Abdominal pain

At a glance

• Most acute abdominal pain in adults is non-specific or from a handful of common causes: appendicitis, biliary disease, renal colic, diverticulitis, bowel obstruction and gastroenteritis.
• The physician's job is to spot the surgical abdomen, the vascular catastrophes (ruptured AAA, mesenteric ischaemia) and the medical mimics (DKA, inferior MI, lower lobe pneumonia, hypercalcaemia).
• Older, immunosuppressed and diabetic patients can have perforation or ischaemia with little tenderness, fever or leucocytosis.
• Give analgesia early. Opioids don't impair diagnostic accuracy.

Causes

Site	Common	Must not miss
Right upper quadrant	Biliary colic, cholecystitis, hepatitis	Cholangitis, liver abscess, right lower lobe pneumonia
Epigastric	Dyspepsia, peptic ulcer, pancreatitis	Inferior MI, perforated ulcer, ruptured AAA
Left upper quadrant	Gastritis	Splenic rupture (after EBV or trauma), splenic infarct
Periumbilical	Early appendicitis, gastroenteritis, small bowel obstruction	Mesenteric ischaemia, AAA
Right iliac fossa	Appendicitis, Crohn's ileitis, ovarian cyst	Ectopic pregnancy, ovarian torsion
Left iliac fossa	Diverticulitis, constipation	Colonic perforation, ischaemic colitis
Loin to groin	Renal colic, pyelonephritis	Leaking AAA mimicking renal colic in an older man
Diffuse	Gastroenteritis, IBS	Peritonitis, obstruction, mesenteric ischaemia

Medical causes to check in every unexplained case:

• Metabolic: DKA, hypercalcaemia, adrenal crisis, uraemia.
• Toxic and inherited: acute intermittent porphyria, lead poisoning, opioid withdrawal, cannabinoid hyperemesis syndrome (relief from hot showers).
• Inflammatory: familial Mediterranean fever, IgA vasculitis, polyarteritis nodosa, SLE serositis, hereditary angioedema (low C4 between attacks).
• Referred: inferior MI, pneumonia, herpes zoster before the rash, testicular torsion.
• Infection in Australian context: Strongyloides hyperinfection after steroids in people from endemic areas, including some remote Aboriginal communities.

Focused history

• Onset: sudden and maximal at onset suggests perforation, rupture, torsion or embolus. Gradual build suggests inflammation.
• Character: colicky (obstruction, ureter, biliary) versus constant (peritonitis, ischaemia). "Biliary colic" is usually constant for 30 minutes to hours.
• Migration: periumbilical pain moving to the right iliac fossa is the most useful historical feature of appendicitis.
• Associated features: vomiting before pain points to a medical cause; pain before vomiting to a surgical one. Absolute constipation with distension means obstruction.
• Vascular risk: AF, recent MI, heart failure, vasculopathy, prior postprandial pain and weight loss ("food fear" in chronic mesenteric ischaemia).
• Drugs: NSAIDs (ulcer), anticoagulants (rectus sheath or retroperitoneal haematoma), steroids (masked signs), opioids, SGLT2 inhibitors (euglycaemic DKA), GLP-1 receptor agonists (gallstones, pancreatitis).
• Gynaecological: last menstrual period, contraception, discharge, sexual history.

Focused examination

• Vital signs and shock index. Tachycardia may be the only sign of an intra-abdominal catastrophe; beta-blockers hide it.
• Peritonism: guarding, rigidity, pain on coughing or percussion. Rebound adds little.
• Pain out of proportion to tenderness is mesenteric ischaemia until proven otherwise.
• Murphy sign for cholecystitis. A palpable pulsatile mass for AAA. Hernial orifices and scars.
• Carnett sign: tenderness that increases when the patient lifts the head and tenses the abdominal wall points to abdominal wall pain.
• Genitalia, rectal examination where relevant, chest, and skin (zoster, purpura).

Red flags

• Haemodynamic instability, lactate over 2 mmol/L, or peritonism.
• Pain out of proportion to the findings, especially with AF.
• Age over 65 with new severe pain: CT threshold should be low.
• Pregnancy, possible ectopic, or a positive hCG with pain.
• Fever, jaundice and RUQ pain (Charcot triad) for cholangitis.
• Known AAA, or an older man with "renal colic" and no haematuria.

Investigations

• Bloods: FBC, electrolytes, creatinine, LFTs, lipase, CRP, glucose and ketones, calcium, venous gas with lactate.
• Beta-hCG in every woman who could be pregnant.
• Urinalysis. Haematuria is common in renal colic but also occurs in appendicitis and AAA.
• ECG and troponin for upper abdominal pain with cardiac risk.
• Lipase over 3 times the upper limit supports pancreatitis (see Acute pancreatitis).

