A 67-year-old patient comes in for a 99214 visit. The front desk scans her Medicare card, the claim goes to Medicare, and three weeks later it comes back denied with CO-22: this care may be covered by another payer per coordination of benefits. The biller calls the patient, learns that she still works and has coverage through her employer, bills the employer plan, waits for that remittance, and then bills Medicare as secondary. The visit was in March. Medicare pays in June.
Coordination of benefits denials are the most preventable category on most denial reports, because the information that would have prevented them was available at the front desk on the day of the visit. Nobody asked. Or somebody asked once, in 2022, and the answer has been copied forward ever since.
This article is about how these denials happen, what Medicare and other payers expect a practice to know, and the registration changes that make CO-22 rare.
Key takeaways
- CO-22 means the claim was fine and the order of payers was wrong. The fix is upstream, at registration, not in the billing office.
- For Medicare patients, the deciding question is current employment (the patient's or a spouse's), not whether they have another card. Retiree coverage is secondary; employer coverage from a job someone still holds is usually primary.
- Ask four short questions at every visit and record the answers with a date. "No changes" is an answer, not an assumption.
- The 271 eligibility response often already names the other payer. Train the front desk to read past "active".
- When the payer's file is wrong, the patient or employer has to fix it with the Benefits Coordination and Recovery Center; hold the claim and document the date rather than resubmitting into the same denial.
What the codes are telling you
| Code | Meaning | Usual cause |
|---|---|---|
| CO-22 | This care may be covered by another payer per coordination of benefits | Payer's records show another plan is primary |
| CO-16 with remark MA04 or N4 | Secondary payment cannot be considered without the identity of or payment information from the primary payer | Claim sent to the secondary without primary payment details |
| OA-23 | The impact of prior payer adjudication, including payments and adjustments | Not a denial; the secondary is showing what the primary already covered |
| CO-109 | Claim not covered by this payer or contractor | Wrong payer entirely, often a Medicare Advantage plan billed to Medicare or the reverse |
CO-22 is the one to work upstream. When Medicare issues it, its records at the Benefits Coordination and Recovery Center show another insurer as primary. When a commercial plan issues it, the plan believes another plan, often a spouse's, is primary under the order-of-benefits rules. Either way the claim itself was fine. The order of payers was wrong.
The order-of-benefits rules that cause the most trouble
For Medicare, the Medicare Secondary Payer rules decide when Medicare pays second. The situations a physician office meets most often:
- Working aged. A patient 65 or older covered by an employer group health plan through their own or a spouse's current employment, where the employer has 20 or more employees. The group plan is primary; Medicare is secondary.
- Disability. A patient under 65 with Medicare due to disability, covered by a large group health plan (100 or more employees) through their own or a family member's current employment. The group plan is primary.
- End-stage renal disease. During a 30-month coordination period, the group health plan is primary regardless of employer size.
- Accidents and injuries. Workers' compensation, no-fault auto and liability insurance are primary for the related care. Medicare may make a conditional payment, but the claim needs the accident information.
- Retiree coverage. A retiree plan is secondary to Medicare. Many patients describe retiree coverage as "my work insurance," which is why the question has to be about current employment, not about having a card.
Two of these deserve a second look because they are where small practices get it backwards. A 68-year-old whose spouse works for a 12-person company has employer coverage, but the employer is under 20 employees, so Medicare is primary and the employer plan pays second. A 58-year-old on Medicare for disability whose spouse works for a 60-person company is in the same position: the employer is under 100, so Medicare is primary. The employer size question is one the front desk cannot answer and should not try to; the eligibility response and the payers' own records settle it, and the practice's job is to record what the patient says and compare.
For commercial plans covering dependents, the birthday rule is the one most practices get wrong: when a child is covered by both parents' plans, the plan of the parent whose birthday falls earlier in the calendar year is usually primary. The year of birth does not matter, only the month and day. Divorce decrees and court orders can override this, and the plans themselves will tell you what they have on file if you ask.
Medicaid is the payer of last resort in every state. If a Medicaid patient has any other coverage, that coverage is billed first.
