Abdominal pain differential diagnosis by location

The differential diagnosis of abdominal pain is unusually wide and unusually dangerous. In one large emergency-department series, 20 conditions accounted for up to 70% of presentations — but more than 150 separate diagnoses were made (Yew et al., American Family Physician 2023). The practical approach is therefore not to name the diagnosis at first contact, but to work in a fixed order: exclude the time-critical catastrophes, then use pain location and base rates to rank what remains, then image or observe according to that ranking.

This is a working reference for clinicians. It covers the structure of the differential, the red flags that override everything else, causes by region, what the commonest diagnoses actually are, which examination signs and laboratory tests earn their place, how imaging choice follows pain location, and why older adults break most of the rules above. Acute abdominal pain is defined in the current AAFP review as non-traumatic abdominal pain lasting fewer than seven days, and accounts for up to 10% of emergency-department visits.

Key takeaways

• Acute abdominal pain is non-traumatic pain of fewer than seven days' duration and causes up to 10% of ED visits; 20 conditions explain up to 70% of cases, yet more than 150 diagnoses were recorded in one large series (AAFP 2023).
• The three findings that reorder your whole plan are haemodynamic instability, peritonitis, and pain out of proportion to the examination.
• The commonest ED diagnoses are mundane: acute gastroenteritis 10.8%, non-specific abdominal pain 10.4%, cholelithiasis 4.5%, urolithiasis 4.3%, diverticulitis 3.8% and appendicitis 3.8% (AAFP 2023).
• Roughly 10% of patients have a urinary cause, and 10% of those aged 65 and over have a respiratory cause — the abdomen is not always the organ at fault (AAFP 2023).
• Analgesia does not impair examination accuracy and is recommended (SORT level A evidence) — withholding it to "preserve the signs" is not supported (AAFP 2023).
• Imaging follows location: ultrasonography for right upper quadrant and pelvic pain, CT with contrast for lower-quadrant, left-upper and generalised pain (AAFP 2015).
• A final diagnosis is usually not made at the first outpatient visit — excluding serious disease is the deliverable (AAFP 2008).

What is the differential diagnosis of abdominal pain?

The differential diagnosis of abdominal pain is the ranked list of conditions that could explain the presentation, generated from the pain's location, onset and character and then narrowed by examination, laboratory tests and imaging. Because the abdomen houses several organ systems and refers pain from outside itself, the list is best built by system rather than by memory.

A workable system-by-system frame, which you then intersect with pain location:

• Gastrointestinal — appendicitis, diverticulitis, bowel obstruction, perforated peptic ulcer, gastroenteritis, inflammatory bowel disease, hernia, mesenteric ischaemia.
• Hepatobiliary and pancreatic — cholelithiasis, cholecystitis, cholangitis, hepatitis, pancreatitis.
• Urological — urolithiasis, pyelonephritis, cystitis, urinary retention.
• Gynaecological and obstetric — ectopic pregnancy, ovarian torsion, ruptured ovarian cyst, pelvic inflammatory disease.
• Vascular — ruptured abdominal aortic aneurysm, aortic dissection, mesenteric ischaemia.
• Extra-abdominal and referred — lower-lobe pneumonia, myocardial infarction, pericarditis, pulmonary embolism.
• Abdominal wall — muscle strain, hernia, herpes zoster, nerve entrapment. The 2008 AAFP review notes these are often misdiagnosed, because clinicians look past the wall to the viscera.
• Metabolic and systemic — diabetic ketoacidosis, adrenal crisis, sickle cell crisis, porphyria, hypercalcaemia, heavy-metal poisoning.

For the reasoning method behind building and pruning a list like this — hypothesis generation, pertinent negatives, and the cognitive errors that derail it — see our pillar guide, what is a differential diagnosis?

What are the red flags in abdominal pain?

The AAFP's 2023 review frames the first task as rapidly identifying patients with haemodynamic instability, peritonitis, or pain out of proportion to the examination findings. Abnormal vital signs — fever, tachycardia, hypotension — identify the highest-risk patients. These features move the patient out of the diagnostic pathway and into a resuscitation and surgical-referral pathway.

Two red flags deserve separate emphasis because they are quiet. Acute mesenteric ischaemia presents with pain disproportionate to the examination; roughly 50% of cases are embolic, and the AAFP review advises CT angiography even in the presence of renal insufficiency, on the grounds that delayed diagnosis is more harmful than contrast exposure. Ruptured abdominal aortic aneurysm carries a risk of death as high as 81% (USPSTF 2019), and population studies in men over 60 found an AAA prevalence of 1.2% to 3.3% — a background rate high enough that the diagnosis belongs on the list for any older patient with abdominal, flank or back pain and shock.

