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N518 Remark Code: Oxygen Accessories Not Paid Separately

N518 means the payer does not make a separate payment for accessories furnished for use with oxygen equipment. Items like tubing, cannulas, or masks used with the oxygen system are treated as included in the payment for the oxygen equipment.

Quick facts

Code
N518 (RARC N518)
Status
Active In use since March 1, 2009.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The accessory charge is included in the oxygen equipment payment. Under most contracts, including Medicare assignment, the supplier cannot bill the patient for it.
Official description
No separate payment for accessories when furnished for use with oxygen equipment.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What N518 means

Home oxygen is usually paid as a bundled service: the payment for the oxygen equipment is meant to cover the system and the items needed to use it. N518 tells a supplier it billed one of those items, such as a cannula, tubing, a mask, or another accessory, as a separate line, and the payer will not pay it on its own.

It commonly appears with CARC 97 (included in another service’s payment) or CARC 234 (not paid separately).

Common causes

  • A billing system set to generate supply lines automatically for oxygen patients.
  • Accessory HCPCS codes billed along with the oxygen rental for the same period.
  • Confusion between payers: one plan may allow a separate accessory while another bundles it.
  • Accessories billed after a change in the patient’s equipment status without checking how the payer handles that status.

How to fix it

  1. Confirm the patient’s oxygen status with the payer: current rental, capped period, or patient-owned equipment.
  2. Read the payer’s oxygen policy for that status and the accessory billed.
  3. Write off the accessory if the policy includes it in the equipment payment.
  4. Appeal if the policy allows separate payment in the patient’s situation and the payer applied the bundling rule incorrectly. Include documentation of the equipment status.
  5. Correct future claims so the accessory is not billed separately for that payer and status.

How to prevent it

Set payer-specific rules in your billing system so oxygen accessory codes are suppressed when the payer bundles them. Review the rules whenever a payer updates its oxygen policy or a patient’s equipment status changes.

Codes that may appear with N518

  • CO-97 (The benefit for this service is included in the payment/allowance for another service/procedure that has already been adjudicated.): The accessory is included in the payment for the oxygen equipment.
  • CO-234 (This procedure is not paid separately.): The item is not paid separately.
  • CO-96 (Non-covered charge(s).): Some payers report the accessory as a non-covered charge with this remark.
  • M19 (Missing oxygen certification/re-certification.): Missing oxygen certification or recertification, a documentation issue rather than a bundling one.
  • N234 (Incomplete/invalid oxygen certification/re-certification.): Incomplete or invalid oxygen certification or recertification.
  • M3 (Equipment is the same or similar to equipment already being used.): Equipment is the same as or similar to equipment already in use.

N518 FAQ

Which accessories are considered included?

It depends on the payer's oxygen policy. Medicare's oxygen payment rules, for example, generally treat supplies and accessories used with the oxygen system as included in the monthly payment. Check the payer's policy for the specific item.

What if the patient owns the oxygen equipment?

Some payers handle accessories differently when the patient owns the equipment or when the oxygen rental period has ended. Review the payer's policy and the patient's equipment history.

Can I bill the patient for denied accessories?

Usually not when the adjustment uses group code CO. The payer considers the accessory paid through the equipment allowance.