CO-22 on a dental claim: coordination of benefits, and which plan is primary
CO-22: This care may be covered by another payer under coordination of benefits. What it means on a dental claim, why dental offices get it, what to do, and whether the patient owes it.
By Dr. Salem Sayegh, general dentist, Glendora, California ·
The short answer: CO-22 means the payer believes another plan should pay first, under coordination of benefits. It is common when a patient has two dental plans, or when the payer’s records still show other coverage that has ended. Confirm which plan is primary, update both payers and your software, and rebill in the right order.
| Code | CO-22 (adjustment reason code) |
|---|---|
| Group | CO, contractual obligation |
| Meaning | Another payer may be primary |
| Is it a denial? | Yes, until the order of benefits is sorted out |
| Bill the patient? | Not yet. Rebill the right plan first |
| Usually fixable? | Yes |
Why dental offices get CO-22
- The patient has two plans and the claim went to the secondary first.
- A child is covered by both parents, and the birthday rule makes the other parent’s plan primary.
- The payer’s file still shows other coverage that has ended, often because the patient never returned the payer’s coordination of benefits questionnaire.
- The patient has a medical plan with dental benefits, or Medicaid, alongside a commercial dental plan.
What to do about CO-22
- Ask the patient about all coverage, and verify each plan with the payers.
- Work out the order of benefits. For dependent children most plans use the birthday rule: the plan of the parent whose birthday falls earlier in the year pays first.
- If the other coverage has ended, ask the patient to update their coordination of benefits information with the payer.
- Bill the primary, then send the secondary claim with the primary’s EOB attached.
Can you bill the patient for CO-22?
Not yet. Once both plans have processed the claim in the right order, the patient owes whatever remains as patient responsibility.
Questions about a specific EOB line?
Ask Sai Biller, our free dental insurance chatbot. Type the codes and amounts from the line, leave out patient details, and it explains what happened and what to do next. For offices posting every day, Sai for Dentists reads each EOB line as it posts, checks the allowed amount against your contracted fee and lists every denial, downgrade and underpayment for your team.
Sources
- X12 claim adjustment reason codes and remittance advice remark codes. Meanings here are paraphrased; see X12 for the official wording.
- American Dental Association, CDT: Code on Dental Procedures and Nomenclature. Procedure labels here are our own short descriptions.
- Payers apply these codes differently. Your contract and each payer’s provider manual decide what applies to your office.
Common questions
What is the birthday rule for dental insurance?
When a child is covered by both parents’ plans, most plans make the primary the plan of the parent whose birthday (month and day, not year) comes first in the calendar year. Divorce decrees and plan rules can change this.
Why do I get CO-22 when the patient has only one plan?
The payer’s records may still show coverage that has ended. The patient usually has to confirm with the payer, often by returning a coordination of benefits form, before the claim is reprocessed.
Does the secondary dental plan always pay the rest?
No. Many dental plans have non-duplication clauses: the secondary pays only up to what it would have paid as primary, minus what the primary paid, which is often nothing.
