Denial codes · Denial code

CO-45 on a nutrition claim: usually not a denial, just your contract rate

By Javier Alvarez · Updated September 29, 2026 · 5 min read

If CO-45 is the only adjustment on your nutrition claim, relax: the claim was processed. CO-45 is how the payer tells you the difference between what you charged and what your contract (or its fee schedule) allows. It is the single most common adjustment on any remittance, and on a normal in-network 97803 line it is exactly what you expected to happen.

This page covers why it appears, how to post it, and the two situations where a CO-45 does deserve a second look.

What CO-45 means (official X12 wording)

The X12 Claim Adjustment Reason Code list defines CARC 45 as:

"Charge exceeds fee schedule/maximum allowable or contracted/legislated fee arrangement."

The usage note adds two rules worth knowing: the adjustment "cannot equal the total service or claim charge amount", and it is to be used "only with Group Codes PR or CO depending upon liability". In other words, CO-45 is never supposed to wipe out a whole line on its own, and the group code in front tells you who absorbs the difference.

• CO-45: contractual obligation. You agreed to the allowed amount, so the excess is your write-off. You cannot bill it to the patient.
• PR-45: patient responsibility. The payer is saying the patient owes the excess, which is typical of out-of-network claims where no contract limits your fee.

How CO-45 shows up on a normal MNT remit

Every line on an ERA balances: billed = paid + every adjustment. An invented example for a 45-minute follow-up billed as 97803 x 3 units:

Nothing on that line is a denial. You post $91.20 as the payer payment, $66.00 as a contractual adjustment and $22.80 as the patient's balance. If you use the ERA/EOB walkthrough, CO-45 is the first adjustment you learn to post automatically.

The numbers are illustrative. What payers actually allow for 97802 and 97803 varies by payer, contract and state; see dietitian reimbursement rates for how to find yours.

Why the write-off is large (and why that is fine)

Most practices set one fee schedule for everyone, at or above the highest rate any payer pays. That means every lower-paying contract generates a big CO-45. The size of the write-off tells you nothing about whether you were paid correctly. The allowed amount does.

Medicare MNT

Medicare works the same way. CMS's claims manual says registered dietitians and nutrition professionals "must accept assignment" for MNT, and that Medicare pays "the lesser of the actual charge, or 85% of the physician fee schedule amount" when an RD provides the service (Pub. 100-04, Ch. 4 §300.3–300.4). Anything you billed above that allowed amount comes back as CO-45, and assignment means you cannot collect it from the beneficiary. Deductible and coinsurance still apply and appear as PR-1 and PR-2.

When a CO-45 deserves a second look

1. The allowed amount is below your contract

This is an underpayment hiding behind a normal code. Common reasons on nutrition claims:

• The wrong fee schedule was loaded. New contracts, renewals and mid-year rate changes are often keyed late.
• Units were cut. If you billed four units of 97803 and the payer allowed three, the reduction may appear as CO-45 or as a separate code (often one about units or frequency). Compare allowed units with billed units.
• A different provider was paid. If the claim went out under a group NPI or taxonomy the payer maps to a lower rate, the allowed amount drops. Check the rendering NPI in Box 24J and the billing NPI in Box 33; our Type 1 vs Type 2 NPI guide explains the setup.
• A telehealth rate or modifier differential was applied that your contract does not include.

What to do: pull your contract's fee schedule for the date of service and compare line by line. If the payer applied the wrong rate, call provider services and ask for a reprocessing, or file a payment dispute or appeal with the fee schedule page attached. Some payers call this a "claim reconsideration" rather than an appeal; the provider manual gives the name and the deadline. Do not send a corrected claim for an underpayment: nothing on the claim was wrong.

2. CO-45 on a line that paid $0

A line where the allowed amount went entirely to the deductible (PR-1) is normal. A line where CO-45 plus another CO code equals the whole charge is a denial, and the other code is the real reason. Read it: CO-97, CO-16 or CO-50 are the usual partners on nutrition claims.

3. You are out of network and see CO-45

If you have no contract with the payer, a CO group code on the excess means the plan is applying some other agreement, often a rental network or a repricing vendor that claims you accepted its rates. Ask the payer which agreement it applied. If you never signed one, dispute it in writing.

How to post CO-45 correctly

1. Post the payment to the line.
2. Post CO-45 as a contractual adjustment, not as a bad debt or a denial. Keeping them separate is how you will later spot underpayments.
3. Move PR amounts to the patient (PR-1 deductible, PR-2 coinsurance, PR-3 copay). See PR-1, PR-2 and PR-3.
4. Record the allowed amount per code per payer. After a few remits you have your real fee schedule, which is what you need for collecting copays and estimates at the visit.

How to prevent CO-45 surprises

• Get every fee schedule in writing when you sign a contract, and ask for the rates for 97802, 97803 and 97804, plus G0270 if you see Medicare patients.
• Keep one charge per code for all payers and review it yearly so it stays at or above your best contracted rate.
• Check the first remit after any contract change. Rate updates are where keying errors happen.
• Watch the allowed amount, not the paid amount. Paid amounts swing with deductibles every January; allowed amounts should not.

For the full list of codes on a nutrition remit and what each one means, go back to the denial code lookup.