Finally, a pregnancy test is indicated in all premenopausal women with acute abdominal pain, including those using contraception (AAFP 2023). Ectopic pregnancy is the diagnosis that punishes assumption.

What causes abdominal pain in each quadrant?

Pain location narrows the list but never closes it. The AAFP's regional differential groups causes by the organ systems that project pain to each area, and reserves a final "any location" category for the diagnoses that refuse to localise.

• Right upper quadrant — biliary (gallbladder and bile duct disease), hepatic, colonic, renal and pulmonary causes.
• Epigastric — biliary, gastric, pancreatic, cardiac and vascular causes.
• Left upper quadrant — gastric, pancreatic, renal, cardiac and vascular causes.
• Periumbilical — early appendicitis, gastric and small-bowel causes, and vascular causes (including aortic aneurysm).
• Right lower quadrant — colonic (appendicitis, diverticulitis), gynaecological and renal causes.
• Left lower quadrant — colonic (diverticulitis), gynaecological and renal causes.
• Suprapubic — colonic, gynaecological and renal causes, including cystitis.
• Any location — abdominal wall causes, bowel obstruction, mesenteric ischaemia, peritonitis, inflammatory bowel disease, opioid withdrawal, sickle cell crisis, porphyria and heavy-metal poisoning.

Source: Cartwright and Knudson, American Family Physician 2008. Note that the same group's 2023 successor review emphasises how often the answer sits outside the abdomen: about 10% of patients had a urinary aetiology, and 10% of patients aged 65 and over had a respiratory cause.

Which abdominal pain diagnoses are actually most common?

Base rates matter, because a differential ranked by severity alone over-investigates everybody. In the large ED series summarised by the AAFP in 2023, the leading diagnoses were acute gastroenteritis (10.8%), non-specific abdominal pain (10.4%), cholelithiasis (4.5%), urolithiasis (4.3%), diverticulitis (3.8%) and appendicitis (3.8%).

Two of those deserve their own numbers. The lifetime risk of appendicitis is 8.6% in males and 6.7% in females, and appendicitis is the most common non-obstetric surgical emergency in pregnancy at 6.3 per 10,000 antepartum pregnancies (Snyder et al., AAFP 2018). For diverticular disease, diverticulosis affects 5% to 15% of people over 45 and 80% of those over 85; about 25% of people with diverticulosis will develop acute diverticulitis in their lifetime, and up to 15% of acute diverticulitis episodes are complicated (DuBose and Seehusen, AAFP 2021).

Note that "non-specific abdominal pain" is the second commonest outcome, not a failure. The 2008 review states plainly that a final diagnosis is usually not made at the first outpatient visit — which makes safety-netting, documented return advice and planned review part of the diagnosis, not an afterthought.

Which examination signs and tests actually help?

Fewer than clinical teaching implies. The AAFP 2023 review's summary of the classic signs is sobering: no single finding excludes acute cholecystitis, including the Murphy sign and right-upper-quadrant tenderness. The Rovsing, psoas and obturator signs have low sensitivity for appendicitis but modestly increase its likelihood when present. The Carnett sign suggests abdominal wall pain but cannot exclude intra-abdominal pathology. For left-lower-quadrant diverticulitis, clinical suspicion alone has a positive predictive value of up to 65%.

Laboratory tests are similarly limited, and knowing their limits is the clinical skill:

• White cell count and CRP — neither is diagnostic for appendicitis.
• Lipase — a value greater than three times the upper limit of normal suggests pancreatitis in the right clinical context, but pancreatitis can occur with a normal lipase.
• Urinalysis — the absence of haematuria does not exclude urolithiasis; about 16% of confirmed cases had no microscopic haematuria.
• Serum lactate — check it in suspected sepsis or mesenteric ischaemia, accepting that it can be normal early in sepsis.
• Pregnancy test — in every premenopausal woman, regardless of contraception.

Where structured scoring helps, it helps a lot. The Alvarado score is the best-studied clinical decision rule for appendicitis: in adults with a 33% pretest probability, a score of 7 or more carries a positive likelihood ratio of 3.4 (about 87% probability of appendicitis), while a score below 4 has a likelihood ratio of 0.03 and a post-test probability of roughly 3.7% (AAFP 2018). The AAFP 2023 review also reports a CHOKAI score of 6 or more for urolithiasis with LR+ 9.3 and LR− 0.08, and ultrasonography-based cholecystitis scores with LR+ values rising from 1.5 to 10 as the score increases.

