Acute abdominal pain: workup and approach
Acute abdominal pain in an adult. Identify the unstable patient and the surgical abdomen first, then use location, history and targeted tests to narrow the cause. Older adults and immunosuppressed patients often have serious disease with few signs.
Presenting complaint
Adult · US guidelines
Draft · awaiting physician review
01Orient
What's new in the evidence
- CODA (2020): for appendicitis, antibiotics were noninferior to appendectomy for 30-day health status, but about 3 in 10 needed appendectomy by 90 days (more with an appendicolith)
- Diverticulitis: ACP 2022 and ACG 2026 support outpatient care and selective (not routine) antibiotics for uncomplicated disease in immunocompetent patients
- Older adults and immunosuppressed patients often lack fever, guarding or leukocytosis; image early (CT with IV contrast)
Differential diagnoses
- Ruptured abdominal aortic aneurysm (can't miss)
- Mesenteric ischemia: pain out of proportion to exam (can't miss)
- Perforated viscus (can't miss)
- Ectopic pregnancy (can't miss)
- Bowel obstruction, volvulus
- Appendicitis, cholecystitis, cholangitis, diverticulitis, pancreatitis
- Nephrolithiasis, pyelonephritis
- Extra-abdominal: inferior MI, DKA, pneumonia, testicular or ovarian torsion
02Assess
Risk scores and decision tools
- Alvarado or AIR score for appendicitis
- Tokyo Guidelines for cholecystitis and cholangitis
- BISAP for pancreatitis
- Lactate (normal early in mesenteric ischemia)
Key history questions
- Onset (sudden suggests perforation, rupture or ischemia), location and migration of pain
- Vomiting, bowel and flatus, blood in stool
- Fever, jaundice, urinary symptoms
- Last menstrual period, pregnancy
- Prior surgery (adhesions), AF or vascular disease (ischemia), NSAIDs, alcohol
- Anticoagulants, immunosuppression
Examination findings
- Vital signs; appearance (still vs writhing)
- Peritonism: guarding, rigidity, rebound
- Distension, hernias, surgical scars
- Pulsatile mass, femoral pulses
- Murphy's sign, McBurney's point, CVA tenderness; pelvic or testicular exam as indicated
03Investigate
Initial investigations
- CBC, BMP, LFTs, lipase, lactate
- Urinalysis; pregnancy test in all who could be pregnant
- ECG in older adults or upper abdominal pain
- Bedside ultrasound: free fluid, aorta, gallbladder, hydronephrosis
Advanced investigations
- CT abdomen and pelvis with IV contrast for most undifferentiated severe pain
- Right upper quadrant ultrasound first for suspected biliary disease
- CT angiography for suspected mesenteric ischemia or AAA
- Pelvic ultrasound for gynecological causes
04Treat
Immediate management
- Unstable: resuscitate and call surgery while imaging is arranged
- Early analgesia (opioids as needed); it does not hide surgical diagnoses
- NPO, antiemetic, IV fluids
- Broad-spectrum antibiotics for peritonitis or sepsis
First-line treatment
- Treat the specific diagnosis
- NG decompression for bowel obstruction with vomiting
Second-line treatment
- Diagnostic laparoscopy when imaging is inconclusive and suspicion stays high
Specialist referrals
- General surgery for peritonitis, obstruction, appendicitis, cholecystitis
- Vascular surgery for AAA or mesenteric ischemia
- Gynecology for ectopic pregnancy or torsion
05Disposition
Admission criteria
- Peritonitis, sepsis, obstruction or a surgical diagnosis
- Older adults with undiagnosed severe pain
- Uncontrolled pain or vomiting
Safe discharge criteria
- Serious causes excluded, pain controlled, tolerating oral intake
- Clear return precautions and follow-up within 24–48 hours if undiagnosed
Follow-up timing
- Re-examination within 24–48 hours for undifferentiated pain
Patient instructions
- Return for worsening pain, fever, vomiting, blood in stool or fainting
Monitoring
- Serial abdominal exams
- Vital signs, lactate if ischemia possible
Clinical pearls and pitfalls
- Lactate can be normal early in mesenteric ischemia
- Up to 40% of ED abdominal pain is nonspecific; safety-netting matters
- Missed diagnoses are most often in older adults: lower your threshold for CT
RefGuidelines and landmark evidence
For education only. Typical adult starting points; confirm doses against renal function, allergies, interactions and your institution's protocols. Not a substitute for clinical judgment or senior review.