📋 Key Information Summary
- Acute vs chronic distinction: Acute abdominal pain (< 7 days) demands rapid triage for surgical emergencies; chronic/recurrent pain (> 3 months) follows a structured diagnostic model emphasising pattern recognition, red flags, and the seven masquerades.
- Diagnostic quadrant model: Systematic approach dividing the abdomen into nine regions (right upper, epigastric, left upper, right flank, central/periumbilical, left flank, right iliac, suprapubic, left iliac) guides differential diagnosis efficiently.
- Red flags requiring urgent referral: Peritonism/peritonitis, haemodynamic instability, rigidity, rebound tenderness, absent bowel sounds, frank GI haemorrhage, suspected ectopic pregnancy, and acute mesenteric ischaemia — refer immediately to the ED or surgical team.
- Australian emergency incidence: Abdominal pain accounts for approximately 7–10% of all ED presentations nationally, with appendicitis, cholecystitis, and renal colic among the most common surgical causes.
- Vital signs first: Always assess airway, breathing, circulation, and pain severity (VAS/NRS) before focused history — haemodynamic instability mandates simultaneous resuscitation and investigation.
- Serious disorders not to miss: AAA rupture, mesenteric ischaemia, ectopic pregnancy, bowel obstruction, pancreatitis (severe), myocardial infarction (inferior), and testicular torsion.
- Seven masquerades of abdominal pain: Depression, diabetes (DKA/gastroparesis), drugs (NSAIDs, opioids, metformin), spinal pathology (referred pain), thyroid disease, UTI/pyelonephritis, and porphyria — always consider in chronic or unexplained presentations.
- Initial investigations in primary care: FBC, CRP/ESR, UEC, LFTs, lipase, urinalysis, urine hCG (all women of childbearing age), and plain abdominal X-ray when obstruction or perforation is suspected.
- CT abdomen/pelvis with IV contrast is the gold-standard imaging for most acute presentations when the diagnosis is uncertain; ultrasound is preferred for biliary, pelvic, and paediatric pathology.
- Analgesia does not mask peritonitis: Current evidence supports early adequate analgesia (IV morphine 0.1 mg/kg or fentanyl) — it does not impair clinical examination and improves patient cooperation.
- Aboriginal and Torres Strait Islander considerations: Higher rates of acute appendicitis, gallstone disease, and chronic liver disease; delayed presentation due to geographic remoteness and health system barriers; culturally safe communication is essential.
- Paediatric note: Intussusception (6–36 months), malrotation with volvulus (neonates), and testicular torsion must not be missed; ultrasonography is first-line paediatric imaging.
Introduction & Australian Epidemiology
Abdominal pain is one of the most common presenting complaints in Australian general practice and emergency departments. It accounts for approximately 7–10% of all emergency presentations and is a leading reason for specialist gastroenterology and surgical referral. The diagnostic challenge lies in the breadth of the differential diagnosis — ranging from benign, self-limiting conditions (e.g. viral gastroenteritis, functional dyspepsia) to life-threatening emergencies (e.g. ruptured abdominal aortic aneurysm, mesenteric ischaemia, ectopic pregnancy).
A structured approach is essential. This article presents a practical framework for the Australian clinician, distinguishing acute (onset < 7 days, often < 72 hours) from chronic or recurrent (> 3 months) abdominal pain, highlighting red flags that mandate urgent referral, and exploring the seven common masquerades that can mimic intra-abdominal pathology.
Australian Burden of Disease
- Abdominal pain is the most common presenting complaint in Australian general practice, representing ~5% of all encounters (BEACH study data, AIHW).
- Appendicectomy remains one of the most frequently performed emergency surgeries in Australia, with a lifetime risk of ~8%.
- Gallstone-related disease affects approximately 10–15% of Australian adults, with significantly higher prevalence among Aboriginal and Torres Strait Islander Australians and those with metabolic syndrome.
- Functional gastrointestinal disorders (IBS, functional dyspepsia) account for up to 40% of chronic abdominal pain referrals to gastroenterology outpatient clinics.
- Acute pancreatitis incidence in Australia is approximately 15–30 per 100,000 population per year, with alcohol and gallstones as the predominant aetiologies.
- Healthcare costs for abdominal pain presentations exceed .2 billion annually when accounting for ED admissions, surgical procedures, imaging, and specialist referrals (AIHW, 2023).
Clinical pearl: The history accounts for approximately 70% of the diagnostic accuracy in abdominal pain. A thorough, structured history — including pain character, location, radiation, aggravating/relieving factors, associated symptoms, and medication/substance use — is far more valuable than a battery of unselected investigations.
Acute Abdominal Pain Diagnostic Model
The acute abdomen demands a rapid, systematic approach. The goal is to distinguish surgical emergencies from medical causes that can be managed non-operatively, while identifying the small percentage of patients who require immediate intervention.
