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N306 Remark Code: Acute Manifestation Date Invalid

N306 means the acute manifestation date was missing, incomplete, or invalid. That is the date a chronic condition flared up into an acute episode, which some payers require to support treatment such as chiropractic manipulation.

Quick facts

Code
N306 (RARC N306)
Status
Active In use since December 2, 2004.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The provider must supply a valid date; the adjustment is not patient responsibility while the claim is correctable.
Official description
Missing/incomplete/invalid acute manifestation date.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What N306 means

Many payers cover treatment for chronic conditions only when an acute exacerbation is present, or they treat acute and maintenance care differently. The acute manifestation date tells the payer when the chronic condition became acute. N306 says that date was missing or didn’t pass the payer’s edits.

It often comes with CARC 16. Because the date can affect whether the payer considers the care active treatment, fixing it accurately matters; guessing a date to get past the edit can create documentation problems later.

Where the problem usually starts

  1. The date isn’t captured clinically. Notes describe a flare-up but never record a date.
  2. It isn’t transferred to billing. The date exists in the note but not in the claim’s date fields.
  3. Wrong qualifier. The date is entered in box 15 with a qualifier for initial treatment or a latest visit.
  4. It conflicts with other dates. An acute manifestation date after the date of service, or years in the past for an episode described as recent.

How to fix it

  1. Review the treating provider’s documentation for when the acute episode began.
  2. If the date is documented, report it with the qualifier for acute manifestation in box 15 or the electronic equivalent.
  3. If it isn’t documented, ask the clinician; don’t infer a date that the record doesn’t support.
  4. Confirm the date is on or before the date of service.
  5. Resubmit a corrected claim with frequency code 7.

How to prevent it

Add an acute manifestation date field to the initial visit template for chronic-condition episodes, especially in chiropractic and therapy settings. Map that field to the claim automatically, and edit for a missing date on payers that require it. For how clinical documentation gaps turn into denials, see our CARC 16 guide.

Codes that may appear with N306

  • CO-16 (Claim/service lacks information or has submission/billing error(s).): Missing or invalid information; N306 names the acute manifestation date.
  • CO-50 (These are non-covered services because this is not deemed a 'medical necessity' by the payer.): May follow on review if the documentation doesn't support an acute episode.
  • N326 (Missing/incomplete/invalid last x-ray date.): The last x-ray date is missing or invalid, another date often required on chiropractic claims.
  • M122 (Missing/incomplete/invalid level of subluxation.): The level of subluxation is missing or invalid.
  • N314 (Missing/incomplete/invalid diagnosis date.): The diagnosis date is missing or invalid.

N306 FAQ

Where does the acute manifestation date go?

On the CMS-1500 it can be reported in box 15 with the qualifier for acute manifestation of a chronic condition. Electronic claims have a matching date field. Some payers give their own instructions.

Who needs to report it?

Chiropractors see this requirement most often, but any payer that distinguishes acute episodes from ongoing chronic care may ask for it.

Is it the same as the onset date?

No. The onset date is when a condition first began. The acute manifestation date is when a chronic condition flared up.