The "Use additional code" instruction in ICD-10-CM indicates that a secondary code should be added to provide more complete information about a condition. As part of the official ICD-10 coding guidelines, this instruction appears on the etiology code, directing coders to add codes that capture related manifestations, organisms, or other relevant clinical details.
Understanding Use Additional Code
Unlike the "Code First" instruction which appears on manifestation codes, "Use additional code" appears on primary/etiology codes. It tells the coder that while the current code can be used alone, additional codes provide more complete documentation.
Key Difference from Code First
"Use additional code" is permissive - it indicates additional codes may be added. "Code first" is mandatory - the underlying condition must be sequenced first.
Common Scenarios Requiring Additional Codes
Infectious Agents
Many infection codes include "Use additional code to identify the infectious agent." This allows capture of the specific organism causing the infection.
External Causes
Injury codes often include instructions to use additional external cause codes (Chapter 20) to document how the injury occurred.
Associated Conditions
- Tobacco use, dependence, or history
- Alcohol use or dependence
- Body mass index (BMI)
- Associated manifestations
Examples
Pneumonia with Organism
- Primary: J15.9 (Unspecified bacterial pneumonia)
- Additional: B96.xx (Specific bacterial agent)
COPD with Tobacco Use
- Primary: J44.1 (COPD with acute exacerbation)
- Additional: F17.210 (Nicotine dependence, cigarettes)
Validate Against ICD 10 CM Coding Guidelines
Our Code Auditor identifies when additional codes are needed based on official FY2026 guidelines.
Look up ICD 10 CM codes to find diagnosis codes before validation.
Best Practices
- Review all "Use additional code" notes when assigning codes
- Check medical documentation for the information required by additional codes
- Don't add additional codes without supporting documentation
- Query providers when needed information is missing
Missing additional codes, particularly for HCC-relevant conditions, can impact risk adjustment accuracy. Learn more about coding completeness in our RADV audit risk guide.