Step 1: Rapid Assessment (ABCDE + Pain Score)
1
Airway & Breathing
Assess respiratory rate, oxygen saturation. Kussmaul breathing may indicate metabolic acidosis (DKA, lactic acidosis from mesenteric ischaemia).
2
Circulation
HR, BP, capillary refill, skin colour. Tachycardia + hypotension = haemorrhagic or septic shock — activate emergency response. Two large-bore IV cannulae, fluid resuscitation.
3
Disability
GCS, blood glucose, pupillary response. Altered consciousness in abdominal pain suggests severe sepsis, metabolic derangement, or AAA rupture.
4
Exposure & Pain Score
Full abdominal exposure, NRS 0–10 pain assessment. Document tenderness, guarding, rigidity, distension, bowel sounds, PR examination if indicated.
Step 2: Quadrant-Based Differential Diagnosis
| Abdominal Region | Common Causes | Key Investigation |
|---|---|---|
| Right upper quadrant (RUQ) | Cholecystitis, cholangitis, hepatitis, hepatic abscess, right lower lobe pneumonia | RUQ USS, LFTs, lipase, FBC |
| Epigastric | Peptic ulcer disease, gastritis, pancreatitis, MI (inferior), aortic dissection | ECG, lipase, troponin, FBE; consider endoscopy |
| Left upper quadrant (LUQ) | Splenic pathology (rupture, infarct), gastritis, pancreatitis (body/tail), splenic flexure syndrome | CT abdomen, FBC, lipase |
| Right flank | Ureteric colic (right), pyelonephritis, renal cell carcinoma | Urinalysis, CT KUB (non-contrast for stones) |
| Central / Periumbilical | Small bowel obstruction, early appendicitis, mesenteric ischaemia, AAA, pancreatitis | CT abdomen with contrast, lactate, CT angiography if ischaemia suspected |
| Left flank | Ureteric colic (left), pyelonephritis, diverticulitis (rare) | Urinalysis, CT KUB, FBC/CRP |
| Right iliac fossa (RIF) | Appendicitis, ectopic pregnancy, ovarian torsion/cyst, Crohn's (terminal ileum), mesenteric lymphadenitis, psoas abscess | FBC, CRP, USS, urine hCG, CT if equivocal |
| Suprapubic / Pelvic | UTI, urinary retention, ectopic pregnancy, pelvic inflammatory disease, ovarian pathology, testicular torsion | Urinalysis, urine hCG, pelvic USS, swabs if PID |
| Left iliac fossa (LIF) | Diverticulitis, ectopic pregnancy, ovarian pathology, sigmoid volvulus, IBD flare | CT abdomen/pelvis, FBC, CRP, urine hCG |
| Diffuse / Generalised | Peritonitis, bowel obstruction, mesenteric ischaemia, gastroenteritis, metabolic (DKA, uraemia, Addisonian crisis), familial Mediterranean fever | CT abdomen, lactate, VBG, UEC, amylase/lipase |
Step 3: History — The SOCRATES Mnemonic
| Element | Details to Elicit | Diagnostic Significance |
|---|---|---|
| Site | Precise location, radiation | RIF → appendicitis; shoulder tip → diaphragmatic irritation (ruptured ectopic, splenic rupture) |
| Onset | Sudden vs gradual; timing | Sudden ("thunderclap") → perforation, AAA rupture, mesenteric ischaema; gradual → inflammatory/infectious |
| Character | Colicky, burning, tearing, dull, aching | Colicky → hollow viscus obstruction (renal colic, biliary colic, SBO); tearing → vascular catastrophe |
| Radiation | Back, shoulder, groin, scrotum | Back → pancreatitis, AAA; groin/scrotum → renal colic; shoulder → diaphragmatic irritation |
| Associations | Nausea, vomiting, fever, dysuria, melaena, change in bowel habit | Fever + RIF pain → appendicitis; jaundice + RUQ pain → cholangitis |
| Time course | Duration, constant vs intermittent, worsening | Constantly worsening → surgical cause; intermittent/chronic → functional or inflammatory |
| Exacerbating / Relieving | Movement, food, position, defecation | Worse with movement → peritonitis; relieved by defecation → IBS; worse after fatty food → biliary |
| Severity | NRS 0–10 | ≥ 7/10 with systemic signs → high acuity; consider urgent imaging |
Step 4: Physical Examination — Systematic Approach
- Inspection: Distension, visible peristalsis (SBO), surgical scars (adhesions), hernia orifices, Grey Turner's sign (flank ecchymosis — retroperitoneal haemorrhage), Cullen's sign (periumbilical ecchymosis — intraperitoneal haemorrhage).
