Can I bill the patient for a CO-45?

No. CO means contractual obligation, and on code 45 the contract is the whole point. You agreed to accept the payer's rate, and this line is the difference between your fee and that rate. Charging the patient for it is balance billing. The letters are the only thing that decides this, and code 45 does allow PR, so read your own line before you assume.

Is CO-45 even a denial?

Usually not. Most CO-45 lines sit next to a payment. The payer allowed the service, priced it at the contracted rate, and reported the gap between your charge and that rate as code 45. It shows up as a denial in some software because it reduces the line, but nothing was refused. If a claim paid nothing at all and the only code is 45, that is worth a call.

Which group codes are allowed with code 45?

Only CO and PR. The code list attaches a note to code 45 saying to use it only with group codes PR or CO depending on who is liable. That makes PI-45 and OA-45 outside the rule. Most codes carry no such limit, so this one is unusual and worth knowing.

Should I appeal a CO-45?

Not as an appeal. The useful move is to compare the payer's allowed amount against the fee schedule in your contract. If they match, there is nothing to argue and the write-off is correct. If they do not match, ask the payer to reprice the claim and quote your contracted rate. That is a repricing request, and it is faster and more likely to work than an appeal.

RemitBench/Denial codes/CO-45

CO-45 denial code

CO-45 is the gap between what you billed and what the payer allows. On most claims it is not a denial at all. It sits right next to a payment.

What it means: Your charge was higher than the payer's allowed amount. Code 45 is the difference. The service was covered and the claim usually paid.
Who owes the money: Practice write-off CO makes it yours. It is the discount your contract promised the payer. The code list allows only CO or PR here, so read your own line, but on a contracted claim CO is the right answer and the patient owes none of it.
Is appealing worth it: Almost never as an appeal. Do one check instead. Put the payer's allowed amount next to the fee schedule in your contract. If they match, the write-off is correct. If they do not, ask for a repricing.

A CO-45 is never a patient balance. This is the plainest write-off on the whole site. You signed a contract agreeing to accept the payer's rate, and this line is the part of your fee that the rate does not reach. Billing the patient for it is balance billing.

One number worth checking. Code 45 is not allowed to equal the whole charge on the line. That limit is written into the code itself. If a payer adjusted 100 percent of a line as 45, nothing was allowed, and a fee reduction is not what happened.

What the number on the line actually is

Most confusion about this code clears up as soon as you see the arithmetic. Here is one line of a paid claim.

Amount	What it is
210.00	Your charge. The number on your fee schedule.
138.40	The payer's allowed amount. The rate in your contract.
71.60	`CO-45`. The gap. Your write-off, and the reason the payer wanted a contract.
27.68	`PR-2` coinsurance. The patient's share of the allowed amount, not of your charge.
110.72	Paid to you.

Nothing was denied. The payer covered the service, priced it at the agreed rate, and reported the difference. That is what code 45 is for, and it is why it appears on so many lines: every contracted claim where your fee is above the rate produces one.

Why your software calls it a denial. Code 45 reduces the line, and a lot of billing software files every reduction under denials. That makes 45 look enormous in a denial report while nothing is actually wrong. Before you spend a week on your top denial code, check whether those claims paid.

The industry does not treat it as a denial either

Two pieces of evidence, and both are checkable.

The industry keeps a table of approved code combinations covering four denial situations: missing documentation, missing claim data, a service the plan does not cover, and a benefit that is not separately payable. Codes 96 and 97 are both in it. Code 45 appears in none of the four. The table simply does not govern it, because a pricing reduction on a paid line is not a denial.

One large Medicaid plan's published crosswalk makes the same point from the other direction. Code 45 is the most used code in the whole document, on over 150 of its internal codes, and nearly all of those rows are marked as paid rather than denied.

Remark codes you will see with it

Usually none, and that is normal. Unlike code 96, code 45 does not require a remark, and payer crosswalks bear that out. In one behavioral health plan's mapping, five of its seven code 45 rows carry no remark at all. In the Medicaid crosswalk above, 150 of the 152 rows carry none.

One dead code to watch for. Plenty of articles pair code 45 with remark N14, which describes payment based on a contracted or fee schedule amount. That remark was switched off on 1 October 2007, and its own retirement note tells you to consider reason code 45 instead. The arrow points the other way. If a page shows you 45 with N14 today, it is copying something written twenty years ago.