How do you choose imaging for abdominal pain?

Imaging choice follows pain location. Ultrasonography is the initial study for right-upper-quadrant pain and for suprapubic or pelvic pain in patients with female reproductive organs; CT with intravenous contrast is the initial study for right-lower, left-lower, left-upper and generalised pain (AAFP 2015, AAFP 2023).

• Appendicitis (non-pregnant) — CT is the most accurate standalone test, with 91% sensitivity and 90% specificity, against 78% and 83% for ultrasonography (AAFP 2015). Ultrasonography-first with selective CT, or a clinical risk score, are legitimate alternatives used widely outside the United States.
• Appendicitis in pregnancy — ultrasonography first (sensitivity 78%, specificity 75%), then MRI if inconclusive (sensitivity 92%, specificity 98%); CT only if MRI is unavailable (AAFP 2023).
• Cholecystitis — ultrasonography has 81% sensitivity and 83% specificity; cholescintigraphy performs better at 96% and 90% (AAFP 2015).
• Diverticulitis — CT has 94% sensitivity and 99% specificity (AAFP 2021). A clinical diagnosis is reasonable in immunocompetent patients without risk factors for complications; image when uncertain or high-risk (AAFP 2023).
• Urolithiasis (flank pain) — no imaging is needed in patients under 35 with typical symptoms, haematuria, response to analgesia and previous stones (AAFP 2023).
• Radiation context — abdominal CT delivers an effective dose of about 10 mSv, against an annual US background dose of 3 mSv; low-dose appendicitis protocols used about 22% of the standard dose with no significant difference in negative-appendicectomy rate (AAFP 2015).

Why is abdominal pain harder to diagnose in older adults?

Because the signs are blunted while the stakes are higher. Patients over 65 with peritonitis are about half as likely to show rebound tenderness or guarding (AAFP 2023). The 2006 AAFP review on older patients is blunter still: the physical examination can be misleadingly benign, and fever, leukocytosis, localised tenderness, rebound, guarding and tachycardia may all be absent.

• More than half of older ED patients with acute abdominal pain require admission; 20% to 33% require immediate surgery, roughly twice the rate in younger patients.
• Overall mortality in retrospective series runs 2% to 13%, and mortality for emergency abdominal surgery 15% to 34%, largely driven by coexisting disease.
• For appendicitis in older patients, the initial diagnosis is correct only about half the time, with higher perforation and mortality rates.
• Cholecystitis frequently lacks its classic features: in one series, over 40% had no nausea and 13% had no abnormal liver tests, fever or leukocytosis.
• Abdominal aortic aneurysm is often misdiagnosed, because it can mimic cholecystitis, perforated ulcer, diverticulitis or renal colic.

Sources: Lyon and Clark, AAFP 2006 and AAFP 2023. The AAFP 2023 review adds that older patients are more likely to have diverticulitis, cholelithiasis, mesenteric ischaemia or urinary retention, and that in one retrospective analysis imaging changed management more than 65% of the time — a strong argument for a lower imaging threshold in this group.

One further equity finding belongs here rather than in a footnote. In one ED study cited by the AAFP, Black and Hispanic patients were 26% and 56% less likely to be classified as high acuity, and about half as likely to receive CT. Diagnostic pathways are not applied evenly, and that is a safety problem as much as a fairness one — the WHO estimates that diagnostic errors occur in 5% to 20% of physician–patient encounters, and that as many as 4 in 10 patients are harmed in primary and ambulatory care (WHO patient safety fact sheet, 2023).

A worked example (illustrative)

Illustrative case, not a real patient. A 72-year-old man presents with four hours of central abdominal pain, now 8/10, with one episode of vomiting. Pulse 104, blood pressure 108/62, temperature 36.9°C. The abdomen is soft with mild periumbilical tenderness and no guarding. He has atrial fibrillation and takes a direct oral anticoagulant.

The reasoning runs in order. First, the overrides: pain out of proportion to a soft abdomen, in an older patient with a cardioembolic source, puts acute mesenteric ischaemia at the top regardless of how well he looks — and CT angiography is indicated even if renal function is impaired. Second, location: periumbilical pain also covers early appendicitis, small-bowel pathology and aortic aneurysm, so the aorta is assessed on the same scan. Third, base rates: gastroenteritis and non-specific pain are commoner than everything above, but they are diagnoses of exclusion here, not starting points. Fourth, the blunted-signs rule: the absent guarding and near-normal temperature carry little reassurance at 72. Lactate is checked and accepted as potentially normal early. Analgesia is given without waiting, because it does not degrade the examination.

