Coordination of Benefits Errors: The Denial Cause Most Practices Overlook

Coordination of benefits denials are the category billing teams recognize by code, CO-22, but rarely address systematically at intake. Most practices treat them as one-off problems to fix after the fact rather than a pattern to prevent upstream. The result is a steady trickle of recoverable revenue that gets written off or shifted to patients. For background on why verification matters in the first place, see our guide on why verifying insurance is critical for healthcare providers.

Your Practice Is Writing Off COB Denials That Would Get Paid If You Reworked Them

Roughly 70 percent of COB denials get paid when corrected and resubmitted. But as many as 65 percent of denials overall are never reworked. For small practices without dedicated denial staff, COB denials are especially likely to fall into this gap because the rework involves multiple payers, updated COB records and resubmission in a specific order. The combination of complexity and understaffing means these denials get written off or billed to the patient. AHIMA notes that as many as 60 percent of returned claims are never resubmitted, and COB sits squarely in the high-effort, high-recovery slice of that bucket.

Three Scenarios Where COB Problems Hide Until After the Claim Denies

The same handful of patient situations account for most COB denials. If your billing team can recite these from memory, intake can flag them in advance.

Medicare plus employer or retiree coverage. The primary/secondary relationship flips when a patient turns 65 or retires. The front desk has the Medicare card on file as primary, but the employer plan is still active and should be billed first. The claim goes to Medicare, denies for COB, and the employer plan’s timely filing window may already be closing by the time the rework starts.

Dual commercial plans from two working spouses. Both plans are active but the birthday rule or subscriber relationship determines which is primary. The front desk picks one, bills it, and the claim denies because the payer’s records show a different primary. The denial reads CO-22 and the rework requires a payer call to confirm which plan the payer actually has on file as primary.

COBRA, marketplace or Medicaid as secondary. A patient switches jobs and picks up COBRA or a marketplace plan but still has Medicaid as secondary. The front desk assumes the new plan is the only plan. The claim denies because the payer’s COB records show a different hierarchy, and Medicaid as payer of last resort triggers further coordination requirements before anything gets paid.

Your Eligibility Check Probably Missed the Patient’s Other Insurance

Standard payer portals surface primary coverage reliably but there is no evidence they consistently expose all secondary or tertiary coverage. CMS Medicaid guidance warns that electronic eligibility sources vary in accuracy and timeliness. Experian’s 2025 State of Claims data show that incomplete registration and eligibility data remain top denial drivers despite widespread use of electronic tools. Portals commonly miss COB status and true primary payer identity, and whether the patient has additional active coverage through a spouse, parent, COBRA or retiree plan. The gap between what portals show and what a payer call reveals is where most COB denials originate. Fuse closes that gap by combining portal lookups with direct payer calls, so COB status and secondary coverage surface before the claim goes out, not after the denial comes back.

Five Intake Questions That Catch COB Problems Before the Visit

A short scripted set of questions during scheduling or check-in catches most COB scenarios before they become denials.

1. Do you have any other active health insurance besides this plan? Catches dual commercial, spousal and parent plans that patients often forget to mention.

2. Are you covered under a spouse’s or parent’s employer plan? Catches birthday rule scenarios and dependent coverage where the patient is not the subscriber.

3. Have you changed jobs, retired or lost coverage since your last visit? Catches COBRA pickups, retiree plan transitions and Medicaid added as secondary.

4. Do you have Medicare, Medicaid or any government coverage in addition to this plan? Catches Medicare as secondary for working aged patients and Medicaid wraparound situations.

5. Has anything changed about your insurance since we last saw you? A catch-all for plan changes patients don’t think to mention until the EOB shows up.

How to Rework a COB Denial Before It Becomes a Permanent Write-Off

When a CO-22 denial lands, the order of operations determines whether the claim gets paid or written off.

1. Contact the payer and update COB information. Clarify which plan is primary based on birthday rule, employment status or Medicare coordination rules. Confirm what each payer has on file, not just what the patient says.

2. Submit the claim to the correct primary payer within its timely filing window. Most commercial plans use 90 to 180 day windows; Medicare allows 12 months from the date of service. The clock that matters is the true primary’s, which may have started running well before the original denial.

3. Once the primary payer processes the claim, submit to the secondary with the primary EOB attached. Secondary payers will not adjudicate without the primary’s payment information, and missing EOBs trigger another round of denials.

Common mistakes that turn fixable COB denials into permanent write-offs:

• Appealing the denial with the secondary payer instead of first billing the true primary.

• Treating COB denials as patient responsibility and billing the balance to the patient.

• Failing to update COB in the payer’s system, causing repeated denials on every future claim for the same patient.

COB denials reward practices that catch them early at intake and treat them as a category, not a stack of individual problems. The patient’s coverage situation is almost always knowable before the visit. The work is making sure intake actually surfaces it. When Fuse runs verification, COB status and secondary coverage are part of the structured benefits result that writes back into the EMR, so the billing team starts each claim with the right primary on file.