Medicare Paid, Secondary Didn’t: Check the Crossover
By George Ruan • October 7, 2026
Last reviewed: October 7, 2026.
When Original Medicare pays but no secondary payment shows up, first check the Medicare remittance for a crossover indicator, then ask the secondary payer whether it received and paid the claim. In our experience, the secondary has often already paid and the payment simply never reached your billing system. Do not refile the claim or bill the client for the remainder until you know which it is.
Sections
Read the Medicare remittance first
The CMS COBA companion guide identifies remark codes MA18 and N89 as signs that Medicare selected the claim for crossover. They mean the claim was forwarded, not that the secondary accepted or paid it. Medicare also explains that most Medigap plans receive Part B claim information directly. Medicare Advantage plans work differently, so this checklist covers Original Medicare only.
The usual reasons the secondary looks unpaid
It paid, but there is no ERA. If the practice never enrolled in electronic remittances with the supplement, its payment can arrive as a paper check or EOB, or not appear in the EHR at all. A payer status check may say “paid” while your system shows nothing.
The supplement lapsed. We have seen a client’s Medicare supplement suspended without the client knowing. The only fix is for the client to sort out the coverage.
The leftover balance is not the supplement’s to pay. After Medicare, part of what looks like an open insurance balance is often Medicare’s contractual adjustment, not coinsurance. A supplement pays Medicare’s cost sharing, not amounts Medicare adjusted off.
The secondary claim has not gone out yet. When crossover does not happen, someone has to file the secondary claim once the primary posts.
How to check with the secondary payer
Confirm the secondary coverage was active on the date of service and that the member details match the payer’s records.
Run an electronic claim status check if you can. A “paid” response often lacks the amount, payee, and payment date. A “not found” response is inconclusive; it does not prove the claim never crossed over.
If status alone does not answer it, call the payer. Ask for the paid amount, payment date, check or EFT number, and where the payment was sent. Keep Medicare’s claim number separate from the secondary’s own claim number.
Only if the payer confirms it never received the claim, follow its direct-submission instructions with the Medicare remittance attached. Search for an existing secondary claim first so you do not send a duplicate.
Before you bill the client
Compare both remittances line by line. Bill the client only for what is actually their responsibility after both payers. When a client is checking on their supplement, we pause automatic charges for those visits rather than collect and refund later.
Billing protections apply separately. CMS prohibits billing Qualified Medicare Beneficiaries for Medicare Part A or Part B cost sharing on covered services, even when Medicaid pays nothing. A zero balance in the EHR for a QMB client still leaves the secondary claim to work.
Bomi traces secondary payments through claim status and payer calls before anything is refiled or billed. For background on Medicare participation status, see participating vs non-participating vs not enrolled.
Frequently Asked Questions
Does MA18 on the Medicare EOB mean the secondary paid?
No. It means Medicare forwarded the claim. Confirm receipt and payment with the secondary payer.
The supplement says the claim is paid, but I never got anything. What now?
Ask the payer for the payment date, amount, payee, and check or EFT number. In our experience, a paper check or a missing ERA enrollment with that payer is the usual explanation.
Should I just resubmit the secondary claim?
Not until the payer confirms it has no record of the claim. Resubmitting a claim that was already paid creates duplicates without getting you paid faster.
Can I bill a QMB client if Medicaid pays nothing?
No. QMB clients cannot be billed for Medicare cost sharing on covered services, whatever Medicaid pays.
Sources
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