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M99 Remark Code: Missing UPN or Serial Number

M99 means the payer needed a Universal Product Number (UPN) or serial number for the item billed, and it was missing, incomplete, or invalid. Add the correct identifier from the product or invoice and resubmit.

Quick facts

Code
M99 (RARC M99)
Status
Active In use since January 1, 1997; last modified February 28, 2003.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The line was not paid because an item identifier was defective. The provider corrects and resubmits; the patient is not billed.
Official description
Missing/incomplete/invalid Universal Product Number/Serial Number.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What M99 means

HCPCS codes often describe a category of item rather than a specific product. Some payers want to know exactly which product or unit was furnished, particularly for equipment, supplies, and devices. They ask for a Universal Product Number, which identifies the product, or a serial number, which identifies the individual unit.

M99 tells you that identifier was absent, cut off, or not recognised. Because the remark is a data request, the line is typically rejected under CARC 16 and can be paid after correction.

Common causes

  • A payer requirement for product identifiers that is not built into the billing workflow.
  • Identifiers captured at delivery but not transferred to the claim.
  • Typographical errors or truncated numbers.
  • The number placed in the wrong segment of the electronic claim or with the wrong qualifier.
  • A serial number reported for an item that was later swapped at delivery.

How to fix it

  1. Check the payer’s requirements to see whether a UPN, serial number, or both are needed for the item.
  2. Get the identifier from the product packaging, delivery ticket, or invoice.
  3. Enter it in the correct field with the right qualifier.
  4. Resubmit as a new claim if the original was rejected, or a corrected claim with frequency code 7 if it was adjudicated.

How to prevent it

  • Capture UPN and serial numbers at dispensing or delivery, and carry them to the claim.
  • Maintain a list of items and payers that require identifiers.
  • Use a Claims Validator to flag items that need product identifiers before submission.

See the CO-16 guide for related information rejections.

Codes that may appear with M99

  • CO-16 (Claim/service lacks information or has submission/billing error(s).): The claim lacks information, and M99 identifies the product or serial number as missing.
  • M119 (Missing/incomplete/invalid/ deactivated/withdrawn National Drug Code (NDC).): The drug equivalent: a missing or invalid National Drug Code.
  • N350 (Missing/incomplete/invalid description of service for a Not Otherwise Classified (NOC) code or for an Unlisted/By Report procedure.): Asks for a description of an item billed under a not otherwise classified code.

M99 FAQ

What is a Universal Product Number?

A standardized product identifier, such as a barcode-based number, assigned by the manufacturer to a specific item. Some payers use it to identify supplies and devices precisely.

When is a serial number required?

Payers may require serial numbers for certain durable medical equipment, implants, or high-value items so they can track the specific unit furnished.

Where do I report these numbers?

In the electronic claim's line-level product identification fields, or where the payer's paper claim instructions specify. Requirements vary by payer.