- Auscultation: High-pitched tinkering bowel sounds (obstruction); absent bowel sounds (peritonitis, ileus).
- Percussion: Tympany (distension/obstruction), dullness (mass, ascites), percussion tenderness (peritonitis).
- Palpation: Begin away from the site of maximum pain. Assess for guarding (voluntary vs involuntary — involuntary rigidity is a peritoneal sign), rebound tenderness, rigidity, palpable masses, organomegaly, aortic pulsation (expansile = AAA until proven otherwise).
- Special signs: Rovsing's (RIF pain on LIF pressure — appendicitis), Murphy's (arrest of inspiration during RUQ palpation — cholecystitis), McBurney's point tenderness (appendicitis), psoas sign (retrocaecal appendicitis), obturator sign (pelvic appendicitis).
- Digital rectal examination: Melaena, faecal impaction, pelvic tenderness (appendicitis/pelvic abscess), prostate pathology.
- Pelvic examination (when indicated): Cervical motion tenderness (PID), adnexal masses/tenderness (ectopic, ovarian torsion).
Evidence update: Analgesia given before surgical assessment does NOT mask peritonitis or delay diagnosis (Level I evidence, multiple RCTs). Adequate analgesia (IV morphine or fentanyl) improves examination accuracy and patient cooperation. Do not withhold analgesia while awaiting surgical review.
Step 5: Initial Investigations — Primary Care & ED
Select investigations based on clinical suspicion rather than ordering a standard "abdominal pain panel":
Essential
FBC (full blood count)
Leucocytosis (infection/inflammation), anaemia (haemorrhage), thrombocytopenia (sepsis/DIC)
Essential
CRP / ESR
Inflammatory markers; CRP > 50 mg/L raises concern for surgical/infectious cause
Essential
UEC (urea, electrolytes, creatinine)
Dehydration, renal impairment, electrolyte derangement (vomiting, obstruction)
Essential
LFTs (liver function tests)
Hepatitis, cholecystitis, cholangitis — ALT/AST, ALP, GGT, bilirubin
Essential
Serum lipase
Pancreatitis (lipase > 3× ULN is diagnostic; more specific than amylase)
Essential
Urine hCG (β-hCG)
All women of childbearing age — ectopic pregnancy must be excluded before imaging/analgesia planning
Available
Urinalysis / Urine MCS
UTI, pyelonephritis, haematuria (renal colic, malignancy)
Available
Venous blood gas (VBG)
Lactate (> 2 mmol/L — ischaemia/sepsis), pH (metabolic acidosis), glucose (DKA)
Available
Plain abdominal X-ray (AXR)
Obstruction (air-fluid levels, dilated loops), perforation (free air), faecal loading, toxic megacolon
Referral / ED
CT abdomen/pelvis with IV contrast
Gold standard for acute abdomen when diagnosis uncertain. MBS item 56108. Sensitivity > 90% for appendicitis, diverticulitis, obstruction.
Available
Abdominal ultrasound (RUQ / pelvic)
First-line for biliary pathology, pelvic masses, paediatric abdomen. No ionising radiation.
Specialist
CT angiography / mesenteric duplex
Suspected acute mesenteric ischaemia — lactate + CT angiography is the standard diagnostic pathway.
Chronic / Recurrent Abdominal Pain
Chronic abdominal pain — defined as pain persisting or recurring for ≥ 3 months — is extremely common in Australian general practice. The Rome IV criteria provide a structured diagnostic framework for functional gastrointestinal disorders, which account for a large proportion of chronic presentations. However, clinicians must always exclude organic disease before diagnosing a functional disorder, particularly in patients with new-onset symptoms after age 50.
Diagnostic Approach to Chronic Abdominal Pain
1
Characterise the Pain Pattern
Use SOCRATES. Map the pain to meals, bowel actions, menstrual cycle, stress, posture, and medications. Document functional impact on work, sleep, and daily activities.
2
Identify Red Flags
Weight loss > 5%, dysphagia, persistent vomiting, GI bleeding, iron deficiency anaemia, nocturnal symptoms waking from sleep, family history of GI malignancy, age > 50 with new symptoms, palpable mass.
3
Tier-1 Investigations (Primary Care)
FBC, CRP, UEC, LFTs, lipase, coeliac serology (anti-tTG IgA + total IgA), faecal calprotectin, urine hCG, urinalysis. Consider iron studies and TFTs.
4
Consider Functional Disorders (Rome IV)
IBS (abdominal pain ≥ 1 day/week associated with defecation, change in stool frequency/form), functional dyspepsia (epigastric pain/burning, early satiety, postprandial fullness). Diagnose by positive criteria, not solely by exclusion.
5
Tier-2 Investigations (Specialist)
Gastroscopy, colonoscopy, CT/MR enterography, gastric emptying study, breath testing (H₂/CH₄ for SIBO, lactose/fructose malabsorption), MRCP for biliary pain.
