CO A6 denial code

Claim adjustment reason code A6. Often reported as CO A6 or PR A6.

Prior stay or 30 day transfer rule not met

Unofficial reference. This is our own plain-English explanation, not the official code text. Payer rules differ. Verify with the payer and the official X12 code list. AlphaPrefix is not affiliated with X12, CMS or any payer. Data last updated Nov 11, 2026.

What A6 means

The service depends on a qualifying prior hospital stay or a timely transfer, and the payer found that condition was not met.

Some benefits, most often skilled nursing facility care, are only covered when the patient had a qualifying inpatient stay beforehand or moved to the new setting within a set window. A6 tells you the payer could not confirm that link.

The fix usually lies in the dates and the prior stay information on the claim, or in showing that an exception applies under the plan's rules.

Group codes seen with A6

On a remittance, A6 comes after a group code. These are the ones it is most often reported with:

• CO A6 (Contractual Obligation): The provider's side of the ledger. The reduction comes from the payer contract or a rule the provider has to follow, and the patient normally cannot be billed for it.
• PR A6 (Patient Responsibility): The amount is assigned to the patient. Deductibles, coinsurance and copays are the everyday examples. Whether you can collect it still depends on your contract and the patient's plan.

The payer chooses the group code for each adjustment, so the same reason code can appear with another group code on your remittance. Read the two together. More about group codes.

Common causes

• The patient's earlier hospital stay was too short or was billed as outpatient or observation.
• The admission to the next setting happened after the allowed transfer window.
• The qualifying stay dates were missing or wrong on the claim.

What to do next

1. Verify the dates and status of the prior hospital stay with the discharging facility.
2. Correct the qualifying stay or occurrence span information on the claim and resubmit if it was wrong.
3. Check the payer's policy for waivers or exceptions that may apply to this patient.
4. Review whether the patient was given advance notice of possible financial liability before services.

Related codes

• A5 (reason code) Medicare PPS capital cost outlier
• B15 (reason code) Qualifying service not received