Question	First imaging
Biliary disease, RUQ pain	Ultrasound
Undifferentiated acute abdomen in an adult	CT abdomen and pelvis with IV contrast
Mesenteric ischaemia or AAA (stable)	CT angiography
Unstable, suspected ruptured AAA	Bedside ultrasound, then straight to theatre
Pregnancy	Ultrasound, then MRI without gadolinium
Young adult, suspected appendicitis	Ultrasound first, CT if equivocal
Free air	Erect chest X-ray is quick; CT is more sensitive

• Pitfall: lactate is normal early in mesenteric ischaemia and rises only once bowel infarcts. Don't wait for it.

Management

General

• Resuscitate, analgesia (IV opioids titrated), antiemetic, nil by mouth if surgery is possible, early surgical referral for peritonism or obstruction.
• Sepsis with a surgical source needs antibiotics within the hour and source control.

Specific conditions

• Appendicitis (WSES 2025): use a score (Adult Appendicitis Score or AIR score) plus imaging to cut negative appendicectomy. Laparoscopic appendicectomy is standard and can wait up to 24 hours in uncomplicated disease. Antibiotics alone suit selected uncomplicated cases without an appendicolith (CODA). After non-operative treatment of an appendiceal abscess, follow up to exclude a neoplasm; WSES 2020 suggested colonoscopy and interval contrast-enhanced CT from age 40.
• Acute mesenteric ischaemia (WSES 2022): causes are arterial embolus (often AF; about a quarter to a half of cases) and arterial thrombosis (about 15 to 40%, rising in recent series), non-occlusive ischaemia (low flow, vasopressors, dialysis) and venous thrombosis. Give IV heparin, fluids and broad-spectrum antibiotics, then revascularise (endovascular or open) and resect dead bowel. Mortality is about 50% (30 to 70% when diagnosis is delayed), and falls with early diagnosis and revascularisation.
• Acute cholecystitis: antibiotics and early laparoscopic cholecystectomy, ideally within 72 hours and certainly in the same admission.
• Cholangitis (Tokyo 2018): antibiotics and biliary drainage, with timing set by severity. Grade III (organ dysfunction) needs urgent drainage once stabilised.
• Diverticulitis: CT confirms and grades it. Uncomplicated disease in an immunocompetent patient can be managed without antibiotics (DIABOLO and AVOD trials). Colonoscopy after recovery if not recently done or after a complicated episode.
• Adhesive small bowel obstruction: drip and suck, water-soluble contrast challenge, and surgery for strangulation or failure to resolve. Large bowel obstruction is cancer or volvulus until proven otherwise.
• Upper GI bleeding and perforated ulcer are covered in Gastrointestinal bleeding.

Chronic or recurrent abdominal pain

• Disorders of gut-brain interaction (IBS, functional dyspepsia) are the commonest causes. Make a positive diagnosis rather than repeating scans.
• Abdominal wall pain (positive Carnett sign): trigger point local anaesthetic.
• Chronic mesenteric ischaemia: postprandial pain, weight loss and food fear, usually with two or three diseased mesenteric vessels. CT angiography and revascularisation.
• Narcotic bowel syndrome: pain that worsens with escalating opioids. Wean the opioid.
• Recurrent attacks with normal imaging: porphyria, hereditary angioedema, familial Mediterranean fever, lead.

Special populations

• Older people: atypical presentations, higher rates of mesenteric ischaemia, AAA, diverticulitis and cancer, and mortality several times higher. Image early.
• Pregnancy: appendicitis is the commonest non-obstetric surgical emergency, and the appendix moves up with the uterus. Consider HELLP, acute fatty liver of pregnancy and placental abruption.
• Immunosuppressed: steroids blunt peritonism. Consider CMV colitis, neutropenic enterocolitis and Strongyloides.
• Rural and remote: a stable patient with suspected AAA, mesenteric ischaemia or peritonitis needs early retrieval to a centre with CT, vascular surgery and interventional radiology.

Pitfalls

• Pitfall: labelling an older man with flank pain and no haematuria as renal colic. Exclude AAA.
• Pitfall: reassurance from a soft abdomen in a patient on high-dose steroids or with severe pain in AF.
• Missing DKA (including euglycaemic DKA on an SGLT2 inhibitor), which commonly causes abdominal pain and vomiting.
• Forgetting beta-hCG before CT in a woman of reproductive age.
• A normal white cell count and CRP don't exclude appendicitis early in the illness.