ICD-10 Guide

Acute Appendicitis

ICD-10 Coding for Acute Appendicitis(K35.2, K35.3, K35.8)

PRIMARY SPECIALTYGeneral Surgery

COMPLEXITYHigh

LAST UPDATED09/15/2025

Sam Tuffun, PT, DPT

Physical Therapist | Medical Coding & Billing Contributor

Diagnosis Overview

What is Acute Appendicitis?

Acute appendicitis is an inflammation of the appendix, often resulting from obstruction, infection, or foreign bodies. Key clinical points include: 1) It is a common surgical emergency, particularly in young adults. 2) Symptoms typically include right lower abdominal pain, fever, and nausea. 3) Diagnosis is often confirmed through imaging studies such as ultrasound or CT scans. 4) Early intervention is crucial to prevent complications like perforation. 5) Appendectomy is the standard treatment. Etiologically, acute appendicitis can arise from fecaliths, lymphoid hyperplasia, or tumors. Pathophysiologically, obstruction leads to increased intraluminal pressure, bacterial overgrowth, and inflammation. Clinically, patients present with abdominal pain that migrates from the periumbilical region to the right lower quadrant, often accompanied by rebound tenderness and guarding.

Key Clinical Considerations:

Diagnosis requires clinical evidence of right lower quadrant pain, tenderness, and fever.
Signs include McBurney's point tenderness, rebound tenderness, and guarding.
Resolution criteria involve the absence of symptoms post-appendectomy or conservative management.
Imaging findings may include an enlarged, non-compressible appendix on ultrasound or CT, with possible peri-appendiceal fluid.

Clinical Information

Clinical Criteria & Documentation Requirements

Documentation must include patient history, physical examination findings, and imaging results.
Compliant documentation: 'Patient presents with right lower quadrant pain and fever, imaging confirms appendicitis.' Non-compliant: 'Patient has stomach pain.'
Template phrases: 'Patient diagnosed with acute appendicitis based on imaging findings.'
Medical necessity requires documentation of symptoms, diagnostic tests, and treatment rationale.

Coding Guidelines

Usage Guidelines & Examples

Use K35.2 for acute appendicitis with localized peritonitis, e.g., a patient presenting with right lower quadrant pain and fever.
Do NOT use this code for chronic appendicitis or other gastrointestinal disorders.
Correct usage: K35.2 for a patient with acute symptoms; incorrect: K35.3 for a patient with a history of appendicitis without current symptoms.
Common errors include using the wrong code for chronic conditions; ensure clinical documentation supports the acute diagnosis.

Code Exclusions

Important Exclusions

Excluded conditions include chronic appendicitis (K35.0) and appendiceal abscess (K35.4).
Use K35.0 for chronic cases instead.
Common exclusion errors include misclassifying chronic cases as acute; ensure documentation reflects the acute nature.
Certain conditions are excluded to maintain specificity in coding for acute presentations.

Specialty Focus

Primary Specialty

General Surgery

Specialty Applications

This diagnosis applies to patients presenting with acute abdominal pain suggestive of appendicitis.
Appropriate in emergency settings where surgical intervention is considered.
Inpatient settings typically involve surgical management, while outpatient may involve initial evaluation.
General surgery is the primary specialty involved in the management of acute appendicitis.

Coding Complexity

High Complexity

This diagnosis requires careful attention to:

Comprehensive clinical documentation
Accurate code selection based on clinical criteria
Proper exclusion considerations
Specialty-specific coding guidelines

Documentation

Documentation Templates

Template 1

Template: 'Acute appendicitis diagnosed based on imaging findings of an enlarged appendix.'

Template 2

Template: 'Patient presents with right lower quadrant pain consistent with acute appendicitis.'

Template 3

Template: 'Diagnostic criteria met: imaging shows appendiceal inflammation.'

Template 4

Template: 'Treatment plan includes laparoscopic appendectomy for acute appendicitis.'

Billing Information

Billing Considerations

Ensure proper documentation for billing
Verify code specificity requirements
Check for any additional codes needed
Review payer-specific guidelines

Common Issues

Insufficient clinical documentation
Incorrect code selection
Missing supporting diagnoses
Timing and frequency documentation

Frequently Asked Questions

What documentation is required for this code?

Documentation must include symptoms, imaging results, and treatment rationale.

When should this code be used vs similar codes?

Use K35.2 for acute appendicitis; K36 for unspecified cases.

What are common billing issues with this code?

Issues often arise from lack of supporting documentation; ensure all clinical findings are recorded.

What procedures are commonly associated?

CPT codes for appendectomy (44950) are commonly associated with this diagnosis.

What is Acute Appendicitis?

Key Clinical Considerations:

Diagnosis requires clinical evidence of right lower quadrant pain, tenderness, and fever.
Signs include McBurney's point tenderness, rebound tenderness, and guarding.
Resolution criteria involve the absence of symptoms post-appendectomy or conservative management.
Imaging findings may include an enlarged, non-compressible appendix on ultrasound or CT, with possible peri-appendiceal fluid.

Acute Appendicitis

Diagnosis Overview

Key Clinical Considerations:

Clinical Information

Clinical Criteria & Documentation Requirements

Coding Guidelines

Usage Guidelines & Examples

Code Exclusions

Important Exclusions

Related ICD-10 Codes

Related CPT Codes

Specialty Focus

Primary Specialty

Specialty Applications

Coding Complexity

Documentation

Documentation Templates

Template 1

Template 2

Template 3

Template 4

Billing Information

Billing Considerations

Common Issues

Frequently Asked Questions

What documentation is required for this code?

When should this code be used vs similar codes?

What are common billing issues with this code?

What procedures are commonly associated?

Acute Appendicitis

Diagnosis Overview

Key Clinical Considerations:

Clinical Information

Clinical Criteria & Documentation Requirements

Coding Guidelines

Usage Guidelines & Examples

Code Exclusions

Important Exclusions

Related ICD-10 Codes

Related CPT Codes

Specialty Focus

Primary Specialty

Specialty Applications

Coding Complexity

Documentation

Documentation Templates

Template 1

Template 2

Template 3

Template 4

Billing Information

Billing Considerations

Common Issues

Frequently Asked Questions

What documentation is required for this code?

When should this code be used vs similar codes?

What are common billing issues with this code?

What procedures are commonly associated?