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ABIM GI Practice Questions (2026) — Free Sample Questions with Answers

15 free ABIM GI questions from our 150-question bank, grouped by content domain. Each answer explains why the right option is right — and why every wrong option is wrong.

Procedures and Periprocedural Issues (2)Esophageal Disorders (1)Inflammatory Bowel Disease and Other Immune-Related Disorders (1)Motility Disorders (1)Neoplastic Disorders (2)Liver Disorders (3)Pancreas and Biliary Tract Disorders (1)Disorders of Gut–Brain Interaction (2)Other Disorders (2)
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Procedures and Periprocedural Issues

Question 1

A 74-year-old man with nonvalvular atrial fibrillation (CHA2DS2-VASc score 3) is scheduled for endoscopic mucosal resection of a 30-mm cecal adenoma. He takes apixaban 5 mg twice daily. He has no history of stroke, transient ischemic attack or venous thromboembolism. Weight is 78 kg. He takes no antiplatelet drugs, and his last colonoscopy was 6 years ago. His estimated creatinine clearance is 48 mL/min. The procedure is planned for a Monday morning. Laboratory studies are shown. Which of the following is the most appropriate periprocedural plan for apixaban?

Laboratory studies
TestResultReference range
Creatinine1.6 mg/dL0.70–1.30 mg/dL
Hemoglobin13.9 g/dL14–18 g/dL
Platelet count210,000/μL150,000–450,000/μL
Show answer & explanation

Answer: B

Continue apixaban without interruption: Continuation suits warfarin in many settings, but ACG–CAG 2022 suggests interrupting DOACs before elective procedures, and this resection carries high bleeding risk.

Omit for 2 days before; no bridging: Correct. ACG–CAG 2022 suggests temporary interruption of DOACs without bridging. Using the PAUSE protocol, apixaban is omitted for 2 days before a high-bleeding-risk procedure, and this applies at a creatinine clearance of 48 mL/min.

Omit for 3 days before; no bridging: A longer hold adds stroke risk without reducing bleeding; apixaban clearance depends little on the kidney.

Omit for 4 days before; no bridging: Four days is the hold for dabigatran with creatinine clearance 30–49 mL/min before high-risk procedures, not apixaban.

Omit for 5 days with enoxaparin bridging: Bridging is not recommended; it raises bleeding without preventing thromboembolism, and DOACs wear off quickly.

Hold DOACs (do not bridge) before elective high-risk endoscopy: apixaban, rivaroxaban or edoxaban for 2 days; dabigatran longer when creatinine clearance is under 50 mL/min.

Question 2

A 69-year-old man undergoes screening colonoscopy. In the sigmoid colon there is an 18-mm slightly elevated lesion with a central depressed area (Paris 0-IIa+IIc). The depressed area is reddish and firm, and its surface pattern is lost. Narrow-band imaging of the depression shows amorphous areas with thick, interrupted vessels (JNET type 3). The lesion has never been biopsied or manipulated, but after submucosal injection the central area does not lift. The rest of the colon is normal. Which of the following is the most likely histologic finding?

Show answer & explanation

Answer: D

Adenoma with low-grade dysplasia: Low-grade adenomas show regular pit and vessel patterns (JNET 2A) and lift with injection.

Adenoma with high-grade dysplasia: High-grade dysplasia or superficial invasion maps to JNET 2B; it does not produce amorphous areas and a nonlifting depression.

Intramucosal adenocarcinoma: Intramucosal cancer can be removed endoscopically and usually lifts well; it lacks JNET 3 features.

Deep submucosal invasive adenocarcinoma: Correct. A depressed (0-IIc) component, loss of surface pattern, JNET type 3 vessels and a nonlifting sign without prior manipulation predict deep submucosal invasion (≥1000 μm). The lesion should be biopsied and tattooed and the patient referred for surgery rather than resected endoscopically.

Sessile serrated lesion with dysplasia: Serrated lesions are pale, mucus-capped and usually proximal; they do not show this depressed, nonlifting morphology.

Depression, lost surface pattern, JNET 3 and a nonlifting sign in an untouched lesion predict deep submucosal invasion: biopsy, tattoo and refer for surgery.

