Red flags
- Pain out of proportion to examination findings - mesenteric ischaemia
- Peritonism (guarding, rebound, rigidity) - surgical abdomen
- Haemodynamic instability - ruptured AAA, ectopic pregnancy, perforation
- Pain radiating to the back + hypotension in an older adult - ruptured AAA until excluded
- New severe pain in pregnancy/possible pregnancy - ectopic until excluded (beta-hCG in every woman of childbearing age with abdominal pain)
- Testicular pain with abdominal pain in a young male - torsion, time-critical
Differential by mechanism
By location (classic, but overlap is common)
- RUQ: biliary colic/cholecystitis, hepatitis, right lower lobe pneumonia
- Epigastric: peptic ulcer, pancreatitis, MI (esp. inferior)
- RIF: appendicitis, ectopic, ovarian pathology, Meckel's, caecal pathology
- LIF: diverticulitis, ovarian pathology, constipation
- Central/generalised: bowel obstruction, mesenteric ischaemia, early appendicitis, gastroenteritis, DKA, peritonitis
By mechanism
- Vascular: mesenteric ischaemia, ruptured AAA, splenic infarct
- Obstructive: bowel obstruction, biliary colic, renal colic
- Inflammatory/infective: appendicitis, diverticulitis, PID, cholecystitis, pancreatitis
- Referred/extra-abdominal: MI, pneumonia, DKA, testicular torsion, Addisonian crisis
- Gynaecological: ectopic pregnancy, ovarian torsion/cyst rupture, PID
Focused history
- Onset (sudden = vascular/perforation/torsion; gradual = inflammatory), character, radiation, associated symptoms (vomiting, bowel habit, urinary, gynaecological)
- LMP/pregnancy possibility, sexual history if PID/ectopic considered
- Vascular risk factors (AF, atherosclerosis) if mesenteric ischaemia considered
- Prior surgery (adhesions), similar previous episodes
Focused examination
- Vital signs first - haemodynamic instability changes urgency immediately
- Inspection, palpation (tenderness, guarding, rebound, masses, pulsatile mass), percussion, auscultation (bowel sounds - absent in ileus/late obstruction, tinkling in obstruction)
- Hernial orifices, testicular exam in males, pelvic exam if gynaecological cause considered
Investigation strategy
- Beta-hCG in every woman of childbearing age
- FBE, UEC, LFT, lipase, CRP, lactate (mesenteric ischaemia, generalised peritonitis)
- Urinalysis, erect CXR (free air), CT abdomen/pelvis with contrast for most undifferentiated significant pain
- Ultrasound for biliary/gynaecological/renal pathology; CT angiography if mesenteric ischaemia suspected
Management
- Haemodynamic resuscitation first if unstable, urgent surgical/gynaecological/vascular referral as indicated by the working diagnosis
- Analgesia should not be withheld pending diagnosis (does not mask peritonism or delay diagnosis - historic teaching now reversed)
- Source-specific management (antibiotics + appendicectomy, ERCP/cholecystectomy, IV fluids + bowel rest for obstruction, urgent laparotomy for perforation/ischaemia/ruptured AAA)
- Serial re-examination is often more informative than a single snapshot assessment in evolving/equivocal presentations
Traps
- Pain out of proportion to examination is the classic and frequently missed sign of mesenteric ischaemia
- Withholding analgesia "to avoid masking the exam" delays care without benefit - give analgesia
- A normal early lactate does not exclude mesenteric ischaemia - it rises late
- Beta-hCG is skipped more often than it should be in women with abdominal pain of any age post-menarche
Talk track
- "Vital signs and a pregnancy test come before I even start formulating a differential."
- "Pain out of proportion to the exam is ischaemia until I've actively excluded it."
8 of 8 sections written · drafted 2026-09-13