Denial Code: 04

Denial Code 05

Definition:

The procedure code is inconsistent with the modifier used, or a required modifier is missing.

What is denial code 04?

Denial code CO-04 indicates that the procedure code billed is either incompatible with the modifier submitted or a modifier is required but missing altogether. Modifiers are essential for conveying additional information about a service or procedure, such as whether it was bilateral, reduced, discontinued, or performed by multiple providers. Incorrect or absent modifiers lead to claim denials due to coding inconsistencies.

Practical Examples

Example 1#

Scenario:
A physician submits claim with CPT code 99213 (office visit for establish patient) with modifier "50" to Medicare.
After processing, Medicare denied CPT with CO 04 and give remark code: N519
Remark Code N519: "Invalid combination of HCPCS code and modifier(s)."

Let's break down the issue:
Office visits (E/M codes like 99213) cover the physician's work for the whole patient, not specific body parts that come in pairs.
The 50 modifier is used for procedures done on both sides of the body (like operating on both knees). You can't have a "bilateral office visit."
CO 04 means there's a modifier issue.
RARC N519 specifically tells you the code and modifier are an "invalid combination."

Resolution:
Simply remove the 50 modifier attached with the office visit code. (E/M services don't need it). Rebill the claim with just 99213.

Example 2#

Scenario:
An orthopedic surgeon performed a surgical arthroscopic meniscectomy on only one meniscus on the left knee and submit just 29881 CPT to BCBS.
Later on, we received ERA, where insurance denied CPT with CO 04 and M123 remark code.
Remark Code M123: "Missing/incomplete/invalid modifier(s)."

Let's break down the issue:
Laterality is Crucial: CPT 29881 describes a procedure on one knee (medial OR lateral meniscectomy). However, a patient has two knees (left and right). Without a modifier, the insurance company doesn't know which knee the procedure was performed on.
CO 04 means there's modifier issue.
RARC M123 tells us that required modifier is missing or invalid.

Resolution:
Simply attach LT modifier (it tells BCBS, the procedure was performed on the left knee) with CPT 29881 and resubmit the claim to BCBS.

Example 3#

Scenario:
An ophthalmologist perform fundus photography on right eye. Submit 92250 with ICD "H35.30 – Unspecified macular degeneration" to insurance company.
We received ERA denied with CO 04 and remark code MA130
MA130 – "Your claim contains incomplete and/or invalid information, and no appeal rights are afforded because the claim is un-processable."

Let's break down the issue:
For diagnostic tests like 92250, Medicare and many commercial payers require a laterality modifier (-RT, -LT, or sometimes -50) when the service can be done on one or both eyes.
Since no modifier was used, the payer could not determine which eye the service was performed on — resulting in denial under CO-04.
RARC MA130 tells us that claim need to be corrected and resubmit for proper processing.

Resolution:
Simply attach RT modifier (it tell insurance company, the procedure was performed on right eye) with 92250 and resubmit the claim to insurance company.

Why Does Denial code 04 Occur?

1. Inappropriate modifier attached to the procedure code (e.g., using modifier 50 with E/M).
2. Missing required modifier (e.g., 59, 25, 51 when needed to distinguish procedures).
3. Improper combination of procedure and modifier (based on payer’s coding edits or NCCI guidelines).
4. Failure to follow payer-specific modifier rules, especially for bilateral, anatomical, or surgical services.

How to avoid / ways to mitigate Denial code 04?

1. Check Coding Accuracy: Ensure the procedure code and bill type match the place where the service was provided.
2. To reduce CO-04 denials, ensure procedure codes are accurately paired with appropriate modifiers. Use official coding tools like CPT and HCPCS manuals, and refer to Medicare’s NCCI edits for guidance. Understand the purpose and context of common modifiers—such as -25 (separate E/M), -59 (distinct service), and -50 (bilateral)—to apply them correctly.
3. Stay current with payer-specific policies, as insurers like BCBS, UHC, and Aetna often have unique modifier requirements. Use their provider manuals and bulletins to guide compliant coding. Implement pre-bill audits or use scrubber tools to flag modifier errors before claims are submitted.
4. Regular education and training for coding staff is essential. Focus on modifier updates, common denial trends, and payer-specific rules. Maintain strong communication between coders, billers, and providers to ensure clean, compliant claim submissions.

Denial Code 05