Esophageal Disorders

Question 3

A 46-year-old woman is evaluated for 8 months of heartburn and regurgitation that persist despite 8 weeks of omeprazole 40 mg twice daily taken 30 minutes before breakfast and dinner. She has no dysphagia, weight loss, anemia or vomiting. She has never had reflux testing. Upper endoscopy while on omeprazole shows a normal esophagus without erosive esophagitis, Barrett esophagus or hiatal hernia, and esophageal biopsy specimens are normal. Which of the following is the most appropriate next diagnostic test?

Show answer & explanation

Answer: C

pH-impedance monitoring on twice-daily PPI: Monitoring on PPI is for patients with already proven GERD (prior LA grade C/D esophagitis, long-segment Barrett or abnormal pH study) who remain symptomatic.

High-resolution esophageal manometry: Manometry is not a reflux test; it is used to place pH catheters and before antireflux surgery.

Wireless pH monitoring off PPI for 96 hours: Correct. GERD has never been proven, and a normal endoscopy on PPI does not exclude it. ACG 2022 and Lyon Consensus 2.0 advise prolonged wireless pH monitoring after stopping PPI for 7 days; acid exposure time >6% confirms GERD and <4% excludes it.

Barium esophagram: Barium reflux is neither sensitive nor specific for GERD.

Gastric emptying scintigraphy: Gastric emptying testing is for suspected gastroparesis, which is not the leading concern here.

PPI-refractory symptoms without proven GERD: test off PPI (prolonged wireless pH monitoring); test on PPI only when GERD has already been proven.

Inflammatory Bowel Disease and Other Immune-Related Disorders

Question 4

A 29-year-old woman with ulcerative colitis is in hospital on day 3 of intravenous methylprednisolone 60 mg daily for acute severe colitis. She still has eight bloody stools daily. Temperature is 37.8 °C (100.0 °F) and pulse rate is 102/min. The abdomen is mildly tender without distention; abdominal radiograph shows a transverse colon diameter of 4.5 cm. Stool testing for Clostridioides difficile is negative, and sigmoidoscopy biopsies show no cytomegalovirus. She receives enoxaparin prophylaxis. Tuberculosis and hepatitis B screening are negative. Laboratory studies are shown. Which of the following is the most appropriate next step?

Laboratory studies, hospital day 3
TestResultReference range
Hemoglobin9.8 g/dL12–16 g/dL
C-reactive protein9.6 mg/dL≤0.8 mg/dL
Albumin2.7 g/dL3.5–5.5 g/dL
Potassium3.6 mEq/L3.5–5.0 mEq/L
Show answer & explanation

Answer: C

Continue methylprednisolone for 4 more days: Prolonging steroids beyond day 3 without response delays rescue therapy and raises the risk of emergency colectomy.

Vedolizumab induction: Vedolizumab acts too slowly for steroid-refractory acute severe colitis.

Infliximab 5 mg/kg intravenously: Correct. Persistent frequent bloody stools and a CRP above 4.5 mg/dL on day 3 of intravenous steroids predict steroid failure (Oxford criteria). ACG recommends medical rescue with infliximab (or cyclosporine), with surgical consultation; infection has been excluded.

Total colectomy now: Urgent colectomy is for toxic megacolon, perforation, massive bleeding or failed rescue therapy; she has none of these yet.

Add oral mesalamine 4.8 g daily: Mesalamine has no role in rescuing acute severe colitis.

Acute severe UC not responding by day 3 of intravenous steroids: rescue with infliximab or cyclosporine, with early surgical consultation.

Motility Disorders

Question 5

A 59-year-old woman is evaluated for 18 months of dysphagia to solids and liquids and episodes of severe chest pain while eating. Cardiac evaluation is normal. Upper endoscopy shows no mass or stricture, and CT of the chest shows no extrinsic compression. A timed barium esophagram shows a corkscrew esophagus with a 4-cm barium column at 5 minutes. High-resolution manometry findings are shown. She is otherwise healthy and wants definitive treatment. Which of the following is the most appropriate treatment?

