How do I resolve a CO-4 denial?

Identify the specific modifier that caused the inconsistency — the payer's remittance or an edit report should indicate the problematic modifier. Review the CPT code's modifier indicator in the Medicare Physician Fee Schedule to confirm which modifiers are appropriate. If the modifier was applied in error: remove it and resubmit the corrected claim. If the modifier is clinically appropriate but the payer's editing software is incorrect: appeal with documentation of the specific service rendered and why the modifier is justified. Consult the AMA CPT codebook modifier guidance for the specific CPT code in question.

Can I appeal a CO-4 denial?

Yes. CO-4 denials are typically appealable with a 72% success rate. Resolution difficulty is Medium and typically takes 7-14 days.

835 Denial Combination

CO-4

Contractual Obligation · Service-Line Level Adjustment

What This Combination Means

The procedure code is inconsistent with the modifier(s) submitted. A modifier was applied that is clinically inconsistent with the procedure (e.g., a bilateral modifier on a procedure that is inherently bilateral, or a modifier that requires a specific place of service not matching what was billed).

72%

Appeal Success

7-14 days

Avg. Resolution

Medium

Difficulty

Yes

Appealable

Step-by-Step Resolution

Steps tailored specifically to this CO-4 combination — not generic advice.

1
Identify the specific modifier that caused the inconsistency — the payer's remittance or an edit report should indicate the problematic modifier.
2
Review the CPT code's modifier indicator in the Medicare Physician Fee Schedule to confirm which modifiers are appropriate.
3
If the modifier was applied in error: remove it and resubmit the corrected claim.
4
If the modifier is clinically appropriate but the payer's editing software is incorrect: appeal with documentation of the specific service rendered and why the modifier is justified.
5
Consult the AMA CPT codebook modifier guidance for the specific CPT code in question.

Specialty Context

How CO-4 typically presents across different practice types.

Dental

Dental modifiers are limited but include toothsurf codes. Modifier conflicts are less common in dental but appear in dental-medical crossover claims.

Medical

Common modifier conflicts include: Modifier 50 (bilateral) on procedures with a bilateral indicator of 0 or 2, Modifier 62 (two surgeons) without a co-surgeon agreeing, or professional and technical component modifiers applied incorrectly.

Behavioral Health

Telehealth modifiers (95, GT) must be paired with eligible services and the correct place of service code (02 or 10). A mismatch between the modifier and POS triggers CO-4.

Individual Code References

View the standalone definition for each code in this combination.

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