Common Causes of Chronic / Recurrent Abdominal Pain
| Category | Condition | Key Features | Initial Workup |
|---|---|---|---|
| Functional | Irritable bowel syndrome (IBS) | Pain with defecation, altered bowel habit, bloating; Rome IV criteria; onset ≥ 6 months ago | FBC, CRP, coeliac serology, faecal calprotectin — all normal |
| Functional | Functional dyspepsia | Epigastric pain/burning, early satiety, postprandial fullness; Rome IV criteria | FBC, LFTs, lipase; consider H. pylori test-and-treat; gastroscopy if alarm features |
| Inflammatory | Inflammatory bowel disease (Crohn's, UC) | Diarrhoea (often bloody in UC), weight loss, perianal disease (Crohn's), raised CRP/faecal calprotectin | Faecal calprotectin (≥ 250 μg/g = high probability), CRP, colonoscopy with biopsies |
| Structural | Adhesive small bowel obstruction | Prior abdominal surgery, colicky periumbilical pain, distension, vomiting, constipation | AXR (air-fluid levels), CT abdomen if incomplete/subacute |
| Metabolic | Coeliac disease | Chronic bloating, diarrhoea, fatigue, iron deficiency; HLA-DQ2/DQ8 associated | Anti-tTG IgA + total IgA (screen); duodenal biopsy (confirm) |
| Infectious | H. pylori gastritis | Epigastric pain, nausea, early satiety; linked to peptic ulcer and gastric MALT lymphoma | Urea breath test (UBT) or stool antigen; stool H. pylori antigen (MBS item 69506) |
| Biliary | Biliary colic / Functional gallbladder disorder | Episodic RUQ pain (30 min–hours), often post-prandial, normal LFTs and ultrasound between episodes | RUQ USS, LFTs, lipase; HIDA scan with ejection fraction if USS normal and recurrent |
| Gynaecological | Endometriosis | Cyclical pelvic pain, dysmenorrhoea, dyspareunia, dyschezia; often delayed diagnosis (avg 7 years) | Pelvic USS (endometrioma), MRI; diagnostic laparoscopy is gold standard |
| Vascular | Chronic mesenteric ischaemia | Post-prandial pain ("intestinal angina"), food aversion, weight loss; risk factors: smoking, PVD, AF | CT angiography, mesenteric duplex ultrasound |
| Neoplastic | Colorectal, gastric, or pancreatic cancer | Age > 50, weight loss, change in bowel habit, iron deficiency anaemia, jaundice (pancreatic) | CT abdomen/pelvis, colonoscopy, faecal immunochemical test (FIT) — National Bowel Cancer Screening Program |
Rome IV Diagnostic Criteria — Irritable Bowel Syndrome (IBS)
Recurrent abdominal pain on average ≥ 1 day/week in the last 3 months, associated with ≥ 2 of:
- Related to defecation
- Associated with a change in frequency of stool
- Associated with a change in form (appearance) of stool
Criteria fulfilled for the last 3 months with symptom onset ≥ 6 months before diagnosis.
IBS subtypes: IBS-C (constipation-predominant), IBS-D (diarrhoea-predominant), IBS-M (mixed), IBS-U (unsubtyped).
Red Flags & Serious Disorders Not to be Missed
Surgical emergencies requiring immediate referral: Peritonitis (generalised rigidity, rebound, absent bowel sounds), suspected perforation (sudden-onset severe pain with rigidity — "board-like" abdomen), haemodynamic instability, suspected ruptured AAA (pulsatile expansile mass + hypotension), testicular torsion (acute scrotal pain in adolescent/young adult), and acute mesenteric ischaemia (atrial fibrillation + acute severe pain out of proportion to examination findings).