High-resolution manometry (10 supine wet swallows)
MetricResultNormal (typical values)
Median integrated relaxation pressure (supine)24 mm Hg≤15 mm Hg
Normal peristalsis0 of 10 swallows—
Premature contractions (distal latency <4.5 s)7 of 10 swallowsNone
Distal contractile integral of premature swallows3200–6800 mm Hg·s·cm450–8000 mm Hg·s·cm
Show answer & explanation

Answer: E

Botulinum toxin injection: Botulinum toxin gives temporary relief and is reserved for patients who are poor candidates for definitive therapy.

Nifedipine before meals: Calcium channel blockers are least effective and cause adverse effects; they are not definitive therapy.

Pneumatic dilation to 30 mm: Pneumatic dilation treats only the sphincter and works poorly for the spastic body of type III achalasia.

Laparoscopic Heller myotomy with Dor fundoplication: Heller myotomy works well for types I and II, but its limited proximal extent often fails to cover the spastic segment in type III.

Peroral endoscopic myotomy: Correct. Elevated IRP, no normal peristalsis and premature contractions in ≥20% of swallows define type III achalasia. ACG 2020 suggests POEM because a myotomy tailored to the length of the spastic segment gives the best results.

Type III (spastic) achalasia responds best to POEM with a myotomy covering the spastic segment; types I and II respond to POEM, Heller myotomy or pneumatic dilation.

Neoplastic Disorders

Question 6

A 51-year-old man (III-1) is seen after cascade testing showed that he carries the pathogenic BRCA2 variant first found in his paternal aunt (see pedigree). His father died of pancreatic adenocarcinoma diagnosed at 66. No other relative has had pancreatic cancer. He has no abdominal symptoms, does not smoke, drinks rarely, and has no diabetes. Examination and liver chemistry tests are normal. His primary care physician told him that pancreatic screening is "only for families with two pancreatic cancers."

Which of the following is the most appropriate recommendation regarding pancreatic cancer surveillance?

Family pedigree
IIIIIII-1: Prostate ca 70, d. 74I-2: d. 88II-1: 75 yII-2: Pancreatic ca 66, d. 67II-3: Breast ca 45, 70 yIII-1: 51 y, BRCA2+III-2: 48 y, untested
Shaded symbols = cancer; slash = deceased; arrow = the patient; BRCA2+ = known pathogenic BRCA2 variant.
Show answer & explanation

Answer: C

No surveillance unless a second relative is affected: Applies the familial pancreatic cancer rule for people without a variant; a BRCA2 carrier needs only one affected first-degree relative.

Annual EUS or MRI/MRCP starting at age 56: Wrong threshold: 10 years before the father's diagnosis (56) is later than age 50, so the earlier age applies.

Annual EUS or MRI/MRCP starting now: Correct. BRCA2 carriers with at least one first-degree relative with pancreatic cancer qualify for surveillance. It starts at age 50, or 10 years before the youngest affected relative was diagnosed, whichever is earlier. At 51 he should start now, with EUS and/or MRI/MRCP.

Annual serum CA 19-9 measurement alone: CA 19-9 lacks the sensitivity for early lesions and is not a stand-alone screening test.

Annual contrast-enhanced CT of the abdomen: CT is less sensitive for small cysts and early lesions than EUS or MRI and adds yearly radiation.

Carriers of BRCA1/2, PALB2, ATM or Lynch genes with a first-degree relative with pancreatic cancer get EUS and/or MRI surveillance from age 50, or 10 years before the earliest family diagnosis if that is sooner.

Question 7

A 58-year-old woman undergoes right hemicolectomy for a stage II adenocarcinoma of the ascending colon. Her family history is limited: her mother died at 70 of a stroke, and she has one healthy brother aged 55. She has no personal history of other cancers. As part of universal tumor screening, the pathologist performs mismatch repair immunohistochemistry and microsatellite testing on the resected tumor (see table). She asks whether her children need to be tested.

Which of the following is the most appropriate next step?

