Fever + Abdominal Pain + Vomiting: Clinical Approach

Differential Diagnosis by Frequency

Key Diagnoses to Prioritize

1. Acute Appendicitis (must always rule out first)

• The most common cause of acute abdominal pain requiring surgery in patients under 50, with a lifetime risk of 8.6% (males) and 6.9% (females)
• Classic sequence: anorexia → nausea → periumbilical pain → vomiting → pain migrates to RLQ within 6-8 hours
• Low-grade fever (~38°C) + mild leukocytosis in uncomplicated cases
• Higher fever + higher WBC = suspect perforation or abscess
• Pain preceding vomiting is a key distinguishing feature (vs. gastroenteritis where vomiting may come first)
• Alvarado Score for quick bedside assessment (Sleisenger & Fordtran's, p. 172):

• Score 5-6: suggestive; 7-8: probable; 9-10: very likely - refer to surgery or order imaging
• Imaging: Graded compression ultrasound first; if negative/inconclusive, CT abdomen/pelvis with IV contrast (most sensitive)
• Treatment: Appendectomy or non-operative management (IV antibiotics) for select uncomplicated cases

2. Acute Gastroenteritis

• Diarrhea typically accompanies fever + vomiting; pain is poorly localized and crampy, no peritoneal signs
• If peritoneal signs are present, consider appendicitis instead
• Important: isolated vomiting without diarrhea should NOT be labeled gastroenteritis - the differential is broad
• Bacterial causes include Salmonella (high fever, headache, rose spots), Campylobacter (fever, bloody diarrhea, abdominal pain), Shigella (tenesmus, hematochezia), and others
• Enteric/typhoid Salmonella can present with prolonged high fever, abdominal pain, and constitutional symptoms

3. Acute Cholecystitis / Biliary Colic

• Nausea, vomiting, fever, jaundice + leukocytosis suggests complicated biliary disease
• Pain typically in the RUQ or epigastric region, may radiate to right shoulder
• Murphy's sign positive on examination
• Diagnosis: abdominal ultrasound (first line), MRCP if needed

4. Acute Pancreatitis

• Epigastric pain radiating to the back, fever, vomiting
• May progress from biliary colic
• Elevated serum lipase (>3x upper normal) is diagnostic
• CT abdomen for severity grading if needed

5. Other Important Causes

Diagnostic Approach (Step-by-Step)

History

• Location, onset, and radiation of pain
• Sequence: did pain or vomiting come first?
• Character: colicky (obstruction, renal colic) vs. constant (peritonitis, appendicitis)
• Associated diarrhea, jaundice, urinary symptoms, last menstrual period (women)
• Food history, sick contacts, travel history
• Past surgical history (prior surgeries = risk of adhesions/obstruction)

Physical Examination

• Vital signs: temperature, HR (tachycardia), BP (sepsis?)
• Inspect: distension, guarding, rigidity
• Palpate: localize tenderness - RLQ (appendicitis), RUQ (cholecystitis), epigastric (pancreatitis), LLQ (diverticulitis)
• Special signs:
  • Rebound tenderness (peritoneal irritation)
  • Murphy's sign (cholecystitis)
  • Rovsing's sign / Psoas sign (appendicitis)
  • CVA tenderness (pyelonephritis)

Investigations

• CBC: leukocytosis (infection/inflammation); left shift suggests bacterial cause
• CRP: elevated in inflammation
• LFTs + bilirubin: biliary disease
• Serum lipase/amylase: pancreatitis
• Urinalysis/urine culture: UTI or pyelonephritis
• Urine/serum hCG: ectopic pregnancy in women of reproductive age
• Blood cultures: if sepsis is suspected
• Imaging:
  • Erect CXR: free air under diaphragm (perforated viscus)
  • Abdominal X-ray: obstruction, calcified gallstones/renal stones
  • Ultrasound abdomen: first line for RUQ pathology, appendicitis
  • CT abdomen/pelvis with IV contrast: most sensitive for appendicitis, diverticulitis, pancreatitis complications

Red Flags (Requiring Urgent/Emergent Action)

• Peritoneal signs (rigidity, guarding, rebound) = possible perforation
• Hemodynamic instability (hypotension, tachycardia) = septic shock
• Vomiting bile or feculent material = obstruction
• High fever >39°C with severe leukocytosis = perforation, abscess, sepsis
• Free air on imaging = perforated viscus (emergency surgery)

Management Principles

• Surgical emergencies (perforation, appendicitis, ischemia): IV access, IV fluids, NPO, surgical consult, antibiotics
• Medical causes (gastroenteritis, PID, pyelonephritis): appropriate antibiotics, supportive care, hydration
• Analgesia should NOT be withheld - it does not obscure diagnosis and improves cooperation with examination

Sources: Sleisenger & Fordtran's Gastrointestinal and Liver Disease | Rosen's Emergency Medicine | Tintinalli's Emergency Medicine