Red Flag Symptoms & Signs
| Red Flag | Suggests | Action |
|---|---|---|
| Unintentional weight loss > 5% in 3 months | Malignancy, chronic infection, IBD | Urgent CT + colonoscopy/gastroscopy referral within 2 weeks |
| Progressive dysphagia | Oesophageal carcinoma, stricture | Urgent gastroscopy (2-week target) |
| Persistent vomiting without clear cause | Bowel obstruction, raised ICP, metabolic derangement | AXR, UEC, VBG; CT if concern for obstruction |
| GI bleeding (haematemesis, melaena, haematochezia) | Peptic ulcer, varices, colorectal cancer, diverticular bleed, ischaemic colitis | Haemodynamic resuscitation + urgent endoscopy; call surgical/medical registrar |
| Iron deficiency anaemia (new) | Colorectal cancer, coeliac disease, IBD, NSAID gastropathy | Coeliac serology, colonoscopy (age > 50 or family history), consider gastroscopy |
| Nocturnal pain waking from sleep | Organic disease (PUD, malignancy, IBD) — functional pain rarely wakes from sleep | Investigate — this symptom strongly points away from a functional cause |
| Palpable abdominal mass | Malignancy, AAA, abscess, Crohn's (terminal ileum) | Urgent CT abdomen/pelvis; vascular surgery if pulsatile mass |
| Age > 50 with new-onset abdominal pain | Higher risk of malignancy, AAA, mesenteric ischaemia, diverticular disease | Lower threshold for CT and endoscopic investigation |
| Family history of GI malignancy (especially CRC, FAP, Lynch) | Hereditary cancer syndromes | Genetic referral; colonoscopy surveillance as per guidelines (typically 5–10 years before youngest affected relative) |
| Abdominal pain in pregnancy + vaginal bleeding | Ectopic pregnancy, placental abruption, miscarriage | Urgent serum β-hCG, pelvic USS, G&H; emergency referral |
| Acute severe pain with AF or recent MI | Acute mesenteric ischaemia | Lactate, CT angiography, urgent surgical referral — mortality > 60% if delayed |
Serious Disorders Not to Miss — Summary
Life-Threatening
Must Not Miss
- Ruptured AAA
- Acute mesenteric ischaemia
- Perforated viscus
- Ectopic pregnancy (ruptured)
- Testicular torsion
- Acute pancreatitis (severe)
- Bowel obstruction (strangulated)
- Inferior MI (mimics epigastric pain)
Setting: Immediate ED referral / Emergency surgery
Urgent
Time-Sensitive Diagnosis
- Appendicitis (perforation risk increases after 36 h)
- Acute cholecystitis / cholangitis
- Diverticulitis (complicated)
- Ectopic pregnancy (unruptured)
- Ovarian torsion
- Necrotising enterocolitis (neonates)
- Intussusception (paediatric)
Setting: ED / Acute surgical unit, same-day assessment
Outpatient
Assess & Investigate
- Colorectal cancer screening (new red flags)
- IBD flare (mild–moderate)
- Coeliac disease
- H. pylori gastritis
- Chronic mesenteric ischaemia
- Endometriosis
Setting: GP urgent referral (2-week pathway) / Outpatient gastroenterology
Seven Masquerades & Psychogenic Considerations
The concept of the "seven masquerades" (adapted from Murtagh's General Practice) refers to systemic or extra-abdominal conditions that commonly present as abdominal pain but are frequently missed when clinicians focus narrowly on intra-abdominal pathology. These must be actively considered in every patient with chronic, recurrent, or unexplained abdominal pain.
The Seven Masquerades of Abdominal Pain
1. Depression & Somatisation
Functional somatic syndrome
Features
Chronic diffuse pain, multiple somatic complaints (headache, fatigue, musculoskeletal), poor sleep, anhedonia. Symptoms often worsen with stress. "Doctor shopping" and extensive negative workup.
Assessment
PHQ-9, GAD-7. Ask directly about mood, hopelessness, functional impairment. Explore illness beliefs.
Management
Validate symptoms ("the pain is real"). CBT, graded exercise, low-dose TCAs (amitriptyline 10–25 mg nocte) for functional pain. Mirtazapine 15 mg nocte if nausea/anorexia prominent. GP Mental Health Treatment Plan (Medicare item 2710/2712).
2. Diabetes Mellitus
DKA · Gastroparesis · Autonomic neuropathy
Features
DKA: abdominal pain + vomiting + Kussmaul breathing in known T1DM (may be the presenting feature of new T1DM). Gastroparesis: early satiety, nausea, bloating, postprandial fullness in long-standing DM.
Key test
Blood glucose, VBG (pH, ketones, bicarbonate). Gastric emptying study for gastroparesis.
Action
DKA = emergency (insulin infusion, fluid resuscitation). Gastroparesis: dietary modification, metoclopramide 10 mg TDS, domperidone 10 mg TDS (QTc caution), consider erythromycin 200 mg BD as prokinetic.
3. Drugs & Toxins
NSAIDs · Opioids · Metformin · Antibiotics · Alcohol
Common culprits
NSAIDs (gastritis, PUD, renal impairment), opioids (constipation, bowel obstruction), metformin (diarrhoea, lactic acidosis), colchicine, SSRIs (nausea), iron supplements, alcohol (gastritis, pancreatitis, hepatitis).
Action
Always review the medication chart. Deprescribing trial. Consider PPI cover if NSAIDs unavoidable. Opioid-induced constipation: macrogol, naloxegol (Movantik® — Authority Required PBS).
4. Spinal / Referred Pain
Thoracolumbar radiculopathy · Herpes zoster
Features
Pain that follows a dermatomal pattern (T10–L1), worsened by movement/spinal loading, may be accompanied by back pain. Herpes zoster: dermatomal pain preceding rash by 2–3 days. Viscero-somatic convergence: T10–L1 dermatomes overlap with abdominal organs.
