Following complete ileal partial jejunal resection, the patient is most likely to have?

Correct Answer: B. Vitamin B12 deficiency

Vitamin B12 (cobalamin) is exclusively absorbed in the terminal ileum via intrinsic factor-mediated active transport. Complete ileal resection eliminates this sole site of B12 absorption, making B12 deficiency inevitable regardless of dietary intake or gastric intrinsic factor production. The jejunum, though resected, does not absorb B12—it absorbs iron, calcium, and other nutrients. B12 stores in the liver last 3–5 years, so deficiency manifests insidiously as megaloblastic anemia, peripheral neuropathy (subacute combined degeneration), and glossitis. This is a cardinal consequence of ileal surgery in Indian clinical practice, where post-tuberculosis strictures and Crohn's disease requiring ileal resection are common. Patients require lifelong parenteral B12 supplementation (1000 µg IM monthly or 2000 µg IM every 3 months per Indian guidelines) since oral replacement is futile without the ileal absorptive mechanism.

Why the other options are wrong

A. Gastric ulcer — Gastric ulcer is not a direct consequence of ileal resection. While Zollinger-Ellison syndrome (gastrin-secreting tumour) can cause refractory ulcers, it is unrelated to small bowel resection. The ileum does not regulate gastric acid secretion or mucosal integrity. This is a distractor that confuses post-surgical complications with acid-related pathology. C. Constipation — Ileal resection typically causes diarrhoea, not constipation, due to loss of absorptive surface and increased colonic bile acid load (triggering secretory diarrhoea). Constipation is paradoxically seen after proximal small bowel resection with intact colon. This option reverses the expected pathophysiology and traps students who confuse resection site with bowel motility outcome. D. Folic acid deficiency — Folic acid is absorbed throughout the small intestine, particularly the proximal jejunum. Although jejunal resection occurs here, the ileal resection is complete and the remaining proximal bowel can compensate for folate absorption. B12 has no such redundancy—only the ileum absorbs it. Folate stores last only 3–4 months, but clinical deficiency is less likely than B12 deficiency in this scenario.

High-Yield Facts

Mnemonics

B12 Absorption Site: TERMINAL Terminal ileum is the only site for B12 absorption. Extrinsic factor (B12 in food) + Receptor (intrinsic factor) = Megablast if lost. Intrinsic factor needed. No other site works. Active transport required. Lifelong supplementation needed. Post-Ileal Resection: DIARRHEA (not constipation) Diminished absorption surface. Increased bile acids reach colon. Accelerates transit. Reduces water reabsorption. Resulting secretory diarrhoea. Health consequence: malabsorption. Expect loose stools. Avoid constipation trap.

NBE Trap

NBE pairs ileal resection with "constipation" to trap students who confuse proximal small bowel resection (which can cause constipation due to reduced transit) with ileal resection (which causes diarrhoea). The question also tests whether students know B12 has no redundancy—unlike folate or iron, which are absorbed throughout the small intestine.

Clinical Pearl

In Indian practice, post-tuberculosis ileal strictures requiring resection are common in endemic regions. Patients often present 2–3 years post-surgery with unexplained anaemia and neuropathy—a classic presentation of B12 deficiency that is preventable with early recognition and lifelong IM supplementation. Always counsel patients undergoing elective ileal resection about mandatory B12 monitoring and supplementation.

_Reference: Guyton & Hall Textbook of Medical Physiology (Ch. 65: Secretory and Absorptive Functions); Harrison's Principles of Internal Medicine (Ch. 297: Malabsorption); KD Tripathi Essentials of Medical Pharmacology (B12 metabolism and supplementation)_