Tumor mismatch repair testing
MarkerResult
MLH1Loss of nuclear staining
PMS2Loss of nuclear staining
MSH2Retained
MSH6Retained
Microsatellite statusMSI-high
Show answer & explanation

Answer: B

  1. MLH1 and PMS2 are lost together because PMS2 is unstable without MLH1, so the defect is at MLH1.
  2. MLH1 loss in an older patient is usually somatic promoter hypermethylation (BRAF V600E often present).
  3. Test the tumor for BRAF V600E or MLH1 methylation: if present, sporadic; if absent, refer for germline testing.

Germline MLH1 sequencing: Right test, wrong order: in a 58-year-old with this pattern, sporadic methylation is the likeliest cause and should be excluded first.

Tumor BRAF V600E or MLH1 methylation test: Correct. Combined MLH1/PMS2 loss is most often sporadic, caused by somatic MLH1 promoter hypermethylation (usually with BRAF V600E). Testing the tumor for BRAF V600E or MLH1 promoter methylation comes first; only if neither is present is germline testing indicated.

Germline PMS2 sequencing: PMS2 loss here is secondary to loss of its MLH1 partner; isolated PMS2 loss would point to PMS2.

Germline MSH2 and EPCAM testing: That is the work-up for MSH2/MSH6 loss, the sibling pattern; MSH2 is retained here.

Classify as sporadic with no further testing: Premature: a minority of MLH1/PMS2-deficient tumors are Lynch syndrome, so methylation/BRAF status must be checked before calling it sporadic.

Tumor MLH1/PMS2 loss calls for BRAF V600E or MLH1 promoter methylation testing before germline testing; MSH2/MSH6 or isolated MSH6/PMS2 loss goes straight to germline testing.

Liver Disorders

Question 8

A 49-year-old man with chronic hepatitis B, taking tenofovir alafenamide for 4 years with undetectable HBV DNA, returns for annual review. He has never had decompensation. Ultrasonography shows a mildly coarse liver without nodularity or splenomegaly and no focal lesion. Vibration-controlled transient elastography shows a liver stiffness of 12.4 kPa with a valid IQR. Laboratory results are shown. He asks whether he needs an upper endoscopy to look for varices.

Which of the following is the most appropriate recommendation?

Laboratory results
TestResultReference range
Platelet count212,000/μL150,000–450,000/μL
Albumin4.2 g/dL3.5–5.5 g/dL
Total bilirubin0.7 mg/dL0.3–1.0 mg/dL
ALT28 U/L10–40 U/L
Show answer & explanation

Answer: D

Upper endoscopy now: Not needed: the Baveno VII criteria (LSM <20 kPa, platelets >150,000/μL) safely spare endoscopy.

Start carvedilol: Carvedilol is for CSPH (LSM ≥25 kPa); CSPH is unlikely at 12.4 kPa with normal platelets.

Hepatic venous pressure gradient measurement: Invasive and not needed when noninvasive tests are reassuring.

Repeat elastography and platelets in 12 months: Correct. Under Baveno VII, compensated advanced chronic liver disease with LSM <20 kPa and platelets >150,000/μL has a very low probability of varices needing treatment, so screening endoscopy can be avoided. Annual repeat elastography and platelet count track progression, alongside HCC surveillance for HBV.

Discharge from liver follow-up: LSM >10 kPa suggests compensated advanced chronic liver disease, and HBV needs ongoing HCC surveillance.

Baveno VII: LSM <20 kPa and platelets >150,000/μL → no screening endoscopy; repeat elastography and platelets yearly.

Question 9

A 58-year-old man with alcohol-associated cirrhosis and refractory ascites is in the ICU with acute kidney injury. Creatinine rose from 1.1 to 2.9 mg/dL over 5 days and did not improve after stopping diuretics and giving IV albumin 1 g/kg daily for 2 days. Urine sodium is 8 mEq/L, urinalysis is bland, and renal ultrasonography is normal. He received no nephrotoxins or contrast, and infection workup is negative. Blood pressure is 96/58 mm Hg. Oxygen saturation is 88% on room air, with bibasilar crackles; chest radiograph shows mild interstitial edema. A central venous catheter is in place.

Which of the following is the most appropriate treatment?