Key test
Spinal examination, neurological assessment of lower limbs, skin inspection (vesicles in zoster). MRI spine if radiculopathy suspected.
Action
Gabapentin 300 mg OD titrated to 300 mg TDS; pregabalin 75 mg BD (Authority Required PBS). Zoster: valaciclovir 1 g TDS for 7 days (within 72 h of rash onset).
5. Thyroid Disease
Hypothyroidism · Hyperthyroidism
Features
Hypothyroidism: constipation, abdominal distension, ileus (severe — myxoedema ileus). Hyperthyroidism: hypermotility, diarrhoea, weight loss despite increased appetite.
Key test
TSH, free T4, free T3. MBS item 66716.
Action
Treat underlying thyroid disorder. Myxoedema ileus: IV levothyroxine + IV hydrocortisone in ICU setting.
6. UTI / Pyelonephritis
Urinary tract infection · Renal abscess
Features
Flank pain + fever + dysuria (classic triad of pyelonephritis). Suprapubic pain, frequency, urgency in lower UTI. In elderly/confused patients, UTI may present with abdominal pain and delirium as the sole features.
Key test
Urinalysis (nitrites, leucocytes, blood), urine MCS. FBC, CRP, UEC. USS if complicated or not responding to treatment (renal abscess, obstruction).
Treatment
Uncomplicated UTI: trimethoprim 300 mg PO nocte × 3 days (or nitrofurantoin 100 mg BD × 5 days). Pyelonephritis: ceftriaxone 1 g IV OD (inpatient) or ciprofloxacin 500 mg BD × 7 days (outpatient mild). Refer if septic.
7. Porphyria
Acute intermittent porphyria (AIP)
Features
Severe episodic abdominal pain (often colicky), nausea, vomiting, constipation, tachycardia, hypertension, neuropsychiatric symptoms (anxiety, confusion, seizures). Abdominal examination often benign relative to pain severity. Predominantly affects young women.
Key test
Urine porphobilinogen (PBG) during acute attack — sample must be protected from light. Random (spot) urine PBG is the initial screening test (sensitivity > 95% during attacks).
Action
Avoid precipitants (certain drugs — barbiturates, sulphonamides, anticonvulsants, oral contraceptives). Acute attack: IV haem arginate (Normosang®) 3 mg/kg/day × 4 days — specialist emergency treatment. Carbohydrate loading (IV glucose 10% if mild). Refer to metabolic medicine.
Psychogenic & Functional Considerations
Up to 40% of patients referred to gastroenterology for chronic abdominal pain have a functional disorder. The following principles apply:
- Validate the symptom: "The pain is real and distressing" — somatic symptom disorders are not "made up."
- Explore illness beliefs: "What do you think is causing this? What are you most worried about?" Often patients fear cancer or another serious diagnosis.
- Avoid iatrogenic harm: Repeated negative investigations reinforce health anxiety. Set clear investigation boundaries early. Use the phrase "We have done thorough tests to rule out the dangerous causes."
- Biopsychosocial formulation: Identify perpetuating factors — stress, sleep disturbance, avoidance behaviours, secondary gain, comorbid anxiety/depression.
- Multidisciplinary approach: GP, psychologist (CBT/ACT), dietitian (low FODMAP for IBS), physiotherapist (graded exercise). Use GP Mental Health Treatment Plan (Medicare items 2710/2712 — up to 10 sessions per calendar year).
- Pharmacotherapy for functional pain: Low-dose amitriptyline 10–25 mg nocte (first-line for IBS and functional dyspepsia), titrate to 50 mg. Dicyclomine 10–20 mg TDS PRN for cramping. Mebeverine 135 mg TDS (not PBS-listed in Australia; available as private script). Peppermint oil capsules (Colpermin®) 0.2 mL TDS before meals.
Important: Never assume abdominal pain is psychogenic without first completing appropriate investigations, especially in patients with red flags, age > 50 with new symptoms, or progressive symptoms. Functional is a diagnosis of positive criteria, not a diagnosis of exclusion alone.
