OA 300 denial code

Claim adjustment reason code 300. Often reported as OA 300 or CO 300.

Medical plan forwarded to behavioral plan

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 300 means

The medical plan found no benefit for the service and forwarded the claim to the patient's behavioral health plan.

Many plans carve out mental health and substance use services to a separate behavioral health vendor. Here the medical payer passed the claim to that plan for you. Code 301 is used when it is not forwarded.

Behavioral health plans may have their own authorization and network rules.

Group codes seen with 300

On a remittance, 300 comes after a group code. These are the ones it is most often reported with:

• OA 300 (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.
• CO 300 (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.

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

• Behavioral health services were billed to the medical plan.
• The plan carves out behavioral health to a separate vendor.
• The diagnosis on the claim placed the service under behavioral health benefits.

What to do next

1. Record that the claim was forwarded to the behavioral health plan.
2. Follow up with the behavioral health plan for its decision.
3. Check that you are in network and have any needed authorization with that plan.

Related codes

• 301 (reason code) Medical plan: bill the behavioral plan