CO 45 denial code

What CO-45 means

CO-45 appears on a remittance advice when your billed charge is higher than the amount the payer allows for that service: the fee schedule amount for Medicare, or the contracted rate for a commercial plan. The payer pays its allowed amount (less patient cost sharing) and tags the difference with CO-45.

The group code matters. CO stands for contractual obligation: the adjustment is the provider’s write-off under its agreement with the payer, and the patient cannot be billed for it. For a participating Medicare provider, accepting assignment means accepting the fee schedule amount as payment in full.

In dollar terms: you bill $150 for an office visit, the payer allows $92.14. The remit shows the payment plus patient responsibility adding up to $92.14, and a CO-45 adjustment of $57.86. That $57.86 comes off your accounts receivable as a contractual write-off.

CO-45 is one of the highest-volume codes on any remit, and most occurrences are routine. It becomes a problem in two situations: the allowed amount is lower than your contract says it should be, or your chargemaster is set so close to (or below) allowed amounts that you cannot see underpayments at all.

Common causes

• Standard pricing. Billed charges are almost always set above allowed amounts, so nearly every paid line carries some CO-45. This is expected.
• Underpayment. The payer loaded the wrong fee schedule, applied an old contract year, or priced the service under a different provider agreement than yours.
• Wrong payer or plan. The claim adjudicated under a plan with a lower fee schedule than the one the patient actually holds.
• Charge entry errors. A billed amount keyed with an extra digit inflates the CO-45 figure and can distort your write-off reporting.

How to fix and resubmit

1. Compare the allowed amount on the remit to your contracted rate for that code, place of service, and date of service. For Medicare, check the current fee schedule amount; the RVU calculator gives you the Medicare allowed amount by locality.
2. If the allowed amount matches your contract, post the CO-45 as a contractual write-off and move on. There is nothing to fix, and for Medicare there are generally no appeal rights on this adjustment.
3. If the payer allowed less than your contracted rate, do not resubmit the claim: resubmitting a paid claim usually triggers a duplicate denial (CO-18). Instead, request a reprocessing or file a payment dispute with the payer, citing the contract rate, the code, and the date of service.
4. If the underpayment is systematic (every claim for a code family pays short), escalate to your provider relations representative with a spreadsheet of affected claims rather than disputing one at a time.

How to prevent it

You cannot prevent routine CO-45 adjustments, and you should not try to by lowering charges: billing below the allowed amount means the payer pays the lower of the two, and you leave money on the table permanently.

What you can do is make underpayments visible. Load payer fee schedules into your billing system so posted allowed amounts are checked against expected amounts automatically. Review CO-45 write-off percentages by payer monthly; a payer whose write-off ratio suddenly rises is often paying from the wrong fee schedule. And keep charge amounts uniform across payers: charge variation makes CO-45 analysis useless. For a full list of adjustment codes, see the denial codes index.