Denial codes · Denial code
CO-22 on a nutrition claim: another plan should pay first
By Javier Alvarez · Updated · 4 min read
| Official description | This care may be covered by another payer per coordination of benefits. |
|---|---|
| Group code | CO: not billable to the patient while COB is unresolved |
| Common remark codes | N598, MA04, N479, N4, MA92, N245 |
| Who updates COB | Usually the member, by phone or portal with the plan |
| Fix route | Bill the primary; then a secondary claim with the primary's adjudication |
| Medicare | Medicare Secondary Payer rules decide when Medicare pays second |
CO-22 is a routing problem between two insurance plans. The payer that got your claim is saying: "we think somebody else pays first." Sometimes that is true (the patient has a spouse's plan, or Medicare plus an employer plan). Just as often the payer's records are stale, and the patient has to fix them. Either way, the fix starts with one phone call, not an appeal.
What CO-22 means (official X12 wording)
The X12 Claim Adjustment Reason Code list defines CARC 22 as:
"This care may be covered by another payer per coordination of benefits."
Coordination of benefits (COB) is the set of rules that decides which plan pays first when a person has more than one. The primary pays under its own terms; the secondary then looks at what is left. When the payer that received your claim has a record of other coverage it believes is primary, it denies with CO-22.
Remark codes you may see with CO-22
| Remark code | Official X12 description | What it tells you |
|---|---|---|
| N598 | "Health care policy coverage is primary." | The payer has another policy on file as primary |
| MA04 | "Secondary payment cannot be considered without the identity of or payment information from the primary payer. The information was either not reported or was illegible." | You billed as secondary without the primary's info |
| N479 | "Missing Explanation of Benefits (Coordination of Benefits or Medicare Secondary Payer)." | Attach or include the primary's EOB |
| N4 | "Missing/Incomplete/Invalid prior Insurance Carrier(s) EOB." | The primary EOB data is missing or unusable |
| MA92 / N245 | "Missing plan information for other insurance." / "Incomplete/invalid plan information for other insurance." | The other-payer fields on your claim are empty or wrong |
The usual causes on nutrition claims
1. The patient has two plans and you billed the secondary
The most common case: the patient handed you one card, you billed it, and that plan knows about another one that is primary. Typical pairs: an employer plan plus a spouse's employer plan; a child on both parents' plans; Medicare plus an employer group plan. For children covered by both parents, many plans use the "birthday rule" (the parent whose birthday falls earlier in the calendar year has the primary plan), but custody arrangements and plan terms can change the order.
2. The payer's COB record is stale
The patient left a job or dropped a spouse's plan, but the payer still has the old coverage on file. Many plans also ask members to confirm other coverage periodically, and an unanswered questionnaire can put claims on hold with CO-22. Only the member can usually fix this, by calling member services or updating COB in the plan's portal.
3. Medicare and another plan, in the wrong order
Whether Medicare pays first depends on things like employer size and why the person has Medicare. CMS publishes the rules under Medicare Secondary Payer; Medicare.gov's summary is the easiest starting point. For a Medicare MNT patient who is still working with employer coverage, the employer plan may be primary, and its nutrition benefit (not Medicare's diabetes/CKD rules) applies first.
4. A secondary claim without the primary's data
You did bill the primary first, but the secondary claim went out without the other-payer information: payer name and ID, paid amount, and the primary's adjustments. That comes back as CO-22 with MA04, N479 or N4.
How to fix a CO-22
- Confirm which plan is primary. Call the payer that denied and ask what other coverage it has on file (plan name, effective dates). Then ask the patient.
- If the other coverage is real and primary: send a new claim to the primary plan. Its timely-filing clock runs from the date of service, so do it right away. When the primary pays or denies, send the claim to the secondary with the primary's adjudication (the 837P other-payer loops, or the primary's EOB on paper).
- If the other coverage ended or is wrong: ask the patient to call member services and update COB. Then call the payer and ask it to reprocess the original claim. Some payers reprocess on their own after the update; others want a corrected claim (frequency code 7). Ask which.
- If you billed as secondary without primary data: send a corrected claim with the complete other-payer information.
- Keep the CO-22 remit. It shows you filed within the window if the primary later questions timing.
How to prevent CO-22
- Ask about all coverage at intake. "Do you, a spouse or a parent have any other health insurance, including Medicare or Medicaid?" should be on every intake form, and on the benefits verification checklist you use when you call the payer.
- Run an eligibility check before the first visit. A 270/271 eligibility check sometimes returns other-coverage information; when it does, act on it.
- Re-ask every January and whenever the patient changes jobs or marital status.
- Store both cards and the order of coverage in the patient record, so every claim goes to the right payer first.
- Coach the patient. If the payer says COB is outdated, give the patient the exact words: "Please update my coordination of benefits; I have no other coverage since [date]."
For the full list of codes on a nutrition remit, go back to the denial code lookup. To read the primary's EOB before you bill the secondary, see How to read an ERA/EOB.