What are the differential diagnoses for abdominal pain and their associated signs and symptoms?

Differential Diagnoses for Acute Abdominal Pain by Location

The differential diagnosis for acute abdominal pain is organized by anatomic location, with the most common causes being gastroenteritis, appendicitis, acute cholecystitis, small-bowel obstruction, pancreatitis, renal colic, perforated peptic ulcer, cancer, and diverticulitis 1, 2.

Common Causes Across All Presentations

Approximately one-third of emergency department presentations for abdominal pain remain undiagnosed, one-third are appendicitis, and one-third represent other documented pathology 1. The most frequent diagnoses include:

• Gastroenteritis and nonspecific abdominal pain (most common overall) 2
• Appendicitis (most common surgical cause)
• Acute cholecystitis
• Small-bowel obstruction
• Pancreatitis
• Renal colic/urolithiasis
• Perforated peptic ulcer
• Diverticulitis
• Cancer

Right Upper Quadrant Pain

Acute cholecystitis is the primary diagnostic consideration 3.

Key Signs and Symptoms:

• Right upper quadrant tenderness
• Murphy's sign (inspiratory arrest with palpation)
• Fever (may be present)
• Nausea and vomiting
• Elevated hepatobiliary markers

Associated Conditions:

• Cholelithiasis
• Hepatobiliary disease
• Complicated pancreatic processes
• Pneumonia (extra-abdominal cause)

Right Lower Quadrant Pain

Appendicitis is the primary concern 3, 2.

Classic Signs and Symptoms:

• Pain preceding vomiting (critical distinguishing feature)
• Decreased or absent bowel sounds
• Psoas sign (pain with hip extension)
• Obturator sign (pain with hip internal rotation)
• Rovsing sign (right lower quadrant pain with left lower quadrant palpation)
• Right lower quadrant rebound tenderness
• Guarding and rigidity
• Fever and leukocytosis

Other Considerations:

• Tubo-ovarian abscess (in patients with female reproductive organs)
• Ectopic pregnancy
• Adnexal torsion
• Urolithiasis
• Mesenteric lymphadenitis (especially in children)

Left Lower Quadrant Pain

Diverticulitis is the primary diagnosis 1, 2.

Signs and Symptoms:

• Left lower quadrant tenderness
• Fever
• Leukocytosis
• Altered bowel habits
• Localized peritoneal signs

Important Caveat:

Right-sided diverticulitis occurs more frequently in Asian populations and should not be dismissed 4.

Other Considerations:

• Appendicitis epiploica (recognize to avoid unnecessary surgery) 4
• Sigmoid volvulus
• Pelvic inflammatory disease
• Ovarian pathology

Nonlocalized/Diffuse Abdominal Pain

When pain is diffuse with fever, suspect intra-abdominal abscess, perforation, or bowel obstruction/infarction 1.

Broad Differential:

• Gastrointestinal perforation or inflammation
• Bowel obstruction or infarction
• Abscesses (anywhere in abdomen)
• Nephrolithiasis
• Tumor/malignancy
• Mesenteric ischemia

Special Populations:

Elderly patients:

• Laboratory tests may be nonspecific or normal despite serious infection 1
• May present with atypical or absent clinical signs 5
• Higher threshold needed for imaging

Neutropenic/immunocompromised patients:

• Typical signs of abdominal sepsis may be masked 1
• Diagnosis often delayed
• Associated with high mortality
• Lower threshold for advanced imaging

Red Flag Symptoms Requiring Urgent Surgical Consultation

These symptoms indicate potentially life-threatening conditions 6, 2:

• Severe, localized pain that increases in intensity
• Pain preceding vomiting (not vomiting preceding pain)
• Bilious vomiting
• Hematochezia
• Guarding and rigidity
• Peritoneal signs
• Hemodynamic instability

Extra-Abdominal Causes Not to Miss

• Respiratory infections (especially pneumonia) 2
• Abdominal wall pain (diagnosed by sonopalpation) 4, 5
• Iliopsoas syndrome (often undetected) 4
• Myocardial infarction
• Diabetic ketoacidosis

Gynecologic Causes in Patients with Female Reproductive Organs

Always consider these diagnoses 2:

• Ectopic pregnancy (obtain β-hCG immediately)
• Pelvic inflammatory disease
• Adnexal/ovarian torsion
• Tubo-ovarian abscess
• Ruptured ovarian cyst

Urologic Causes

• Urolithiasis/renal colic 1, 2
• Urinary tract infection
• Pyelonephritis
• Testicular torsion (in males) 6

Critical Pitfalls to Avoid

1. Don't assume normal labs exclude serious pathology, especially in elderly patients 1
2. Re-examine patients with severe acute pain if initial workup is normal 5
3. Don't overlook abdominal wall pain - it's frequently misdiagnosed as intra-abdominal pathology 5
4. Beware of "red herrings" - question whether your initial diagnosis is correct 5
5. Right-sided diverticulitis exists and is more common in Asian populations 4
6. Recognize appendicitis epiploica to prevent unnecessary operations 4