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CO-182 Denial Code: Modifier Invalid on DOS

CO-182 means a modifier on the service line was not valid on the date of service. The modifier may have been discontinued, not yet effective, or not recognized by the payer on that date. Replace it with a valid modifier and submit a corrected claim.

Quick facts

Code
CO-182 (CARC 182)
Status
Active In use since June 30, 2005; last modified September 30, 2007.
Code set
Claim Adjustment Reason Codes (CARC)
Group codes
  • CO (Contractual Obligation): The provider is responsible for the coding error. The amount is not billable to the patient.
Official description
Procedure modifier was invalid on the date of service.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What CO-182 means

CARC 182 reads “Procedure modifier was invalid on the date of service.” Modifiers in box 24D refine the meaning of a procedure code. Like the codes themselves, modifiers have effective dates. If a modifier was discontinued before the date of service, wasn’t yet effective, or isn’t in the payer’s valid list for that date, the line is denied.

It’s a technical coding error, and usually fixed quickly with a corrected claim.

Example: a practice keeps using a program-specific modifier after the program ended and the modifier was discontinued. Claims after the end date are denied CO-182. The practice removes the modifier (or replaces it with the current equivalent) and resubmits.

Common causes

  • Discontinued modifiers still in templates or fee schedules.
  • New modifiers billed before the payer adopts them.
  • Typos, such as letter-number swaps that produce a modifier that doesn’t exist.
  • Payer-specific modifiers used with a payer that doesn’t recognize them.
  • Retro-billing old claims with modifier rules that applied later, or vice versa.
  • Lowercase or extra characters introduced by manual entry or a clearinghouse mapping, so a valid modifier arrives in a form the payer can’t read.

When several lines on the same claim carry the same modifier, expect the same denial on each. Fixing the template once usually clears the whole group of claims.

How to fix it

  1. Identify the invalid modifier from the ERA line and remark codes.
  2. Check its effective and end dates and the payer’s modifier policy.
  3. Replace or remove it, using the modifier valid for the date of service and the situation.
  4. Submit a corrected claim (resubmission code 7 in box 22), or a new claim if the payer rejected it before adjudication.
  5. If the modifier was valid, contact the payer to request reprocessing.

How to prevent it

  • Review modifier lists during annual and quarterly code updates.
  • Clean up templates and default modifiers in your EHR and billing system.
  • Maintain payer-specific modifier rules for your major payers.
  • Scrub modifiers against the date of service before sending claims. The Claims Validator checks modifier validity as part of pre-submission review. For modifier-related bundling issues, see NCCI and modifier denials.

Remark codes that may appear with CO-182

  • N823 (Incomplete/Invalid procedure modifier(s).): The procedure modifier is incomplete or invalid.
  • N519 (Invalid combination of HCPCS modifiers.): The combination of HCPCS modifiers on the line is invalid.
  • N822 (Missing procedure modifier(s).): A required modifier is missing, which may accompany an invalid one.
  • CO-181 (Procedure code was invalid on the date of service.): The procedure code itself was invalid on the date of service.
  • CO-4 (The procedure code is inconsistent with the modifier used.): The procedure code is inconsistent with the modifier used, rather than the modifier being invalid for the date.
  • CO-199 (Revenue code and Procedure code do not match.): The revenue code and procedure code don't match, another code-set issue.

CO-182 FAQ

Do modifiers really change by date?

Yes. HCPCS Level II modifiers are added and discontinued over time, and payers adopt new modifiers on specific dates. Medicare, for example, has introduced and retired modifiers tied to specific programs.

What is the difference between CO-182 and CO-4?

CO-4 says the procedure code is inconsistent with the modifier used. CO-182 says the modifier itself wasn't valid on the date of service.

How do I find valid modifiers?

Check the current CPT and HCPCS Level II modifier lists, and the payer's own modifier policies. Payers sometimes accept a modifier later than its national effective date.

Is it safe to just remove the invalid modifier?

Only if no modifier is needed for the service. If a modifier is required to describe the situation, replace the invalid one with the currently valid equivalent, or the line may be denied for a missing modifier instead.