The version that should worry you

There is one CO-45 that is a real problem, and it is the silent one. If your charge is lower than the payer's allowed amount, there is no gap, so there is no code 45 on the line at all. The payer simply pays your charge and keeps the difference.

Nothing on the remittance tells you this happened. The only way to find it is to compare your fee schedule against the allowed amounts you are actually being paid, once a year. A missing 45 costs more than a large one.

Why the payer sent it

Nearly all of these are the system working correctly. A few are not.

Normal contracted pricing. Your fee is above the contracted rate, so the payer wrote the difference off. Nothing to do.
The wrong fee schedule was loaded. Payers keep several. A claim priced against last year's schedule, or against the wrong region, still comes back as a 45.
Your contract renewed and their system did not. New rates take effect on paper before they take effect in the claims system more often than anyone likes.
The place of service changed the price. The same procedure is often allowed at a different rate in a facility than in an office.
A modifier changed the price. Modifiers that split a service into parts, or mark an assistant, reduce the allowed amount by design.
You have no contract with that payer. Then the allowed amount comes from a law or a plan rule rather than an agreement, and who owes the gap is a different question.

Read the letters in front of the 45

This code is unusual. Most reason codes say nothing about which group codes may be used with them, so the payer picks. Code 45 does say. Its own text limits it to PR or CO, depending on who is liable. That is a real rule from the code list, not a convention.

CO-45: Contractual obligation. What you will see on almost every contracted claim. Your write-off, and never a statement line.
PR-45: Patient responsibility. The code allows it, and we could not find a single payer mapping that actually sends it. Treat a PR-45 as a question rather than an instruction, and check your contract and your state's balance billing rules before anything reaches a statement.
PI-45: Outside the rule. The code names only PR and CO. A PI-45 is worth a phone call.
OA-45: Outside the rule too. Same answer.

Compare that with code 96, which carries no such limit and arrives with all sorts of letters. The medical habit of reading the number and assuming the letters happens to be safe on a 45 more often than on other codes. It is still a habit worth breaking, because the exception here puts money on a patient.

There is one more piece of evidence for CO being the intended pairing, and it comes from a retired code. Code A2, "contractual adjustment", was switched off on 1 January 2008, and the code list's own note tells you to use code 45 with group code CO instead. That is the standard saying in plain words what a contractual adjustment looks like now.

The rule almost nobody reads

Code 45 carries a longer note than most codes, and both halves of it are useful.

It cannot be the whole charge

The note says this adjustment cannot equal the total charge for the service or the claim. The logic is simple. If the payer allowed nothing, then there is no allowed amount for your fee to exceed, and a fee reduction is not what happened. The honest code for that is one of the not-covered codes.

So a line where the billed amount and the 45 amount are the same number is a red flag. Ask the payer what was actually applied. It is usually a non-covered service reported under the wrong code, and the two need very different work.

It must not repeat what a previous payer already took

The other half of the note is about claims with more than one payer. It says the amount must not duplicate adjustments that came out of an earlier payer's decision.

That rule exists because of how a secondary payer reads your claim. Medicare's own secondary payer manual says the way to report a primary payer's allowed amount is to put the difference in the claim's adjustment segment as CO-45. The secondary then works backwards: the primary's allowed amount is your submitted charge minus the CO-45 amount.

So the 45 amount is not a note. It is arithmetic that another payer will rely on, and two things break it.

Stacking two payers' reductions. With two payers ahead of you, adding their 45 amounts together makes the allowed amount look far too low. Medicare's instruction is to use the largest single one, because those reductions are two views of the same charge rather than two separate cuts.
A 45 equal to the whole charge. Subtract it and the allowed amount is zero, so the secondary payer calculates that it owes nothing. That is the practical reason the code is not allowed to equal the full charge.

When a secondary claim will not balance, this is the first place to look. Send the primary's adjustments as the primary's adjustments, and let the secondary calculate its own.

