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M24 Remark Code: Doses per Vial Missing or Invalid

M24 means the claim for a drug did not include a valid number of doses per vial. The payer needs it to calculate how much drug was supplied and what to pay.

Quick facts

Code
M24 (RARC M24)
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 drug line is unpaid until the quantity detail is corrected. It is not billed to the patient.
Official description
Missing/incomplete/invalid number of doses per vial.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What M24 means

Injectable drugs are billed in HCPCS units, but they come in vials of different sizes. For some drugs, particularly those billed per vial or by dose, the payer needs to know how many doses one vial contains to check the math. M24 says that number was missing or not valid.

It is a drug billing data remark and nearly always travels with CARC 16.

Common causes

  • The drug detail segment was left blank on the claim.
  • Units were reported in milligrams when the payer expected vials, or the reverse.
  • The NDC unit of measure and quantity did not match the HCPCS units.
  • Multi-dose vials were billed without explaining how many doses were drawn.

How to fix it

  1. Check the package insert or label for the vial size and doses per vial.
  2. Recalculate units so the HCPCS units (box 24G), NDC quantity, and doses per vial agree.
  3. Add the missing detail in the field the payer requires.
  4. Resubmit as a corrected claim with resubmission code 7, or as a new claim if the payer returned it unprocessed.

How to prevent it

Keep a drug master list with HCPCS code, NDC, vial size, and billing unit conversion for every drug you stock. See MUE and units of service denials for more on units errors.

Codes that may appear with M24

  • CO-16 (Claim/service lacks information or has submission/billing error(s).): Information needed to price the drug is missing or invalid.
  • CO-252 (An attachment/other documentation is required to adjudicate this claim/service.): Some payers request the invoice or drug documentation to confirm the quantity supplied.
  • N362 (The number of Days or Units of Service exceeds our acceptable maximum.): Units billed exceed the payer's acceptable maximum.
  • M20 (Missing/incomplete/invalid HCPCS.): The HCPCS code for the drug itself is missing or invalid.
  • N350 (Missing/incomplete/invalid description of service for a Not Otherwise Classified (NOC) code or for an Unlisted/By Report procedure.): The description of a not otherwise classified drug is missing.

M24 FAQ

Where do I report doses per vial?

It depends on the payer. Many want drug detail in the NDC and quantity fields or in the shaded area of box 24 and box 19 on the CMS-1500. Check the payer's drug billing instructions.

Does M24 relate to NDC reporting?

Often. Payers use the NDC, unit of measure, and quantity to understand the package, and missing pieces can trigger M24.

What about wasted drug from a single-dose vial?

Some payers, including Medicare, require the JW or JZ modifier to report discarded or no discarded amounts. That is separate from doses per vial but affects the same line.