CO A5 denial code

Claim adjustment reason code A5. Often reported as CO A5 or OA A5.

Medicare PPS capital cost outlier

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 A5 means

Reports the capital cost outlier portion of an inpatient prospective payment system (PPS) claim, not a denial.

A5 is an informational payment code used on inpatient hospital claims paid under a prospective payment system, typically Medicare. It identifies the amount tied to the capital cost outlier calculation, which applies when a stay's costs are far above the normal DRG payment.

Hospital billing and reimbursement staff use it to reconcile outlier payments. A physician or professional biller will rarely see it.

Group codes seen with A5

On a remittance, A5 comes after a group code. These are the ones it is most often reported with:

• CO A5 (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.
• OA A5 (Other Adjustment): Used for adjustments that are neither the provider's contractual write-off nor the patient's share. It often appears with coordination of benefits, for example when another payer already paid.

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 inpatient stay had unusually high costs that qualified for outlier treatment under the PPS formula.
• The payer is breaking out the capital portion of the outlier calculation on the remittance.
• The claim was reprocessed and the capital outlier amount changed.

What to do next

1. Reconcile the capital outlier amount with your expected reimbursement calculation for the stay.
2. Check that covered charges, cost-to-charge ratio and DRG on the claim are correct, since they drive outlier math.
3. Post the amount to the correct contractual or outlier adjustment account per your hospital's posting rules.

Related codes

• A8 (reason code) DRG could not be grouped
• A6 (reason code) Prior stay or 30 day transfer rule not met