What to do next

Check whether the claim paid

Look at the paid amount on the line, not at the code. This one step ends most CO-45 questions.
If it paid: the 45 is the contractual discount. Post it as an adjustment. There is nothing else to do unless step 2 turns something up. If it paid nothing and 45 is the only code: that breaks the code's own rule. Call the payer and ask what was applied.
Put the allowed amount next to your contract

This is the only check on the page that finds money. Take the allowed amount from the remittance and find the same procedure code in the fee schedule attached to your contract.
If they match: the write-off is right. Move on. If the allowed amount is lower: you were underpaid. Do not file an appeal. Ask the payer to reprice the claim, and quote your contracted rate and its effective date.
Look for a pattern before you work one claim

A pricing error is rarely on one claim. If a rate is loaded wrong, every claim with that procedure code since the rate changed is wrong the same way.
Pull the same code across a few months. One underpaid claim is a phone call. Two hundred is a project, and it is worth escalating to your provider representative with the list attached.
Watch the secondary claim

If another payer is next in line, send the primary's adjustments as they were reported. Do not merge them into your own numbers, and do not let a 45 travel forward as though the secondary made it.
Fix your own fee schedule once a year

Your charge should sit above the highest rate any of your payers allows. If it sits below, you are paid your charge and nobody tells you. That is the quiet leak this code hides.

45 against 96 and 97

These three are the reduction codes people mix up, and the difference is about whether money moved and where it went.

Code	What the payer is actually saying
45	Covered, and priced lower than you billed. Money was paid. The gap is your contractual discount.
96	Not covered at all, and a remark code has to say why. No allowed amount was set. See the CO-96 page.
97	Covered, and already paid inside another service on the claim. Money moved to a different line. See the CO-97 page.

Short version: with a 45 you were paid less. With a 97 you were paid elsewhere. With a 96 you were not paid.

Other codes that get mixed up with 45

Code	How it differs from 45
42	The code that used to do this job. It was switched off on 1 June 2007 and the code list tells you to use 45 instead. If you find 42 in an old reference, it is dead.
59	A reduction from multiple or concurrent procedure rules, such as a second surgery in the same session. A pricing rule rather than a fee schedule cap. Many payers report it here instead of under 45.
131	A discount negotiated for that specific claim, rather than a standing contracted rate. Common on out-of-network claims a third party repriced.
209	An amount cut by a law or agreement that you may not collect from the patient, though you may bill it to the next payer. Its own text limits it to group code OA.
151	Too many units or too many visits, rather than too high a price. The payer is arguing about quantity.
119	The benefit maximum for the period is used up. Not a pricing question at all. See the CO-119 page.
18	An exact duplicate. Nothing was repriced, because the line was already handled. See the CO-18 page.

When not to appeal

The allowed amount matches your contracted rate. That is the deal you signed. There is nothing to argue.
The claim paid and you have not checked the fee schedule yet. Do the check first. It decides whether there is anything here at all.
Your charge is simply higher than every payer's rate. That is normal and it is how a fee schedule should be set.
The real problem is a rate loaded wrong. That is a repricing request, not an appeal, and it moves faster.

There is one version worth pushing on. When the payer's allowed amount does not match the fee schedule attached to your signed contract, you are not appealing a decision. You are pointing at an agreement. Bring the rate, the effective date, and a list of the affected claims.

Does 45 show up in dental?

Far less than you would expect, and the reason matters if you post dental remittances.

One large dental carrier publishes a document mapping its own processing policies to the standard codes. It runs to more than 900 policy rows across 354 pages. Not one of them uses code 45. The words "maximum allowable" and "fee arrangement" do not appear in it either. The only 45 anywhere in the document is a remark code, N45, which is a different thing.

That carrier reduces fees constantly. It just reports those reductions under other codes: 96 on over four hundred policies, 50 on more than a hundred, 16, 119 and 97 after that.

And the letters are not CO

Where a medical payer would send CO, that carrier sends PI or PR, and which one you get often depends on whether the dentist is in network. That is the same pattern the CO-96 and CO-97 pages describe, and it is the single biggest difference between posting medical and posting dental.

So the medical instinct fails twice here. A dental fee reduction usually is not coded 45, and when you do find one, CO is not the safe assumption it is on a medical remittance. Read the letters on the line in front of you.

Where a dental office does meet a 45

On the medical side. When a dental office bills oral surgery, sleep appliances or anesthesia to a medical carrier, that claim is priced by medical rules, and medical rules report contracted pricing under this code. If you send claims to medical carriers, everything above applies to you.

Related codes

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