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N328 Remark Code: Oxygen Saturation Test Date Issue

N328 means the date of the oxygen saturation test (the oximetry or blood gas study that supports home oxygen) was missing, incomplete, or invalid on the claim or its supporting certification, so the payer could not confirm the qualifying test.

Quick facts

Code
N328 (RARC N328)
Status
Active In use since December 2, 2004.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The oxygen claim was denied because a required test date was absent or unusable. The supplier corrects the data; the patient is not responsible.
Official description
Missing/incomplete/invalid Oxygen Saturation Test date.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What N328 means

Home oxygen coverage generally depends on a documented low blood oxygen reading. N328 tells a DME supplier that the date of that oxygen saturation test was not on the claim, was only partly filled in, or did not make sense (for example, a future date or one that falls after the oxygen billing period). Without it the payer cannot tie the equipment to a qualifying study.

Expect N328 alongside CARC 16 on a line for oxygen equipment or contents. Some payers pair it with CARC 252 when they want the test result sent as documentation.

Common causes

  • The test date was captured on the physician’s paperwork but never transferred into the claim or certification data.
  • The supplier used the order date or delivery date instead of the actual test date.
  • The recorded test was too old for the payer’s policy, so the date was rejected as invalid.
  • Recertification was due and the supplier reused the original test date instead of reporting a newer study where one was required.

How to fix it

  1. Pull the oximetry or blood gas report from the ordering practitioner and read the actual performance date on it.
  2. Compare that date with the payer’s oxygen policy: timing relative to the start of therapy, and whether the test was done at rest, during exercise, or during sleep.
  3. Enter the correct date wherever the payer expects it, which may be the certification data, claim supplemental fields, or an attachment. Payer requirements differ, so follow its DME billing instructions.
  4. Resubmit the line as a corrected claim with frequency code 7 referencing the original claim, or as a new claim if the first one was rejected rather than processed.
  5. If the test truly falls outside policy, a new qualifying test and updated order will be needed before billing future months.

How to prevent it

Build an intake checklist for oxygen referrals that requires the test report itself, not just a statement that a test occurred. Record the test date in its own field and flag any setup where the test date is missing or older than the payer allows. Track recertification due dates so a fresh test is on file before the next billing cycle.

Codes that may appear with N328

  • CO-16 (Claim/service lacks information or has submission/billing error(s).): Claim information is missing or wrong; N328 names the saturation test date.
  • CO-252 (An attachment/other documentation is required to adjudicate this claim/service.): Documentation is required to adjudicate; the payer wants the qualifying test and its date supported.
  • M19 (Missing oxygen certification/re-certification.): Used when the oxygen certification or recertification itself is missing, not just the test date.
  • N234 (Incomplete/invalid oxygen certification/re-certification.): Used when the oxygen certification was received but is incomplete or invalid.
  • N331 (Missing/incomplete/invalid physician order date.): Addresses a missing or invalid physician order date, another date DME suppliers must report.

N328 FAQ

What test does N328 refer to?

It refers to the blood oxygen measurement that qualifies the patient for home oxygen, usually pulse oximetry or an arterial blood gas study. The payer needs the date that test was performed.

Can the test date be after the oxygen was delivered?

Payers generally expect the qualifying test to precede or fall within a defined window around the start of oxygen therapy. The exact window depends on the payer's coverage policy, so check it before correcting the date.

Will changing the date fix the denial?

Only if the correct date was simply entered wrong. If the test was never done or was done outside the payer's window, correcting the field will not create coverage.