Initial Management & Analgesia
Analgesia Ladder for Acute Abdominal Pain
Paracetamol
Panadol® · First-line analgesic
Adult dose
1 g PO/IV QID (max 4 g/day; 60 mg/kg/day if < 50 kg or hepatic impairment)
Paediatric dose
15 mg/kg PO/IV QID (max 60 mg/kg/day)
Renal adjustment
eGFR 10–50: max 1.5 g/day; eGFR < 10: max 1 g/day
PBS status
✔ PBS General Benefit (IV: Authority Required for inpatient use)
Ibuprofen
Nurofen® · Anti-inflammatory (use cautiously)
Adult dose
200–400 mg PO TDS with food (max 1.2 g/day OTC; 2.4 g/day prescription)
Paediatric dose
5–10 mg/kg PO TDS (max 30 mg/kg/day)
Contraindications
GI bleeding, renal impairment (eGFR < 30), active PUD, concurrent anticoagulants, third trimester pregnancy
PBS status
✔ PBS General Benefit
Morphine
MS Contin® · Opioid (moderate–severe pain)
Adult dose
IV: 0.1 mg/kg titrated (typically 2.5–5 mg IV q4h PRN). PO: 5–10 mg q4h PRN (immediate release). Modified release: 10–20 mg BD.
Paediatric dose
0.1–0.2 mg/kg IV q4h (use in specialist setting only)
Renal adjustment
eGFR 10–50: extend interval to q6–8h or reduce dose by 50%; eGFR < 10: avoid (active metabolite accumulation) — use fentanyl or hydromorphone
PBS status
⚠ PBS Authority Required
Fentanyl
Sublimaze® · Opioid (short-acting IV)
Adult dose
25–50 μg IV titrated (onset 1–2 min, duration 30–60 min). Ideal for procedural analgesia and renal impairment.
Renal adjustment
No dose adjustment required (preferred opioid in renal impairment)
PBS status
✔ PBS General Benefit (injection)
Ondansetron
Zofran® · Antiemetic
Adult dose
4 mg PO/IV/ODT q8h PRN (max 8 mg/dose)
Paediatric dose
0.1–0.15 mg/kg IV (max 4 mg); 2–4 mg PO depending on weight
Caution
Prolongs QTc — avoid in congenital long QT. Constipating — caution in suspected obstruction.
PBS status
✔ PBS General Benefit
Hyoscine butylbromide
Buscopan® · Antispasmodic
Adult dose
20 mg PO/IV TDS PRN (max 80 mg/day PO; 100 mg/day IV)
Indications
Smooth muscle spasm — biliary colic, renal colic (adjunct), bowel spasm in IBS. Avoid in suspected mechanical bowel obstruction.
PBS status
✔ PBS General Benefit
Disposition Decision — Primary Care
Refer to ED / Call Ambulance
- Haemodynamic instability (HR > 100, SBP < 90)
- Peritonism / generalised rigidity
- Suspected AAA (pulsatile expansile mass)
- Suspected ectopic pregnancy
- Frank GI haemorrhage (haemodynamic compromise)
- Severe pain (NRS ≥ 8) not responding to analgesia
- Signs of sepsis (temp > 38.5°C + tachycardia + hypotension)
- Acute abdomen of uncertain aetiology in immunocompromised patient
Manage in Primary Care
- Mild, self-limiting symptoms with no red flags
- Known IBS / functional dyspepsia flare
- Gastroenteritis with adequate hydration
- Constipation with faecal impaction (disimpaction, osmotic laxatives)
- UTI (uncomplicated) — empirical antibiotics pending MCS
- Musculoskeletal / abdominal wall pain
- Follow-up plan with safety netting ("return immediately if…")
Special Populations
Pregnancy
Always exclude ectopic pregnancy
Urine β-hCG in all women of childbearing age with abdominal pain. First trimester pain + bleeding = ectopic until proven otherwise (β-hCG discriminatory zone ~1,500–2,000 IU/L with TVS).
Appendicitis in pregnancy
Most common non-obstetric surgical emergency. RIF pain may present higher as the uterus enlarges. MRI is preferred imaging (no ionising radiation); USS if MRI unavailable.
Analgesia
Paracetamol safe in all trimesters. Avoid NSAIDs (especially 3rd trimester — premature ductus arteriosus closure). Codeine: avoid in 3rd trimester (neonatal respiratory depression). Morphine: use only when clearly indicated.
Pre-eclampsia / HELLP
Epigastric/RUQ pain in a pregnant woman > 20 weeks with hypertension = pre-eclampsia/HELLP until proven otherwise. Check BP, urinalysis (protein), LFTs, platelets. Obstetric emergency.
Paediatrics
Age-specific emergencies
Neonates: malrotation with volvulus (bilious vomiting = surgical emergency), necrotising enterocolitis (premature), Hirschsprung's enterocolitis. 6–36 months: intussusception (currant jelly stools, episodic screaming). 5–15 years: appendicitis (most common surgical cause).
Testicular torsion
Acute scrotal pain in males < 25 years — surgical emergency. Time-critical: viability decreases significantly after 6 hours. Do not wait for USS if clinical suspicion high — immediate surgical exploration.
Functional abdominal pain
Very common in school-age children (prevalence 10–15%). Rome IV paediatric criteria. Reassurance, dietary review, psychological support. Avoid excessive investigation if no red flags.