Show answer & explanation

Answer: D

Terlipressin plus albumin: First-line for HRS-AKI, but contraindicated by his hypoxemia and pulmonary edema.

Midodrine, octreotide and albumin: Less effective; used only when neither terlipressin nor norepinephrine is feasible.

Transjugular intrahepatic portosystemic shunt: Not first-line for HRS-AKI, and risky with this degree of liver and renal dysfunction.

Norepinephrine infusion plus albumin: Correct. This is HRS-AKI. Terlipressin plus albumin is usually first-line, but terlipressin can cause fatal respiratory failure and should not be given with SpO2 <90% or volume overload. In the ICU with central access, norepinephrine plus albumin is the effective alternative.

Continue albumin alone for 48 more hours: Two days of volume expansion without response already meets HRS-AKI criteria; more delay lowers the response rate.

HRS-AKI: vasoconstrictor plus albumin; terlipressin is first-line except with hypoxemia (SpO2 <90%) or volume overload, when norepinephrine in the ICU is used.

Question 10

A 19-year-old woman is admitted with 10 days of jaundice, fatigue and new confusion. She takes no medications or supplements and denies acetaminophen use. She is drowsy but arousable, with asterixis and scleral icterus. Ultrasonography shows a small nodular liver with patent vessels. The direct antiglobulin test is negative, and the peripheral smear shows spherocytes. Viral hepatitis serologies are negative. Laboratory results are shown.

Which of the following is the most likely diagnosis?

Laboratory results
TestResultReference range
Hemoglobin8.6 g/dLF 12–16 g/dL
AST214 U/L10–40 U/L
ALT78 U/L10–40 U/L
Alkaline phosphatase24 U/L30–120 U/L
Total bilirubin22.4 mg/dL0.3–1.0 mg/dL
INR2.9(normal 0.8–1.1)
Ceruloplasmin17 mg/dL25–43 mg/dL
Show answer & explanation

Answer: C

  1. ALP:total bilirubin = 24/22.4 ≈ 1.1, i.e., <4.
  2. AST:ALT = 214/78 ≈ 2.7, i.e., >2.2.
  3. Both ratios plus Coombs-negative hemolysis → fulminant Wilson disease.

Autoimmune hepatitis: Can cause ALF in young women, but does not explain Coombs-negative hemolysis or the very low ALP.

Herpes simplex hepatitis: Usually anicteric with aminotransferases in the thousands, the opposite of this pattern.

Wilson disease: Correct. Coombs-negative hemolysis, only modestly raised aminotransferases, an AST:ALT ratio >2.2 and an ALP:bilirubin ratio <4 (here about 1) identify fulminant Wilson disease. Ceruloplasmin is unreliable in acute liver failure. This presentation is fatal without urgent liver transplantation.

Acetaminophen hepatotoxicity: Causes aminotransferases in the thousands with relatively low bilirubin early on.

Acute Budd–Chiari syndrome: Patent hepatic veins on ultrasonography, and no hemolysis or ALP pattern to support it.

Acute liver failure with Coombs-negative hemolysis, ALP:bilirubin <4 and AST:ALT >2.2 indicates Wilson disease; list the patient urgently for transplant.

Pancreas and Biliary Tract Disorders

Question 11

A 62-year-old woman has had 2 days of postprandial right upper quadrant pain that is now improving. She is afebrile, blood pressure is 132/80 mm Hg, and pulse is 84/min. She has mild right upper quadrant tenderness without jaundice. Ultrasonography shows multiple gallbladder stones without wall thickening and a 7-mm common bile duct; no duct stone is seen. Lipase is normal. Laboratory results are shown. Surgery plans laparoscopic cholecystectomy this admission, and the hospital does not perform intraoperative cholangiography routinely.

Which of the following is the most appropriate next step?

Laboratory results
TestResultReference range
Total bilirubin2.6 mg/dL0.3–1.0 mg/dL
Alkaline phosphatase214 U/L30–120 U/L
ALT186 U/L10–40 U/L
AST148 U/L10–40 U/L
Leukocyte count8,200/μL4,000–11,000/μL
Show answer & explanation

Answer: C

ERCP with sphincterotomy: High-risk criteria are not met (duct stone on imaging, cholangitis, or bilirubin >4 mg/dL with a dilated duct); ERCP first exposes her to avoidable pancreatitis risk.

