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."
Study aid only. These notes are written with the help of AI. Not for guiding clinical decisions.