USMLE Prep - Medical Reference Library

Acute Appendicitis — Diagnosis and Initial Management

System: General Surgery • Reviewed: Aug 31, 2025 • Step 1Step 2Step 3

Synopsis:

Classic migration of pain to right lower quadrant with anorexia and fever; use ultrasound or CT to confirm; give antibiotics and timely surgical consult.

Key Points

  • Stabilize ABCs; begin targeted evaluation without delaying life-saving therapy.
  • Use system-specific risk tools to guide testing and disposition.
  • Order high-yield tests first; escalate imaging when indicated.
  • Start evidence-based initial therapy and reassess frequently.

Algorithm

  1. Primary survey and vitals; IV access and monitors.
  2. Focused history/physical; identify red flags and likely etiologies.
  3. Order system-appropriate labs and imaging (see Investigations).
  4. Initiate guideline-based empiric therapy (see Pharmacology).
  5. Reassess response; arrange consultation and definitive management.

Clinical Synopsis & Reasoning

Appendicitis typically presents with periumbilical pain migrating to the RLQ, anorexia, and fever, with leukocytosis; ultrasound or CT confirms diagnosis. Consider mimics (gastroenteritis, ovarian torsion, mesenteric adenitis) and perforation risk when symptoms are prolonged or systemic toxicity is present. Risk scores (Alvarado, AIR) support decision‑making and imaging selection, particularly in pregnancy and pediatrics.


Treatment Strategy & Disposition

Uncomplicated disease is treated with early appendectomy or, in selected cases, antibiotics with shared decision‑making about recurrence risk. Perforation with abscess may warrant antibiotics and interval appendectomy after drainage. Provide peri‑operative antibiotics, analgesia, and VTE prophylaxis per risk. Most patients go to surgical service; admit when complicated or with comorbidities requiring monitoring.


Epidemiology / Risk Factors

  • Risk factors vary by condition and patient profile

Investigations

TestRole / RationaleTypical FindingsNotes
CBCBaseline hematologyAbnormal counts
BMPElectrolytes/renalDerangements

Typical Antibiotics (Adult examples)

RegimenNotes
Ceftriaxone plus metronidazoleCommon ED combination
Piperacillin tazobactamSevere or perforation concern

Pharmacology

MedicationMechanismOnsetRole in TherapyLimitations
Ceftriaxone + metronidazoleCephalosporin + nitroimidazoleHoursPeri-op/complicated casesAllergy; disulfiram-like (metro)

Prognosis / Complications

  • Prognosis depends on severity, comorbidities, and timeliness of care

Patient Education / Counseling

  • Explain red flags and when to seek emergent care.
  • Reinforce medication adherence and follow-up plan.

Notes

Consider gynecologic and urinary mimics. Perforation or abscess may require percutaneous drainage.


References

  1. WSES Guidelines for Appendicitis — Link
  2. ACS Acute Care Surgery Resources — Link