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CO-A6 Denial Code: Qualifying Stay or Transfer Rule Unmet

CO-A6 means the patient didn't meet a prior hospitalization or 30-day transfer requirement. It's most common with Medicare skilled nursing facility coverage, which generally requires a 3-day qualifying inpatient stay and admission to the SNF within 30 days of discharge.

Quick facts

Code
CO-A6 (CARC A6)
Status
Active In use since January 1, 1995.
Code set
Claim Adjustment Reason Codes (CARC)
Group codes
  • CO (Contractual Obligation): Under CO the facility absorbs the amount, often because required notices weren't given or the facility is responsible for the error.
  • PR (Patient Responsibility): Often used when the stay isn't covered and the patient received proper notice. The patient may be billed according to program rules.
Official description
Prior hospitalization or 30 day transfer requirement not met.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What CO-A6 means

CARC A6 says prior hospitalization or 30 day transfer requirement not met. Some benefits are available only after a qualifying hospital stay, and only if the patient transfers to the next level of care within a set window. The code is most closely associated with Medicare Part A skilled nursing facility (SNF) coverage.

Under traditional Medicare, SNF coverage generally requires a qualifying inpatient hospital stay of at least three consecutive days, not counting the discharge day, followed by SNF admission within 30 days of hospital discharge. If the payer’s records don’t show both, the SNF claim is denied with A6.

The most common trap is observation status. A patient may spend several nights in the hospital but be classified as an outpatient under observation for part or all of the time. Those days don’t count toward the three inpatient days.

Common causes

  • Observation days counted as inpatient by the SNF during admission screening.
  • Inpatient stay shorter than three days under the counting rules.
  • SNF admission more than 30 days after hospital discharge without an applicable exception.
  • Qualifying stay dates missing or wrong on the SNF claim (N173).
  • Plan without a waiver, when staff assumed a Medicare Advantage or program waiver applied.

How to fix it

  1. Get the hospital’s admission and discharge records and confirm inpatient order dates, not just arrival and departure.
  2. Recount inpatient days under Medicare rules.
  3. Correct the qualifying stay dates on the claim if they were wrong, and submit a corrected institutional claim.
  4. Check waivers for Medicare Advantage or other programs and cite them in an appeal if they apply.
  5. Review notices. Whether the patient can be billed depends on whether required liability notices were given before care.

How to prevent it

  • Verify inpatient status and dates with the hospital before accepting an SNF admission.
  • Confirm plan waivers in writing during admission screening.
  • Track the 30-day transfer window for patients coming from hospitals.
  • Give required notices when coverage is uncertain. See eligibility and COB denials.

Specialty notes

Skilled nursing facilities and swing-bed hospitals see A6 most. Hospital case managers can reduce these denials by telling patients and SNFs clearly when a stay is observation rather than inpatient.

Remark codes that may appear with CO-A6

  • N173 (No qualifying hospital stay dates were provided for this episode of care.): No qualifying hospital stay dates were provided for this episode of care.
  • CO-190 (Payment is included in the allowance for a Skilled Nursing Facility (SNF) qualified stay.): Payment included in the allowance for a skilled nursing facility qualified stay.
  • CO-272 (Coverage/program guidelines were not met.): Coverage or program guidelines weren't met.
  • CO-177 (Patient has not met the required eligibility requirements.): Patient hasn't met the required eligibility requirements.
  • CO-50 (These are non-covered services because this is not deemed a 'medical necessity' by the payer.): Not medically necessary, another common reason SNF stays are denied.

CO-A6 FAQ

What is the Medicare 3-day rule for SNF coverage?

Traditional Medicare generally covers SNF care only after an inpatient hospital stay of at least three consecutive days, counting the admission day but not the discharge day. Observation days and emergency department time don't count as inpatient days.

What is the 30-day transfer requirement?

Generally, the patient must be admitted to the SNF within 30 days after the qualifying hospital discharge, for a condition treated during that stay or that arose while in the SNF for such a condition. There are limited exceptions.

Do Medicare Advantage plans require a 3-day stay?

Many Medicare Advantage plans waive the 3-day requirement, and some Medicare programs such as certain ACO waivers do too. Check the patient's plan.

How do I report the qualifying stay on the claim?

SNF claims report the qualifying stay dates using the occurrence span code the payer requires. Missing or wrong dates can trigger A6 even when the stay qualified.