant in assessing for several potential complications. One of the most serious systemic complications that could arise is small bowel obstruction.
This condition can occur due to the inflammation and scarring that are characteristic of Crohn's disease. Other possible complications, though not the most serious systemic ones, include pyelonephritis, megacolon, and nephrolithiasis. Small bowel obstruction is particularly concerning because it can lead to further complications such as sepsis or perforation, which require urgent medical attention.