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N816 Remark Code: NDC Unit of Measure Missing/Invalid

N816 means the NDC unit of measure on a drug line was missing, incomplete, or invalid. The unit of measure is the qualifier, such as ML for milliliters or UN for units, that tells the payer how the NDC quantity is counted.

Quick facts

Code
N816 (RARC N816)
Status
Active In use since July 1, 2019.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The drug line was denied for a correctable data error. The patient is not responsible.
Official description
Missing/Incomplete/Invalid NDC Unit of Measure
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What N816 means

An NDC quantity is meaningless without its unit: 2 could mean 2 milliliters, 2 grams, or 2 vials. The unit of measure qualifier closes that gap. N816 means the qualifier was absent, cut off, not a recognized value, or didn’t fit the product the payer found for that NDC.

The official code set for this field is short: F2, GR, ME, ML, and UN. N816 usually comes with CARC 16 and is most common on claims to payers that collect NDC detail for drug rebates, such as Medicaid.

Common causes

  • Qualifier omitted in the NDC supplemental data, leaving only the NDC and a number.
  • Wrong unit for the product, such as UN reported for a liquid the payer measures in ML.
  • Free-text units like “mg” or “vial” instead of the two-character qualifier.
  • Clearinghouse formatting that misplaces or truncates the qualifier.

How to fix it

  1. Look up the product by its 11-digit NDC and check how it is packaged and measured.
  2. Choose the correct qualifier, and check the payer’s drug file or policy if it specifies one for that NDC.
  3. Recheck the quantity so it is expressed in that unit. Changing ML to UN without changing the number will produce a new error.
  4. Submit a corrected claim with resubmission code 7 in box 22.

How to prevent it

  • Store the unit of measure with every NDC in your drug master file so it fills automatically.
  • Limit the field to the five valid qualifiers in your billing software.
  • Review NDC edits whenever you switch suppliers or package sizes, since a new NDC may use a different unit.

Codes that may appear with N816

  • CO-16 (Claim/service lacks information or has submission/billing error(s).): The claim lacks information needed for adjudication; N816 names the NDC unit of measure.
  • N815 (Missing/Incomplete/Invalid NDC Unit Count): The NDC quantity itself is missing or invalid.
  • M119 (Missing/incomplete/invalid/ deactivated/withdrawn National Drug Code (NDC).): The NDC number is missing, invalid, or deactivated.
  • N848 (National Drug Code (NDC) billed cannot be associated with a product.): The NDC billed can't be associated with a product.

N816 FAQ

What unit of measure qualifiers are used?

The common ones are F2 (international unit), GR (gram), ME (milligram), ML (milliliter), and UN (unit or each). Payers may limit which ones they accept for particular products.

How do I choose between ML and UN?

Use the unit that matches how the product is measured and packaged. A liquid drawn from a vial is typically measured in ML; a tablet, capsule, or single-use kit is typically counted in UN. Some payers publish a preferred unit per NDC.

Can a valid qualifier still trigger N816?

Yes, if the payer's drug file expects a different unit for that NDC. The qualifier must be both valid and appropriate for the product.