What a CO-45 denial means

What CO-45 means

CO-45 is the line on the remittance that brings your charge down to what the payer allows. The official X12 description of reason code 45 is "Charge exceeds fee schedule/maximum allowable or contracted/legislated fee arrangement." The payer still pays the line, on the allowed amount rather than on your charge.

For example, you charge $200 for a visit and the contract allows $120. The remittance shows CO-45 for $80. The $120 is then split between the payer’s payment and the patient’s share, which appears under group PR with reason codes such as 1 (deductible), 2 (coinsurance) or 3 (copay).

X12’s usage note sets two limits. The CO-45 amount can’t equal the whole charge, and code 45 goes with group CO or PR depending on who is liable for the difference.

Because the line was paid, CO-45 is usually not a denial at all, unlike CO-16 or CO-97. Our denial code reference covers the codes that are.

What CO means here: the write-off is yours

CO is the Contractual Obligation group. CMS’s remittance manual says CO adjustments come from a contract or a regulation and are generally a write-off for the provider, not billed to the patient. For a CO-45, that contract is your network agreement, or the fee schedule the payer is required to use.

Medicare spells it out. Under chapter 1 of the Claims Processing Manual, participating providers are paid from the physician fee schedule and must accept assignment: Medicare’s payment plus any unmet deductible and coinsurance is payment in full. Non-participating providers are paid 95 percent of the fee schedule amount.

Sending the CO-45 amount to the patient is balance billing. On a Medicare assigned claim it breaks the assignment agreement; for other payers, check the hold-harmless terms in your contract. If it happens, reverse the balance and refund what was collected.

Medicare: a reopening, not an appeal, for a wrong rate

If Medicare applied the wrong fee schedule amount, that is a clerical error under chapter 34 of the Claims Processing Manual, which lists misapplication of a fee schedule next to data entry and computer errors. Clerical errors go through a reopening, not an appeal. You can request one for any reason within one year of the initial determination, and Part B contractors must offer telephone reopenings.

Check the rate before you call. CMS’s Physician Fee Schedule Look-up Tool shows the payment amount for each code by MAC and locality, and the site-of-service rules decide whether the facility or nonfacility rate applies. If you disagree with the determination itself, not a calculation, ask for a redetermination within 120 days of receiving it.

If your charge was below the fee schedule, there is nothing to reopen. Under 42 CFR 414.21, Medicare pays on the lesser of the actual charge or the fee schedule amount.

How to prevent CO-45 problems upstream

You can’t prevent CO-45 itself; it is how contracted payment works. You can prevent the underpayments hiding behind it:

• Load every payer contract and fee schedule into your system, with effective dates, as soon as it is signed or renewed
• Set charges at or above the highest rate any payer allows for each code, and review them every year
• Confirm each new provider’s effective date and contract link before their claims go out, through credentialing and enrollment
• Check place of service codes against where the visit actually happened
• Have payment posting compare every allowed amount with the expected rate, not only post the deposit

When we run your billing, short payments behind CO-45 are worked the same way as denials: listed by payer, disputed with the contract page, and tracked to payment.