The questions to ask, and how often
Hospitals are required to ask Medicare patients a set of Medicare Secondary Payer questions at regular intervals. Physician practices are not held to the same requirement, but the questions are the right ones, and asking them is how a practice keeps its records correct. We use a short version at every visit for patients with Medicare, and a version of the last two for everyone:
- Are you or your spouse currently working? If yes, do you have health coverage through that employer?
- Is today's visit related to an accident, an injury at work, or a condition someone else may be responsible for?
- Do you have any other health insurance, including through a spouse or a parent? May we see the card?
- Has your insurance changed since your last visit?
Two minutes at check-in. The answers go into the registration record with the date they were asked, and "no changes" is recorded as an answer, not assumed. Put the four questions on the check-in screen or the intake tablet so they are asked the same way every time, and give the front desk one rule for what to do with a "yes": stop, get the card, and add the coverage before the patient is roomed.
What the eligibility response already tells you
Most 271 eligibility responses include other-payer information when the payer knows about it. Medicare's eligibility response reports MSP records, including the other insurer and the effective dates. Commercial responses often list a primary plan when the plan considers itself secondary. Front-desk staff who only look for "active" miss this. Train them to look for the other-payer segment and to compare it with what the patient said; when the two disagree, that is the moment to sort it out, not after the denial.
Run eligibility two business days before the visit, not the morning of, so that a disagreement between the response and the record can be resolved by a phone call before the patient arrives. A response that shows an MSP record with an end date in the past is fine. One that shows an open record for an employer the patient says they left is the case to work.
Fixing the records when they are wrong
Sometimes the patient is right and the payer's file is wrong: the employer coverage ended two years ago and Medicare still shows it as primary. The practice cannot change Medicare's MSP record; the patient or the former employer must contact the Benefits Coordination and Recovery Center to update it. Give the patient the reason and the contact route, note the call in the account, and hold the claim rather than resubmitting into the same denial. Commercial plans usually accept a coordination of benefits update from the patient by phone or through the member portal, and many will not process claims at all until the member responds to a COB questionnaire they mailed months earlier. Ask the patient whether they received one.
A worked example
A cardiology practice pulled a year of CO-22 denials: 388 claims, $142,000 billed, 74 days average delay to final payment. Two hundred and ten were Medicare patients with active employer coverage that had never been recorded. Ninety were dependents billed to the wrong parent's plan. The rest were a mix of accident-related visits and Medicaid patients with other coverage. The practice added the four questions to check-in, trained the front desk to read the other-payer segment on eligibility responses, and set a rule that any patient over 65 with a commercial card on file is asked about current employment. Six months later, CO-22 denials were down to a handful a month, and the ones that remained were mostly payer file errors the practice could document on the day of the visit.
The dollar cost is worth putting in front of the owner. At 74 days of delay on $142,000, and with a share of the claims reaching the correct primary after its timely filing limit, the practice lost cash flow on every one of the 388 claims and lost some of the claims outright. Two minutes at check-in is cheap against that.
Questions we hear
Can we just bill Medicare and let the denial tell us?
You can, and it costs about two months per claim and a share of the claims to timely filing at the real primary. Payers also notice. Asking is cheaper.
The patient says they have no other insurance but Medicare denies CO-22 anyway. Now what?
Medicare's file has a record the patient does not know about or has forgotten, usually old employer coverage. The patient contacts the Benefits Coordination and Recovery Center to have it closed; the practice documents the date and holds the claim. It usually resolves in two to four weeks, and the claim is then resubmitted.
Who owns this?
The front-desk lead owns the questions and the eligibility review; the billing lead owns the CO-22 report and feeds the patterns back to the front desk monthly. When the two sit in the same meeting, the denials fall. Practices that want help closing the loop between registration and denials can look at how our denial management work reports root causes by front-desk step, or at our training courses for front-office and billing staff.
What to do this week
- Pull the last twelve months of CO-22 denials with the payer, the patient's age and the days to final payment, and sort them into the causes above.
- Add the four questions to the check-in script or intake screen, with a field for the date they were asked.
- Show the front desk where the other-payer segment appears in your eligibility tool, using three real responses from this week.
- Flag every patient over 65 who has a commercial plan on file and confirm current employment at their next visit.
- Set a monthly fifteen-minute meeting between the front-desk lead and the billing lead with the CO-22 report on the table.
