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N846 Remark Code: NDC Doesn't Match HCPCS Billed

N846 means the National Drug Code (NDC) reported on the line doesn't correspond to the HCPCS or procedure code billed. The payer checked its NDC-to-HCPCS crosswalk and found the drug product and the billing code don't belong together.

Quick facts

Code
N846 (RARC N846)
Status
Active In use since March 1, 2021.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The drug line was denied for a coding mismatch. It's a provider correction and isn't billable to the patient.
Official description
National Drug Code (NDC) supplied does not correspond to the HCPCs/CPT billed.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What N846 means

A drug line carries two identifiers: the HCPCS code, which defines what is being billed and how many units, and the NDC, which identifies the exact product from the package. Payers cross-check them. N846 appears when the NDC points to a product that isn’t billable under the HCPCS code on the line.

The app guidance for this code is to correct the NDC-to-HCPCS mapping and refile. The line usually comes back with CARC 16.

Common causes

  • Wrong HCPCS for the product. Common with biosimilars and drugs that have product-specific codes.
  • Stale NDC in the charge master. The practice switched suppliers or package sizes, but the drug file still carries the old NDC.
  • NDC of a different strength or formulation than the one given.
  • Unclassified drug code billed when a specific HCPCS code exists for the product, or the other way round.
  • Crosswalk update lag, where a new product isn’t yet in the payer’s table.

How to fix it

  1. Confirm what was administered from the administration record and the package or lot information.
  2. Check the crosswalk the payer uses for that NDC and date of service.
  3. Correct the HCPCS code or the NDC, and recalculate HCPCS units in box 24G and the NDC quantity if either changed.
  4. Submit a corrected claim with resubmission code 7 in box 22.
  5. If the pairing is correct but missing from the payer’s table, contact the payer with product information and ask for reprocessing.

How to prevent it

  • Maintain one drug master that links each NDC stocked to its HCPCS code and units.
  • Update the master whenever inventory changes to a new NDC.
  • Use Claims Validator to check NDC and HCPCS pairs before submission.

Codes that may appear with N846

  • CO-16 (Claim/service lacks information or has submission/billing error(s).): A billing error; N846 identifies the NDC and HCPCS mismatch.
  • CO-4 (The procedure code is inconsistent with the modifier used.): Some payers treat the mismatch as a code-consistency error.
  • M119 (Missing/incomplete/invalid/ deactivated/withdrawn National Drug Code (NDC).): The NDC is missing, invalid, deactivated, or withdrawn.
  • N847 (National Drug Code (NDC) billed is obsolete.): The NDC billed is obsolete.
  • N848 (National Drug Code (NDC) billed cannot be associated with a product.): The NDC can't be associated with any product.
  • N815 (Missing/Incomplete/Invalid NDC Unit Count): The NDC quantity is missing or invalid.

N846 FAQ

What is an NDC-to-HCPCS crosswalk?

It's a table linking drug products (NDCs) to the HCPCS codes they may be billed under. CMS publishes one for Medicare Part B drugs, and many payers use it or their own.

What causes a mismatch?

Common causes are billing the wrong HCPCS for the drug, recording the NDC of a different product or strength, or giving a biosimilar or generic whose NDC maps to a different code.

Which one do I change, the NDC or the HCPCS?

Whichever is wrong. Start from the product actually administered, then choose the HCPCS code that describes it.