Laparoscopic cholecystectomy without duct evaluation: Ignores an intermediate probability of a duct stone when no intraoperative cholangiography is planned.

Endoscopic ultrasonography: Correct. Under ASGE 2019 criteria, abnormal liver tests, age >55 and a dilated duct are intermediate risk: bilirubin is ≤4 mg/dL, no stone is seen and there is no cholangitis. Intermediate risk calls for EUS (or MRCP) before cholecystectomy, saving ERCP for confirmed stones.

Hepatobiliary iminodiacetic acid scan: Assesses cystic duct patency (acute cholecystitis), not duct stones.

Contrast-enhanced CT of the abdomen: Misses many radiolucent duct stones; it is not the preferred test here.

ASGE 2019: high risk (duct stone on imaging, cholangitis, or bilirubin >4 mg/dL with a dilated duct) → ERCP; intermediate risk (abnormal liver tests, age >55, dilated duct) → EUS, MRCP or intraoperative cholangiography.

Disorders of Gut–Brain Interaction

Question 12

A 37-year-old woman is evaluated for daily retrosternal burning for 2 years that has not improved with 12 weeks of omeprazole 40 mg twice daily. Upper endoscopy with biopsies is normal, and high-resolution manometry is normal. She has no dysphagia, regurgitation, cough or weight loss, and she is anxious about the possibility of cancer. She stopped omeprazole 7 days before 24-hour pH-impedance monitoring, during which she recorded 12 heartburn episodes. Results are shown. Which of the following is the most likely diagnosis?

24-hour pH-impedance monitoring off PPI
MeasureResultNormal or threshold
Acid exposure time1.8%<4% normal; >6% abnormal
Total reflux episodes31<40
Symptom index17%Positive ≥50%
Symptom association probability42%Positive ≥95%
Show answer & explanation

Answer: E

Nonerosive reflux disease: Nonerosive reflux disease requires abnormal acid exposure (>6%); hers is normal.

Reflux hypersensitivity: Reflux hypersensitivity has normal acid exposure but a positive symptom index or symptom association probability; both are negative.

Eosinophilic esophagitis: EoE is excluded by normal esophageal biopsies.

Ineffective esophageal motility: Manometry is normal, and weak motility would not explain burning without reflux.

Functional heartburn: Correct. Rome IV functional heartburn: retrosternal burning despite PPI, with normal endoscopy and biopsies, no major motor disorder, normal acid exposure and no association between symptoms and reflux events. Treatment is a neuromodulator or behavioral therapy, not escalating acid suppression or surgery.

Normal acid exposure: positive symptom association means reflux hypersensitivity, negative means functional heartburn.

Question 13

A 33-year-old woman with IBS with constipation by Rome IV criteria is evaluated for continued abdominal pain and bloating with hard stools three times weekly. Over the past 6 months she tried soluble fiber and then polyethylene glycol 17 g daily; stool frequency improved slightly, but pain and bloating did not. Celiac serology and a complete blood count are normal. She has no alarm features, is not pregnant, and has no history of bowel obstruction. Which of the following is the most appropriate next treatment?

Show answer & explanation

Answer: C

Higher-dose polyethylene glycol: Polyethylene glycol improves stool frequency, but ACG 2021 suggests against it for global IBS-C symptoms because it does not relieve pain.

Alosetron: Alosetron is a 5-HT3 antagonist for women with severe IBS with diarrhea; it would worsen constipation.

Linaclotide: Correct. ACG 2021 recommends guanylate cyclase-C agonists (linaclotide, plecanatide) for global IBS-C symptoms; they improve both stool frequency and abdominal pain.

Rifaximin for 14 days: Rifaximin is recommended for IBS with diarrhea, not constipation.

Loperamide as needed: Loperamide slows transit and would worsen constipation.

For IBS-C not controlled by fiber, use a guanylate cyclase-C agonist; rifaximin, alosetron and loperamide are IBS-D treatments.

