Undifferentiated abdominal pain accounts for 5–10% of all emergency department visits, with over 150 possible etiologies. The most common diagnoses are gastroenteritis (10.8%) and nonspecific abdominal pain (10.4%), followed by cholelithiasis, urolithiasis, diverticulitis, and appendicitis. [1] Approximately 15–20% of ED patients with acute abdominal pain require interventional or surgical treatment, and mortality ranges from 2–12%, rising with each hour of delay to definitive treatment. [2]
The following AAFP diagnostic algorithm provides a structured approach to evaluation:
1. History
- Onset and character: Sudden/maximal onset → consider perforation, ruptured AAA, volvulus, ischemia. Gradual → appendicitis, cholecystitis, diverticulitis [1][3]
- Location: Pain location is the single most useful starting point for narrowing the differential [4]
- RUQ: biliary disease, hepatitis, pneumonia
- LLQ: diverticulitis, ovarian pathology
- RLQ: appendicitis, Meckel's, ovarian torsion
- Epigastric: PUD, pancreatitis, GERD, MI
- Periumbilical → RLQ migration: classic appendicitis (50–60% of cases) [5]
- Timing: Postprandial → biliary colic, mesenteric ischemia. Nocturnal → duodenal ulcer [6]
- Associated symptoms: Nausea/vomiting (SBO, gastroenteritis, appendicitis), fever (cholecystitis, appendicitis, diverticulitis), diarrhea (gastroenteritis, IBD, ischemic colitis), obstipation (SBO), hematuria (urolithiasis), dysuria (UTI) [1]
- Important negatives: Last menstrual period, possibility of pregnancy, prior episodes, recent travel, sick contacts, recent antibiotics
2. Alarm Features
- Hemodynamic instability (tachycardia, hypotension) → resuscitate first, consider hemorrhage (ruptured AAA, ectopic pregnancy, GI bleed) [1]
- Peritoneal signs: Rebound tenderness, involuntary guarding, rigidity → perforation, peritonitis [1]
- Pain out of proportion to exam → mesenteric ischemia until proven otherwise [7]
- Pulsatile abdominal mass → ruptured AAA (sensitivity of palpation only 47% for rAAA) [8-9]
- Absent bowel sounds → mesenteric ischemia or strangulated SBO [1]
- Fever + jaundice + RUQ pain (Charcot's triad) → ascending cholangitis
- Elderly/immunocompromised patients often have subtle or atypical presentations with higher morbidity [1]
3. Medications
- Relevant contributors: NSAIDs and aspirin increase risk of PUD and GI bleeding; NSAID-induced ulcers are more likely to be asymptomatic and present with perforation or hemorrhage. Corticosteroids mask peritoneal signs. Anticoagulants increase hemorrhagic risk [6]
- ED analgesics: Early analgesia is safe and does not alter diagnostic accuracy [3]
- First-line: IV acetaminophen 1 g or ketorolac 15–30 mg IV [10]
- Opioids: Morphine or hydromorphone in modest doses; do not withhold pending surgical evaluation [3]
- Adjuncts: Sub-dissociative ketamine (0.1–0.3 mg/kg IV), IV lidocaine for renal colic [10]
- Droperidol 2.5 mg IV reduces opioid requirements for undifferentiated abdominal pain [11]
- Antiemetics: Ondansetron 4 mg IV, metoclopramide 10 mg IV [12]
- Contraindicated: Avoid NSAIDs if suspected GI bleed, renal insufficiency, or heart failure [10]
4. Diet
- NPO if surgical pathology suspected or imaging with contrast planned
- Fatty food intake is a classic trigger for biliary colic [13]
- Alcohol → pancreatitis, gastritis
- High-fiber diet for chronic diverticular disease prevention (long-term)
- Clear liquid diet for mild gastroenteritis with advancement as tolerated
5. Review of Systems
- GI: Nausea, vomiting (bilious?), diarrhea (bloody?), constipation, obstipation, hematemesis, melena, hematochezia
- GU: Dysuria, frequency, hematuria, vaginal discharge/bleeding, testicular pain
- Cardiovascular: Chest pain, palpitations (atrial fibrillation → mesenteric embolism), claudication
- Pulmonary: Cough, pleuritic pain (lower lobe pneumonia can mimic abdominal pain — 10% of elderly patients with abdominal pain have a respiratory cause) [1]
- Constitutional: Fever, weight loss, night sweats
6. Collateral History and Family History
- Collateral from family/EMS: Witnessed syncope, duration of symptoms, medication compliance, recent procedures
- Family history: AAA (first-degree relatives), IBD, colon cancer, familial Mediterranean fever, hereditary pancreatitis
- Social context: Alcohol use (pancreatitis, hepatitis), IV drug use (endocarditis with septic emboli), sexual history (PID, ectopic pregnancy), recent travel (infectious etiologies)
7. Risk Factors
- Appendicitis: Age 10–30, male sex [5]
- Cholecystitis: Female sex, age >40, obesity, rapid weight loss, pregnancy [13]
