Look up another code

CO-80 Denial Code (Deactivated): Outlier Days

CO-80 reported the number of outlier days on an inpatient claim. X12 deactivated it because that count is carried in the 835's QTY segment with qualifier OU; the day outlier dollar amount has its own code, CARC 69.

X12 deactivated CARC80 on October 16, 2003. Payers should no longer use it on new remittances, but it can still appear on older ERAs, corrected claims, and appeals.

Code: CO-80 (CARC 80)
Status: Deactivated StoppedOctober 16, 2003 (in use since January 1, 1995).
Code set: Claim Adjustment Reason Codes (CARC)
Group codes: CO (Contractual Obligation): Shown on hospital remittances as a quantity, separate from any payment adjustment.
Official description: Outlier days. (Handled in QTY, QTY01=OU)
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What CO-80 meant

Some inpatient payment systems pay extra when a stay runs well beyond the expected length for its DRG. The days beyond that threshold are outlier days. CARC 80 showed how many such days the payer recognized on a claim, which let hospitals check the payer’s calculation.

What replaced it

There is no replacement reason code. The official text says outlier days are handled in QTY with qualifier OU, which is where the count appears on current remittances. The money connected to those days is reported with CO-69, the active day outlier amount code. Cost-based outliers use CO-70, and Medicare capital cost outliers use CO-A5.

If you still see CO-80

It is found only in archived institutional payments. When auditing old outlier payments, pair the CO-80 day count with the matching outlier dollars to confirm the calculation. Never post the day count as a dollar adjustment. For current claims, compare the QTY outlier days with your length-of-stay data and the DRG’s threshold; if they disagree, ask the payer how it determined the threshold.

CO-69 (Day outlier amount.): Day outlier amount, the active code for the dollars tied to outlier days.
CO-70 (Cost outlier - Adjustment to compensate for additional costs.): Cost outlier adjustment, the cost-based counterpart.
CO-A5 (Medicare Claim PPS Capital Cost Outlier Amount.): Medicare PPS capital cost outlier amount.

CO-80 FAQ

How is CO-80 different from CO-69?

CO-80 counted the days that qualified as outlier days. CO-69, which is still active, reports the dollar amount associated with day outliers.

Where is the outlier day count now?

In the claim's supplemental quantity segment, QTY with qualifier OU, as the code's official text indicates.

Important: read before using this information

This page is general educational information about a standard industry code set. It is not medical billing, coding, legal, reimbursement, or compliance advice, and it does not create a professional or advisory relationship with ClaimsRevenue.

Code definitions, payer usage, contracts, and laws change, and payers may apply the same code differently. The information is provided “as is,” without warranties of any kind, express or implied, including accuracy, completeness, or currency. You are solely responsible for verifying it against the current official X12 code lists, CMS guidance, your payer contracts, and payer policies before relying on it, and for every billing, coding, collection, and appeal decision you make.

Using this information does not guarantee that any claim will be paid or that any appeal will succeed. To the fullest extent permitted by law, ClaimsRevenue and MOODRX LLC are not liable for any loss or damage arising from its use. Official code descriptions are published by X12 and are quoted for reference only. See our full Claims Validation Disclaimer.