CO-266 Denial Code (CARC 266) 2026: Compound Preparation Cost Adjustment

The CO-266 denial code means a plan reduced or refused the compound preparation cost a pharmacy billed on a compounded drug claim. The ingredients may still pay. Only the extra preparation amount is cut. The fix is to check the plan’s compound rules and contract, then write off or appeal the preparation cost. (Primary source: X12 Claim Adjustment Reason Codes)

In brief: reason code 266 reads “Adjustment for compound preparation cost. Usage: To be used for pharmaceuticals only.” Under Part D, mixing work is part of the dispensing fee. So a separate preparation charge is often cut. With group CO, the pharmacy owns that amount.

Part of our denial codes library. Written by Manikandan J, CPC, CRCR, who has reviewed compounding pharmacy remits and ingredient cost appeals for independent pharmacies. Published 3 November 2026. Last updated: 3 November 2026. Code wording quoted word for word from X12. Read about the author and our editorial policy, or contact us to report an error.

What does denial code CO-266 mean?

Denial code CO-266 means the plan adjusted the compound preparation cost on a pharmacy claim. The pharmacy sent that cost as an other amount with qualifier 09. The plan paid less than billed, or nothing. CO tells you the difference is a contractual write-off for the pharmacy.

Source: X12 Claim Adjustment Reason Codes, checked 3 November 2026. On the NCPDP D.0 claim, qualifier 09 in field 479-H8 means compound preparation cost submitted, with the amount in 480-H9 (Nebraska Medicaid D.0 payer sheet).

Methodology: the code wording is copied from the X12 list, and the dispensing fee and field details come from the eCFR and payer sheet cited below.

Key terms: A compound is a drug the pharmacy mixes from two or more ingredients. The dispensing fee is the plan’s set payment for filling a prescription. CO means contractual obligation, so the pharmacy owns the balance.

CO-266 vs OA-266: which one did you get?

CO-266 means your contract with the plan does not pay the compound preparation cost. OA-266 means the cost was adjusted for some other reason, such as a secondary plan following the primary result. Both versions keep the amount off the patient bill. The posting step differs only slightly.

From my compounding audits, CO-266 often hits topical compounds where the plan pays a higher compound dispensing fee instead.

Why do plans cut compound preparation costs?

Plans cut compound preparation costs because mixing work is usually paid through the dispensing fee. The Part D rule in 42 CFR 423.100 lists measurement or mixing of the drug among dispensing fee costs (eCFR, 42 CFR 423.100). So a separate qualifier 09 line is often not paid.

Some commercial and Medicaid plans pay a compound fee or a higher dispensing fee for compounds. Others limit which compounds they cover at all. For instance, a plan may pay only listed ingredients and cut the rest.

How do I fix a CO-266 adjustment?

To fix a CO-266 adjustment, first confirm the prep amount matches what you sent with qualifier 09. Then compare the plan’s compound dispensing fee with your contract. If the fee already covers mixing, write off the cut. Appeal only when the contract names a separate preparation payment.

1. Match qualifier 09. The CO-266 amount should equal the 480-H9 value you sent.
2. Check the compound rules. Read the payer sheet for compound fees and covered ingredients.
3. Read the contract. Look for a separate compound or preparation payment term.
4. Post or appeal. Write it off as contractual, or appeal with the contract page.
5. Update the billing profile. Stop sending qualifier 09 to plans that never pay it.

Claim form note

No claim form visual is shown here. CARC 266 is for pharmaceuticals only. Compound preparation cost is claimed on the NCPDP pharmacy claim, so there is no CMS-1500 box or UB-04 form locator to fix.

Can the patient be billed for a CO-266 amount?

No, the patient cannot be billed for a CO-266 amount on that claim. CO means the contract assigns the cost to the pharmacy. The patient owes only the copay or coinsurance the plan returned. Any cash price for an uncovered compound needs a separate, clear agreement with the patient.

Related codes

FAQ

Sources

How we checked: the CARC 266 quote was matched word for word with the X12 CARC list on 3 November 2026, and the dispensing fee text with the eCFR.

• X12, Claim Adjustment Reason Codes (CARC 266). Accessed 3 Nov 2026.
• eCFR, 42 CFR 423.100 (dispensing fees definition). Accessed 3 Nov 2026.
• Nebraska Medicaid, NCPDP D.0 payer specification. Accessed 3 Nov 2026.
• X12, Claim Adjustment Group Codes. Accessed 3 Nov 2026.

Last updated: 3 November 2026 · Educational content; not legal advice.