Imaging
Ultrasound is first-line (no radiation). Avoid CT in children unless absolutely necessary (ALARA principle — radiation dose 2–3× higher per unit body mass vs adults).
Elderly (≥ 65 years)
Atypical presentations
Elderly patients may present with minimal pain, absent fever, and vague symptoms. Afebrile appendicitis, painless perforation, and silent myocardial infarction are well documented. Maintain a low threshold for investigation.
Common serious causes
Diverticulitis, bowel obstruction (adhesions, hernias, colorectal cancer), AAA, mesenteric ischaemia, cholecystitis, and constipation/faecal impaction. Mortality from acute abdominal conditions is significantly higher in the elderly.
Polypharmacy
Review medications — NSAIDs (GI bleed risk), opioids (constipation/ileus), anticholinergics (ileus/urinary retention), anticoagulants (GI haemorrhage). Use the Beers Criteria to identify potentially inappropriate medications.
Analgesia
Start at 50% of standard adult doses. Avoid pethidine (normeperidine accumulation). Morphine: extend interval. Fentanyl preferred in renal impairment. Paracetamol: max 3 g/day (hepatic safety margin).
Renal Impairment
Differential additions
Consider uraemic gastritis, renal colic (if structural renal disease), CAPD peritonitis (if on peritoneal dialysis), renal cell carcinoma, and drug accumulation (opioids, NSAIDs, metformin).
Analgesia adjustments
Paracetamol: reduce max dose. NSAIDs: avoid if eGFR < 30. Morphine: active metabolite (M6G) accumulates — extend interval or use fentanyl/hydromorphone. Codeine: avoid (respiratory depression risk). Tramadol: reduce dose by 50% if eGFR < 30.
Hepatic Impairment
Differential additions
Spontaneous bacterial peritonitis (SBP) in ascites, hepatocellular carcinoma, portal hypertensive gastropathy, Budd-Chiari syndrome, hepatic hydrothorax. In chronic liver disease, even mild abdominal pain warrants careful assessment.
Analgesia adjustments
Paracetamol: max 2 g/day in severe hepatic impairment. Avoid NSAIDs (hepatorenal syndrome risk, GI bleed). Codeine/morphine: sedation risk. Avoid diazepam (prolonged half-life). Opioids: use cautiously at reduced doses.
Immunocompromised
Unique considerations
Cytomegalovirus (CMV) colitis, neutropenic enterocolitis (typhlitis), invasive fungal infections, Clostridioides difficile, post-transplant lymphoproliferative disorder, graft-versus-host disease (GI tract). Fever and pain may be blunted by immunosuppression — low threshold for CT imaging.
Neutropenic sepsis
Abdominal pain + neutrophils < 0.5 × 10⁹/L = neutropenic sepsis until proven otherwise. Empirical broad-spectrum antibiotics: piperacillin-tazobactam 4.5 g IV TDS or meropenem 1 g IV TDS. Urgent haematology referral.
Aboriginal and Torres Strait Islander Health Considerations
Aboriginal and Torres Strait Islander Health
Aboriginal and Torres Strait Islander Australians experience significantly higher rates of gastrointestinal disease and worse outcomes from acute abdominal conditions compared to non-Indigenous Australians. Culturally safe, trauma-informed care is essential.
Key message: Do not attribute abdominal pain in Aboriginal and Torres Strait Islander patients to "functional" or "psychogenic" causes without appropriate investigation. Delayed diagnosis of surgical conditions due to implicit bias contributes to poorer outcomes. Investigate with the same urgency as any other patient, adjusting for access barriers.
📚 References
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- 2. Australian Institute of Health and Welfare (AIHW). Aboriginal and Torres Strait Islander Health Performance Framework: Summary report 2023. Canberra: AIHW; 2023.
- 3. Petrov MS, Yadav D. Global epidemiology and holistic prevention of pancreatitis. Nat Rev Gastroenterol Hepatol. 2019;16(4):253–255.
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- 7. Royal Australian College of General Practitioners (RACGP). Guidelines for Preventive Activities in General Practice (Red Book). 9th ed. Melbourne: RACGP; 2018 (updated 2024). (Bowel cancer screening, H. pylori, coeliac disease screening.)
- 8. Australasian Society for Infectious Diseases (ASID). Therapeutic Guidelines: Antibiotic. Version 16. Melbourne: Therapeutic Guidelines Limited; 2022. (Antibiotic recommendations for intra-abdominal infections, UTI, H. pylori.)
- 9. RHDAustralia (ARF/RHD writing group). National Guidelines for Prevention, Diagnosis and Management of Acute Rheumatic Fever and Rheumatic Heart Disease. 3rd ed. Darwin: Menzies School of Health Research; 2020 (updated 2023).
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