Top 10 ICD-10 Coding Errors and How to Fix Them
Claim denials cost healthcare organizations billions annually. Many denials stem from preventable ICD-10-CM coding errors. Here are the 10 most common mistakes and how to avoid them.
In This Article
Coding Excludes1 Conflicts
Reporting two codes that have an Excludes1 relationship is one of the most common reasons for claim denials. Excludes1 means the conditions are mutually exclusive and cannot be coded together.
Example: Reporting E11.9 (Type 2 diabetes) with E10.9 (Type 1 diabetes). A patient cannot have both types simultaneously.
✅ Fix: Always validate code combinations against Excludes1 rules before submitting. Use the ICD10Check Excludes Checker to catch these conflicts automatically.
Using Non-Billable Category Codes
Submitting a category header code (like E11) instead of a specific billable code (like E11.9) is a guaranteed denial.
Example: Reporting E11 instead of E11.65 (Type 2 diabetes with hyperglycemia).
✅ Fix: Always code to the highest level of specificity. Check the Browse Codes tree to see available child codes.
Ignoring Inherited Excludes Rules
Many coders check only the specific code for Excludes notes but miss rules inherited from parent categories. Excludes notes at the category level apply to ALL codes within that category.
Example: Code E11.9 itself may not show an Excludes1 for E10 codes, but its parent E11 does. The rule is inherited.
✅ Fix: Always check parent category notes. The ICD10Check Excludes Checker automatically checks inherited rules from all ancestor categories.
Missing Laterality Codes
ICD-10-CM requires laterality (left, right, bilateral, unspecified) for many conditions affecting paired organs. Using an unspecified laterality code when the side is documented can trigger denials.
✅ Fix: Review the medical record for laterality documentation. When the provider documents “right” or “left,” select the corresponding laterality-specific code.
Incorrect 7th Character Extension
Many injury and fracture codes require a 7th character to indicate the episode of care. Using the wrong extension or omitting it entirely results in an invalid code.
✅ Fix: Always check if a code requires a 7th character. Use “A” for initial encounter, “D” for subsequent, and “S” for sequela.
Not Following “Code First” Instructions
Some ICD-10-CM codes include “Code first” or “Use additional code” instructions that specify sequencing requirements. Ignoring these instructions can result in improper code sequencing.
✅ Fix: Read all instructional notes under a code. The code detail pages on ICD10Check show these instructions clearly.
Upcoding and Overcoding
Selecting a code with higher specificity or severity than what is documented is considered upcoding. This can lead to audits, penalties, and fraud allegations.
✅ Fix: Code only what is documented. Query the provider if documentation seems incomplete rather than assuming a higher-specificity code.
Using Outdated Code Sets
ICD-10-CM is updated every October 1. Using codes from the previous fiscal year after the update date will result in invalid code submissions and denials.
✅ Fix: Update your coding references every October 1. ICD10Check uses the current FY2026 dataset (effective October 1, 2025).
Confusing Excludes2 with Excludes1
Some coders drop a code unnecessarily when they see an Excludes2 note, thinking it works the same as Excludes1. This leads to undercoding and potentially lower reimbursement.
✅ Fix: Remember: Excludes1 = never together, Excludes2 = can be together if documented. Read our complete guide to Excludes1 vs Excludes2.
Not Validating Before Submission
The most preventable error of all: submitting claims without running any validation. Many coding conflicts can be caught with a simple pre-submission check.
🧪 Validate Your Codes for Free
Enter your ICD-10 codes into the ICD10Check Excludes Checker and instantly see conflicts.
Open Excludes Checker →Key Takeaways
Most ICD-10 coding errors are preventable with proper tools and attention to detail. Always code to the highest specificity, check Excludes notes including inherited ones, follow sequencing instructions, and validate code combinations before submitting claims.
Bookmark ICD10Check.com for free, instant code lookups and Excludes conflict detection using the official CMS ICD-10-CM 2026 dataset.