- Diverticulitis: Age >65, low-fiber diet, obesity [1]
- Mesenteric ischemia: Age >60, atrial fibrillation, atherosclerotic disease, heart failure, hypercoagulable states, recent MI [14-15]
- Ruptured AAA: Male, age >65, smoking history, family history, known AAA [9]
- Ectopic pregnancy: Prior ectopic, PID, IUD, tubal surgery
- PUD: H. pylori infection, NSAID use, smoking, alcohol [6]
- SBO: Prior abdominal surgery (adhesions), hernias, Crohn disease, malignancy [1]
8. Differential Diagnosis
Common diagnoses
- Gastroenteritis — acute onset diarrhea, vomiting, diffuse crampy pain, sick contacts
- Nonspecific/functional abdominal pain — diagnosis of exclusion
- Biliary colic/cholecystitis — RUQ pain, postprandial, Murphy sign (LR+ 11.5–21.3) [13]
- Urolithiasis — colicky flank pain radiating to groin, hematuria
- Diverticulitis — LLQ pain, fever, change in bowel habits (clinical PPV up to 65%) [1]
- Appendicitis — periumbilical → RLQ migration, anorexia, low-grade fever [5]
- PUD/gastritis — epigastric burning, worse with fasting (duodenal) or eating (gastric) [6]
- UTI/pyelonephritis — dysuria, frequency, CVA tenderness
- Constipation — common, especially in elderly and pediatric populations
Cannot-miss diagnoses
- Ruptured AAA — classic triad of sudden abdominal/back pain, hypotension, pulsatile mass (full triad present in minority) [8-9]
- Mesenteric ischemia — pain out of proportion to exam, atrial fibrillation, elevated lactate; mortality 60–80% if delayed [14][16]
- Perforated viscus — sudden severe pain, rigid abdomen, free air on imaging [3]
- Bowel obstruction with strangulation — obstipation, distension, absent bowel sounds [1]
- Ectopic pregnancy — any reproductive-age patient with abdominal pain needs a pregnancy test [5]
- Ovarian/testicular torsion — acute onset, time-sensitive (6-hour window)
9. Past Medical History
- Prior abdominal surgeries (adhesive SBO risk) [1]
- Previous episodes of similar pain and prior workup
- Known gallstones, kidney stones, AAA, IBD, diverticular disease
- Cardiac history (atrial fibrillation → mesenteric embolism) [15]
- Immunosuppression (atypical presentations, opportunistic infections)
References
1. Acute Abdominal Pain in Adults: Evaluation and Diagnosis. — Yew KS, George MK, Allred HB. American Family Physician. 2023.
2. The Acute Abdomen: Structured Diagnosis and Treatment. — Börner N, Kappenberger AS, Weber S, et al. Deutsches Arzteblatt International. 2025.
3. Acute Abdomen in the Modern Era. — Rogers SO, Kirton OC. The New England Journal of Medicine. 2024.
4. Evaluation of Acute Abdominal Pain in Adults. — Cartwright SL, Knudson MP. American Family Physician. 2008.
5. Diagnosis and Management of Acute Appendicitis in Adults: A Review. — Moris D, Paulson EK, Pappas TN. The Journal of the American Medical Association. 2021.
6. Peptic Ulcer Disease: A Review. — Vakil N. The Journal of the American Medical Association. 2024.
7. Acute Mesenteric Ischemia: Updated Guidelines of the World Society of Emergency Surgery. — Bala M, Catena F, Kashuk J, et al. World Journal of Emergency Surgery : WJES. 2022.
8. Accuracy of Presenting Symptoms, Physical Examination, and Imaging for Diagnosis of Ruptured Abdominal Aortic Aneurysm: Systematic Review and Meta-Analysis. — Fernando SM, Tran A, Cheng W, et al. Academic Emergency Medicine : Official Journal of the Society for Academic Emergency Medicine. 2022.
9. Abdominal Aortic Aneurysm. — Haque K, Bhargava P. American Family Physician. 2022.
10. Optimizing the Treatment of Acute Pain in the Emergency Department. — American College of Emergency Physicians (2018). 2018.
11. DRopEridol for Abdominal Pain in the Emergency Department for Morphine Equivalent Reduction. The DREAMER Study. — Townsend BR, Malka ST, Di Paola SG, Nisly AE, Gilbert BW. The American Journal of Emergency Medicine. 2025.
12. Prophylactic Antiemetics for Adults Receiving Intravenous Opioids in the Acute Care Setting. — Gottlieb M, Carlson JN, Peksa GD. The Cochrane Database of Systematic Reviews. 2022.
13. Gallstone Disease: Common Questions and Answers. — Patel H, Jepsen J. American Family Physician. 2024.
14. High Risk and Low Prevalence Diseases: Mesenteric Ischemia. — Molyneux K, Beck-Esmay J, Koyfman A, Long B. The American Journal of Emergency Medicine. 2023.
15. Mesenteric Ischemia. — Clair DG, Beach JM. The New England Journal of Medicine. 2016.
16. Gastrointestinal Surgical Emergencies Textbook. — Ashley E. Aaron, Andrea Amabile, Ciro Andolfi, et al American College of Surgeons (2021). 2021.