OA-23 shows how your primary insurance's payment affected your secondary claim. It isn't always a true denial — but the math behind it is wrong more often than most patients realize.
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The plain English translation — and why it's not automatically a denial.
OA-23 almost always appears on a claim processed by your secondary (or tertiary) insurance. It's an accounting entry showing that the amount being adjusted reflects what your primary insurance already paid or adjusted — not a fresh judgment about whether the service itself is covered.
The "OA" (Other Adjustment) group code is used here specifically because coordination of benefits (COB) doesn't cleanly fit "provider's fault" (CO) or "patient's fault" (PR) — it's a math problem between two insurers. Your secondary plan is supposed to pay some portion of what's left after the primary insurer's payment, based on its own allowed amount and your remaining cost-sharing.
The issue: this calculation is done incorrectly far more often than people expect — especially when the secondary payer doesn't receive complete information from the primary payer, or when the two insurers disagree about which one should be primary in the first place.
A coordination-of-benefits calculation has several places it can go wrong.
Secondary insurance is generally supposed to pay the lesser of its own allowed amount minus what the primary already paid, or your remaining patient responsibility — not zero out the claim automatically. If the secondary payer's math doesn't add up against both EOBs side by side, this is a straightforward correction request, not a real coverage dispute.
Coordination-of-benefits order follows specific rules — employer plan vs. spouse's plan, the "birthday rule" for dependent children, or Medicare Secondary Payer regulations. If the payer order was determined incorrectly, the entire OA-23 calculation is built on the wrong foundation and needs to be redone from scratch with the correct primary/secondary designation.
Sometimes the secondary insurer processes the claim before receiving complete information about what the primary insurer actually paid or adjusted, leading to an inaccurate or automatic zero-payment result. Submitting the primary payer's EOB directly to the secondary insurer often triggers a full reprocessing of the claim.
Four steps that consistently correct coordination-of-benefits errors.
Request the primary insurer's Explanation of Benefits showing exactly what it paid and adjusted, and the secondary insurer's EOB showing what it applied against your claim. You cannot verify a COB calculation without both documents in front of you.
Confirm which plan should actually be primary based on applicable COB rules — your employer plan, a spouse's plan, the birthday rule, or Medicare Secondary Payer regulations. If the order is wrong, this is your strongest and most fundamental correction point.
Compare the secondary plan's allowed amount minus what the primary already paid against what was actually applied to your claim. If the numbers don't match, document the exact discrepancy — this becomes the core of your dispute.
Submit both EOBs along with a written explanation of the discrepancy to the secondary insurer, and copy the primary insurer if the payer order is in question. Insurers are required to reprocess claims when a documented coordination-of-benefits error is identified.
Because OA-23 reflects a calculation rather than a coverage decision, cases where both EOBs clearly show a math discrepancy resolve at high rates. Cases involving a disputed payer order require more documentation but often carry the largest financial impact.
Upload both your primary and secondary EOBs. ClaimCompass checks the coordination-of-benefits calculation, verifies the payer order, and generates the dispute letter you need if something's off.
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