Other Disorders

Question 14

A 73-year-old woman with atrial fibrillation is evaluated for 8 hours of right lower quadrant pain followed by a small amount of maroon stool. She stopped warfarin 2 weeks ago before a dental procedure and has not restarted it. Pulse rate is 104/min (irregular) and blood pressure is 132/78 mm Hg. There is moderate right-sided abdominal tenderness without peritoneal signs. CT of the abdomen with oral and intravenous contrast (portal venous phase) shows segmental wall thickening of the ascending colon and cecum with pericolic stranding; the transverse and left colon are normal. Laboratory studies are shown. Which of the following is the most appropriate next diagnostic step?

Laboratory studies
TestResultReference range
Leukocyte count14,200/μL4000–11,000/μL
Hemoglobin12.8 g/dL12–16 g/dL
Lactate, serum2.6 mmol/L0.7–2.1 mmol/L
Creatinine0.9 mg/dL0.50–1.10 mg/dL
Show answer & explanation

Answer: C

Colonoscopy within 48 hours: Colonoscopy confirms colon ischemia, but in isolated right colon ischemia the priority is to exclude a threatening SMA occlusion.

Repeat CT in 48 hours: Waiting misses the window to treat acute mesenteric ischemia.

CT angiography of the mesenteric vessels: Correct. Isolated right colon ischemia often reflects superior mesenteric artery occlusion and carries higher mortality. ACG 2015 recommends noninvasive vascular imaging (CT angiography) to exclude acute mesenteric ischemia; her atrial fibrillation off anticoagulation and raised lactate add to the concern.

Stool testing for Clostridioides difficile: Infection is in the differential, but the vascular cause must be excluded first.

Echocardiography for a cardiac thrombus: Echocardiography may follow, but it does not assess the mesenteric circulation.

Isolated right colon ischemia warrants CT angiography to exclude superior mesenteric artery occlusion (acute mesenteric ischemia).

Question 15

A 52-year-old woman is evaluated for 4 months of watery diarrhea, five or six stools daily, that stops when she fasts for 48 hours. She takes an over-the-counter "digestive health" supplement, a calcium–magnesium product and a multivitamin. She has no weight loss or nocturnal stools. Colonoscopy with random biopsies, celiac serology and stool pathogen tests are normal. A 48-hour stool collection shows a daily volume of 650 g. Stool results are shown. Which of the following is the most likely cause of her diarrhea?

Stool water studies
TestResult
Sodium30 mEq/L
Potassium25 mEq/L
Measured osmolality296 mOsm/kg
pH7.1
Calculate the osmotic gap using an assumed stool osmolality of 290 mOsm/kg.
Show answer & explanation

Answer: D

  1. Osmotic gap = 290 − 2 × (stool Na + stool K).
  2. 2 × (30 + 25) = 110 mOsm/kg.
  3. Gap = 290 − 110 = 180 mOsm/kg, well above 125, so the diarrhea is osmotic.
  4. A pH above 6 argues against carbohydrate malabsorption; with resolution on fasting and a magnesium supplement, unabsorbed magnesium is the likely solute.

Microscopic colitis: Microscopic colitis is a secretory diarrhea with a low osmotic gap, and her random biopsies were normal.

Bile acid diarrhea: Bile acid diarrhea is secretory, with a gap under 50 mOsm/kg, and usually persists during a fast.

Surreptitious stimulant laxative use: Stimulant laxatives such as senna or bisacodyl cause secretory diarrhea with a low osmotic gap.

Magnesium-induced osmotic diarrhea: Correct. The osmotic gap is 290 − 2(30 + 25) = 180 mOsm/kg (>125, osmotic). Diarrhea that stops with fasting, a stool pH above 6 (against carbohydrate malabsorption) and a magnesium-containing supplement point to magnesium as the unabsorbed solute.

Lactose malabsorption: Carbohydrate malabsorption is osmotic, but colonic fermentation would lower stool pH below 6.

Stool osmotic gap = 290 − 2(Na + K): >125 osmotic (magnesium, carbohydrates), <50 secretory; low stool pH points to carbohydrate malabsorption.

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