A 32-year-old woman comes to the clinic due to 6 weeks of bloating and diarrhea. She has multiple watery bowel movements a day without visible blood. The patient underwent Roux-en-Y gastric bypass surgery for morbid obesity 3 years ago and has no other medical conditions. Vital signs are within normal limits. Physical examination is unremarkable. A jejunal aspirate shows a bacterial count of 10⁵/mL, consistent with small intestinal bacterial overgrowth. Which of the following serum levels is most likely to be increased in this patient?

Question

A 32-year-old woman comes to the clinic due to 6 weeks of bloating and diarrhea. She has multiple watery bowel movements a day without visible blood. The patient underwent Roux-en-Y gastric bypass surgery for morbid obesity 3 years ago and has no other medical conditions. Vital signs are within normal limits. Physical examination is unremarkable. A jejunal aspirate shows a bacterial count of >10⁵/mL, consistent with small intestinal bacterial overgrowth. Which of the following serum levels is most likely to be increased in this patient?

Quizplus · Accepted Answer

11ec160b_3ae7_e515_9249_b559f639e314_MD0001_00 Small intestinal bacterial overgrowth (SIBO) is characterized by the proliferation of colonic or oral organisms in the small bowel. It is a common complication of Roux-en-Y gastric bypass surgery; this procedure creates a small gastric pouch, which is removed from the remainder of the stomach and attached to the jejunum via a gastrojejunal anastomosis. The larger bypassed portion of the stomach and duodenum is reattached to the jejunum distally. This results in a closed-ended gastroduodenal limb, in which bacteria can proliferate and ferment any food that may be diverted into this segment. SIBO presents with chronic watery diarrhea due to mucosal inflammation, damage to brush border enzymes, and deconjugation of bile acids (the free bile acids are a direct enterocyte irritant). Bacterial fermentation of unabsorbed carbohydrates produces excessive gas (eg, hydrogen, methane, carbon dioxide) manifesting as bloating and flatulence. In severe cases, fat malabsorption can lead to deficiency of several fat-soluble vitamins (eg, A, D, E) (Choice C). In addition, the enteric bacteria in SIBO produce increased quantities of folate and vitamin K. As a result, serum folate levels may be elevated; vitamin K levels are often normal or only slightly increased because fat malabsorption offsets the increased production. (Choice A) SIBO typically causes cobalamin (vitamin B₁₂) deficiency due to decreased intestinal absorption of both free and intrinsic factor-bound vitamin B₁₂. In addition, the bacteria compete for the uptake and use of vitamin B₁₂. (Choice D) Patients with SIBO often develop zinc deficiency due to malabsorption and nonspecific losses from chronic diarrhea. Educational objective: Small intestinal bacterial overgrowth is a common complication of Roux-en-Y gastric bypass due to excessive bacterial proliferation in the blind-ended gastroduodenal segment. The associated malabsorption can lead to deficiency of many vitamins (eg, A, B₁₂, D, E) but increased production of folate and vitamin K. __________ References: AGA clinical practice update on small intestinal bacterial overgrowth: expert review. (http://www.ncbi.nlm.nih.gov/pubmed/32679220)

A 32-Year-Old Woman Comes to the Clinic Due to 6