Where decision support fits

Abdominal pain is a good test of decision support because the failure mode is omission, not ignorance: 150-plus possible diagnoses, a handful of time-critical ones, and a consultation that is usually running late. Shifaa AI — an AI clinical assistant currently in private beta — is built for that gap. Its differential-diagnosis support surfaces a ranked differential, raises the red-flag presentations ahead of the likely ones, and shows the guidance behind each suggestion so you can check it. It is decision support: it does not diagnose, and the clinician reviews, edits and signs, as we argue in can AI diagnose patients? Because so much of this reasoning has to survive into the record, the assessment and plan are where it has to land cleanly — our free SOAP note template is built around exactly that.

For the same approach applied to two other high-stakes presentations, see chest pain differential diagnosis and headache differential diagnosis. For the prescribing side of the same consultation, see drug–drug interactions: a practical guide for prescribers.

Frequently asked questions

What are the red flags for abdominal pain?

Haemodynamic instability, peritonitis, and pain out of proportion to the examination — plus abnormal vital signs (fever, tachycardia, hypotension). Abrupt or severe onset should prompt consideration of aortic dissection, intra-abdominal haemorrhage, organ ischaemia, biliary or ureteral obstruction, hollow-organ perforation and ruptured abdominal aortic aneurysm. Absent bowel sounds is an alarm sign for mesenteric ischaemia or strangulated small-bowel obstruction.

What is the most common cause of acute abdominal pain?

In emergency-department data summarised by the AAFP, acute gastroenteritis is the single commonest diagnosis at 10.8%, closely followed by non-specific abdominal pain at 10.4%. Cholelithiasis (4.5%), urolithiasis (4.3%), diverticulitis (3.8%) and appendicitis (3.8%) follow. Around 10% of patients have a urinary cause, and 10% of those aged 65 and over have a respiratory cause.

Which imaging test should be ordered for abdominal pain?

It depends on location. Ultrasonography is first-line for right-upper-quadrant pain and for suprapubic or pelvic pain in patients with female reproductive organs. CT with intravenous contrast is first-line for right-lower, left-lower, left-upper and generalised pain. In suspected appendicitis in pregnancy, use ultrasonography first and MRI if inconclusive. Flank pain in patients under 35 with typical renal colic may need no imaging.

Should analgesia be withheld until the abdomen has been examined?

No. The AAFP's 2023 review recommends analgesia with SORT level A evidence: it improves patient comfort and does not impair the accuracy of the abdominal examination. Withholding pain relief to preserve physical signs is not supported by the evidence and delays appropriate care.

References

• Yew KS, George MK, Allred HB. Acute Abdominal Pain in Adults: Evaluation and Diagnosis. American Family Physician, 2023;107(6):585-596. aafp.org/pubs/afp/issues/2023/0600/acute-abdominal-pain-adults.html
• Cartwright SL, Knudson MP. Evaluation of Acute Abdominal Pain in Adults. American Family Physician, 2008;77(7):971-978 — cited here for its regional differential-diagnosis table. aafp.org/pubs/afp/issues/2008/0401/p971.html
• Cartwright SL, Knudson MP. Diagnostic Imaging of Acute Abdominal Pain in Adults. American Family Physician, 2015;91(7):452-459. aafp.org/pubs/afp/issues/2015/0401/p452.html
• Snyder MJ, Guthrie M, Cagle S. Acute Appendicitis: Efficient Diagnosis and Management. American Family Physician, 2018;98(1):25-33. aafp.org/pubs/afp/issues/2018/0701/p25.html
• DuBose J, Seehusen D. Diagnosis and Initial Management of Acute Colonic Diverticulitis. American Family Physician, 2021;104(2):195-197. aafp.org/pubs/afp/issues/2021/0800/p195.html
• Lyon C, Clark DC. Diagnosis of Acute Abdominal Pain in Older Patients. American Family Physician, 2006;74(9):1537-1544. aafp.org/pubs/afp/issues/2006/1101/p1537.html
• US Preventive Services Task Force. Abdominal Aortic Aneurysm: Screening — final recommendation statement, 2019. uspreventiveservicestaskforce.org
• World Health Organization. Patient safety — fact sheet, 11 September 2023 (diagnostic error rates, harm in ambulatory care). who.int/news-room/fact-sheets/detail/patient-safety