Denial codes on your EOB, explained

Your explanation of benefits (EOB) is your insurer's record of a claim. Next to the numbers, you may see short codes like CO-45, PR-1, or CO-16. These codes explain why your plan paid less than the provider billed, and who is responsible for the rest.

This page explains each part of a code and what the most common ones mean. For each code, it tells you what to do next. It's part of our guide on how to appeal an insurance denial.

Where do these codes come from?

When your plan processes a claim, it sends the provider an electronic payment notice. That notice uses standard codes from national lists. A national standards group called X12 publishes these lists. The reason code list is updated 3 times a year.

There are 3 kinds of codes:

• Group codes are 2 letters, like CO or PR. They show who is responsible for an amount.
• Claim adjustment reason codes (CARCs) are numbers, like 45 or 197. They give the main reason for the change.
• Remittance advice remark codes (RARCs) start with M, MA, or N, like N130. They add detail.

Your EOB may combine the first 2 into one code, like CO-45. The letters are the group code, and the number is the reason.

For most private plans, a denial notice must include the denial code and what it means. You can also ask your plan for the diagnosis and treatment codes on a denied claim. Asking for them doesn't count as filing an appeal.

What do CO, PR, OA, and PI mean?

The 2 letters tell you whose responsibility an amount is. This is often the most useful part of the code.

The key question is simple: is the amount marked PR? Only PR amounts are ones your plan says the provider may bill you. If a provider bills you for an amount marked CO, ask the billing office why.

Common claim denial codes and what to do

This table lists the claim adjustment reason codes people see most often on EOBs and denial letters. The meanings are plain-language versions of the official X12 descriptions. Look for the number after the letters.

If you see code 22 and you have 2 plans, the plans may disagree about who pays first. Our guide to coordination of benefits explains how that order works.

Code 242 often shows up on bills from anesthesiologists, radiologists, and other doctors you didn't choose. See out-of-network anesthesia at an in-network hospital and does the No Surprises Act apply to my bill.

What do remark codes like N130 mean?

A remark code adds detail to a reason code. Codes 16 and 96 are always supposed to come with a remark code. Here are a few you may see.

Remark codes that start with "Alert" share information only. They don't explain a change in payment. CMS keeps the remark code list, but any health plan can use it.

Say Priya's EOB from an in-network clinic shows 3 lines. Here's what it says.

Service	Amount billed	Plan paid	You may owe	Codes
Office visit	$250	$120	$30	CO-45 $100, PR-3 $30
Lab test	$180	$0	$0	CO-16 $180, remark M51
Acupuncture	$120	$0	$120	PR-204 $120
Total	$550	$120	$150

Here's how she reads each line.

• Office visit. CO-45 is the $100 network discount, so she doesn't owe it. PR-3 is her $30 copay. $250 − $100 − $30 = $120, which matches what her plan paid.
• Lab test. CO-16 with M51 means a procedure code was missing or wrong. She owes $0 for now. She asks the clinic to fix the code and send the claim again.
• Acupuncture. PR-204 means her plan doesn't cover it. She checks her plan documents, and they exclude acupuncture. She may owe the $120.

So Priya pays $30 for the visit now. She waits for the corrected lab claim before she pays anything for it.

What to do when you see a denial code

1. Find the group code. If it's CO, the amount is generally not yours to pay. If it's PR, you may owe it.
2. Look up the reason. Use the table above, or the explanation printed on your EOB.
3. Decide who fixes it. Paperwork codes, like 4, 16, 31, and 109, usually need the provider to send a corrected claim. Coverage codes, like 50, 96, 197, and 204, usually need an appeal.
4. Call before you pay. Ask the billing office to hold your account while you sort it out.
5. Appeal if you disagree. For most private plans, you have 180 days from the denial notice to file an internal appeal. Our insurance appeal letter gives you the words.

Our guide to what to do when insurance didn't pay a medical bill walks through each fix. If your bill asks for more than your EOB says you owe, compare them with our guide to an EOB vs. a medical bill.

When to get help

You can often figure out a code with 1 call to your insurer. It's worth getting help when:

• Your EOB shows a code with no explanation, and member services can't explain it.
• The provider and your insurer each say the other one needs to act.
• A denied claim is large, or it's already in collections.
• You're handling claims for someone else and you're short on time.

Your insurer's member services number is on your insurance card. Your denial letter should list your state's consumer assistance office, if it has one. For employer plans, the Department of Labor's Employee Benefits Security Administration answers questions at 1-866-444-3272.

For surprise out-of-network bills, call the No Surprises Help Desk at 1-800-985-3059. A medical bill advocate can also make the calls for you.