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N519 Remark Code: Invalid HCPCS Modifier Combination

N519 means the service line carried a combination of HCPCS or CPT modifiers that the payer considers invalid together. The modifiers contradict each other or cannot be used on the same line, so the payer could not process the service as billed.

Quick facts

Code
N519 (RARC N519)
Status
Active In use since July 1, 2009.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): A provider coding error caused the denial. The patient is not responsible while it can be corrected.
Official description
Invalid combination of HCPCS modifiers.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What N519 means

Modifiers add detail to a procedure code: which side of the body, which component, whether a service was distinct or repeated. Some modifiers cannot logically coexist. A service cannot be both only the professional component and only the technical component, and a single line cannot describe only the right side and only the left side.

N519 tells you the payer’s edits found such a conflict on the line. It is a coding correction, not a coverage decision.

Common causes

  • Component conflicts. 26 and TC billed together instead of the global service or two separate lines.
  • Side conflicts. RT and LT together where the payer wants modifier 50 or separate lines, or 50 combined with RT or LT.
  • Finger, toe, or eyelid modifiers that name different sites on one line.
  • Automated modifier logic in a PM system appending a modifier that conflicts with one the coder entered.
  • Payer-specific pairs that the payer’s policy treats as mutually exclusive.

How to fix it

  1. Look at every modifier in box 24D on the denied line and decide which ones actually describe the service.
  2. Check the payer’s rules for bilateral, component, and site-specific billing.
  3. Rebuild the line. Remove the conflicting modifier, split the service into separate lines, or bill the global service, as the documentation supports.
  4. Resubmit as a corrected claim with resubmission code 7 in box 22 and the original claim number.
  5. Check units in box 24G, since splitting or combining lines often changes them.

How to prevent it

Add claim scrubber edits for known conflicting modifier pairs and review automated modifier rules in your billing system. The NCCI and modifier guide explains how modifier logic interacts with other payer edits.

Codes that may appear with N519

  • CO-4 (The procedure code is inconsistent with the modifier used.): The procedure code is inconsistent with the modifier used.
  • CO-16 (Claim/service lacks information or has submission/billing error(s).): The claim had a billing error; the error is the modifier combination.
  • CO-182 (Procedure modifier was invalid on the date of service.): Used when one of the modifiers was invalid on the date of service.
  • 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 or procedure-modifier combination is incompatible with another procedure on the claim, rather than conflicting modifiers on one line.
  • N13 (Payment based on professional/technical component modifier(s).): Payment was based on professional or technical component modifiers.
  • N56 (Procedure code billed is not correct/valid for the services billed or the date of service billed.): The procedure code itself is not valid for the service or date.

N519 FAQ

What are examples of invalid combinations?

Common ones are the professional component modifier 26 with the technical component modifier TC, or the side modifiers RT and LT on the same line. Other conflicts depend on the payer's edits.

How do I bill both sides of the body?

Payers differ. Some want modifier 50 on one line, some want RT and LT on separate lines, and some want units. Follow the payer's bilateral billing rules.

Does modifier order matter?

Payers often want pricing modifiers first, but order alone rarely makes a combination invalid. N519 usually means the modifiers conflict in meaning.