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v1.0.0
ICD-10 Guide
DiagnosesAllergy Unspecified

Allergy Unspecified

ICD-10 Coding for Unspecified Allergy(T78.40XA)

PRIMARY SPECIALTYEmergency Medicine
COMPLEXITYHigh
LAST UPDATED09/15/2025
Sam Tuffun, PT, DPT
Physical Therapist | Medical Coding & Billing Contributor

Diagnosis Overview

What is Allergy Unspecified?
Essential facts and insights about Unspecified Allergy

Key Clinical Considerations:

  • Common symptoms include itching, hives, swelling, and respiratory distress.
  • Diagnostic tests may include skin prick tests, serum IgE tests, and patient history evaluation.
  • Physical exam may reveal urticaria, angioedema, or signs of anaphylaxis.

Clinical Information

Clinical Criteria & Documentation Requirements

  • Document patient history of allergies, symptoms, and any previous reactions.
  • Use specific terminology such as 'allergic reaction' or 'hypersensitivity'.
  • Examples include noting the onset, duration, and severity of symptoms.

Coding Guidelines

Usage Guidelines & Examples

  • Follow usage guidelines to differentiate between unspecified and specific allergies.
  • Common errors include misclassifying the type of allergy or failing to document symptoms adequately.

Code Exclusions

Important Exclusions

  • Excluded conditions include specific allergies like food allergies or drug allergies.
  • Alternative codes may include T78.41 for allergic reaction to food or T78.42 for allergic reaction to drugs.

Related ICD-10 Codes

Primary Codes
T78.40
Allergy, unspecified
Ancillary Codes
R21
Differential Codes
J30.9

Related CPT Codes

CPT codes will be available in a future update.

Specialty Focus

Primary Specialty

Emergency Medicine

Specialty Applications

  • Patient populations include individuals with known or suspected allergies.
  • Clinical settings include emergency departments and urgent care facilities.

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

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 are the documentation requirements?

Document the patient's allergy history, symptoms, and any treatments administered.

What are the billing considerations?

Ensure accurate coding to reflect the severity and type of allergic reaction for appropriate reimbursement.