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N823 Remark Code: Incomplete or Invalid Modifier

N823 means a procedure modifier on the claim line was incomplete or invalid. The modifier may not exist, may not be valid for that code or date, may be in the wrong position, or may conflict with the service billed.

Quick facts

Code
N823 (RARC N823)
Status
Active In use since July 1, 2019; last modified November 1, 2019.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The line was denied for a coding error. The provider corrects it; the patient isn't billed.
Official description
Incomplete/Invalid procedure modifier(s).
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What N823 means

Where N822 says a modifier is missing, N823 says one is present but doesn’t pass the payer’s checks. The two-character code may be malformed or discontinued, may not be allowed with the procedure code, may contradict another modifier on the line, or may not make sense for the provider, place of service, or date.

The app guidance for this code is straightforward: correct the modifiers and refile. It is commonly paired with CARC 4 (procedure inconsistent with modifier) or CARC 182 (modifier invalid on the date of service).

Common causes

  • Typos, such as a letter O entered for a zero.
  • Conflicting pairs, like RT and LT on one line when the payer wants 50 or two lines, or 26 and TC together.
  • Modifier not allowed with the code, such as a component modifier on a code that has no professional/technical split.
  • Discontinued or not yet effective for the date of service.
  • Payer-specific rules, including modifiers one payer accepts and another rejects.

How to fix it

  1. Identify which modifier failed. If there are several, check each against the code and the payer’s policy.
  2. Verify against the documentation that the corrected modifier describes the service actually performed.
  3. Fix the modifier and order in box 24D, splitting lines if the payer requires it for bilateral or multiple services.
  4. Submit a corrected claim with resubmission code 7 in box 22.

How to prevent it

  • Keep modifier tables updated each year in your billing software.
  • Use scrubber edits for invalid code/modifier combinations and conflicting pairs.
  • Review NCCI bundling and modifier rules before appending distinct-service modifiers.

Codes that may appear with N823

  • CO-4 (The procedure code is inconsistent with the modifier used.): The procedure code is inconsistent with the modifier used.
  • CO-182 (Procedure modifier was invalid on the date of service.): The modifier was invalid on the date of service.
  • CO-16 (Claim/service lacks information or has submission/billing error(s).): The claim has a billing error that N823 points to.
  • N822 (Missing procedure modifier(s).): A required modifier was missing entirely.
  • N519 (Invalid combination of HCPCS modifiers.): The combination of two or more modifiers is invalid.
  • CO-236 (This procedure or procedure/modifier combination is not compatible with another procedure or procedure/modifier combination provided on the same day…): A procedure/modifier combination is incompatible with another service on the same day.

N823 FAQ

What makes a modifier invalid?

Common reasons are a typo or discontinued modifier, a modifier that can't be used with that procedure code, one that conflicts with another modifier on the line, or one that doesn't match the provider type or place of service.

Does modifier order matter?

It can. Many payers expect pricing modifiers first and informational modifiers after. Check the payer's guidance if you report more than one.

Can I resubmit without the modifier?

Only if the modifier truly didn't apply. If the service requires one, removing it will usually cause a missing-modifier denial instead.