CO-61 means the payer cut or denied the surgery claim because the plan required a second surgical opinion and none was on file. This rule is rare today, but some employer plans, union plans and state Medicaid programs still have it for certain planned surgeries. Most CO-61 denials are fixed in one of three ways. You show the second opinion was done, you show the surgery was exempt, or you show the plan didn’t require one. (Primary sources: X12 Claim Adjustment Reason Codes · Medicare.gov, second surgical opinions).
In brief: CO-61 means “Adjusted for failure to obtain second surgical opinion.” Read the plan’s rule to see which surgeries need a second opinion and who may give it. Check whether a second opinion was done but not sent, and whether the case was an emergency. If the rule didn’t apply or was met, appeal with proof. If it applied and wasn’t met, the cut usually stands under CO.
Part of our denial codes library. Written by Manikandan J, CPC, CRCR, who has worked surgical claim denials for payers and billing companies. Published 20 October 2026. Last updated: 20 October 2026. Code wording is quoted word for word from X12.
X12 text for CARC 61
| Field | Official X12 text |
|---|---|
| Description | “Adjusted for failure to obtain second surgical opinion” |
| Start | 01/01/1995 |
| Last modified | 03/01/2017 |
Source: X12 Claim Adjustment Reason Codes, checked 20 October 2026.
Notice the word “adjusted”. Many plans don’t deny the whole claim. They pay less, as a penalty for skipping the second opinion.
Denial code 61, CARC 61 and reason code 61
Denial code 61, CARC 61 and reason code 61 are the same thing. Under CO, the provider’s contract keeps the cut amount with the provider. Some plans put the penalty on the member instead and send PR-61. Read the group code before you send a bill.
What a second surgical opinion program is
A second surgical opinion program is a plan rule that says a member must see a second surgeon before certain planned surgeries. The second surgeon reviews the case and says whether they agree surgery is needed. An elective surgery is a planned operation that isn’t an emergency, such as a knee replacement. Plans that use these programs usually list the surgeries that need one.
| Often on second-opinion lists | Usually exempt |
|---|---|
| Hysterectomy | Emergency surgery |
| Spinal fusion or back surgery | Surgery during an inpatient stay for trauma |
| Knee or hip replacement | Cancer surgery when delay is unsafe |
| Weight-loss (bariatric) surgery | Cases where the plan waived it in writing |
| Tonsil removal in adults | Surgery the plan pre-approved |
Each plan writes its own list. Treat the table as a guide to what to look for, not as the rule.
Medicare and second opinions
Original Medicare doesn’t require a second opinion. It does pay for one. Medicare.gov says Part B covers a second opinion for surgery that isn’t an emergency, and a third opinion if the first two disagree. So CO-61 on an Original Medicare claim is unusual. If you see it from a Medicare Advantage plan, ask for the plan rule in writing.
Why CO-61 happens
- The opinion was done but not sent. The second surgeon’s note never reached the payer.
- The wrong doctor gave it. For example, the second surgeon was in the same group as the first.
- The timing was off. The plan wants the opinion before surgery, and it was done after.
- No one checked the rule. Pre-surgery checks covered prior authorization but not the second-opinion rule.
- An emergency wasn’t flagged. The claim didn’t show the case was urgent.
How to work a CO-61 line
- Read the plan rule. Find the list of surgeries, who may give the opinion, and the timing.
- Look for an opinion on file. Check the chart and the referral notes.
- Check exemptions, such as emergency status, inpatient trauma, or a written waiver.
- Send the proof. Attach the second surgeon’s note and the dates.
- Appeal if the rule didn’t apply or was met.
- Post the cut under CO when the rule applied and wasn’t met, and fix your pre-surgery checklist.
Worked example (illustrative)
A union health plan requires a second opinion before spinal fusion. A surgeon does a fusion, and the claim comes back with CAS*CO*61*1800.00, a penalty cut from the payment. The coordinator finds that the patient did see a second surgeon two weeks before surgery. That note sat in the referral system and was never sent. She sends it with a short letter that cites the plan rule. The payer reprocesses and pays the full amount.
Consider a different case. A patient has an urgent appendix removal on a plan with a second-opinion rule. The claim gets CO-61 because the emergency room note wasn’t attached. The biller appeals with the note, since emergency surgery is exempt under the plan.
Prevention checklist
- [ ] Add a second-opinion check to your pre-surgery steps, next to prior authorization.
- [ ] Keep a list of plans that require second opinions and the surgeries they cover.
- [ ] Make sure the second surgeon is outside the first surgeon’s group if the plan asks.
- [ ] Send the second-opinion note with the auth request or the claim.
- [ ] Mark emergency cases clearly on the claim.
Related denial codes
- CO-197: precertification or authorization absent.
- CO-50: not deemed a medical necessity.
- CO-252: attachment or other documentation required.
- CO-226: requested information not provided.
- CO-16: claim lacks information needed for adjudication.
- Denial codes hub for every code we cover.
Key takeaways
CO-61 is a penalty for skipping a plan’s required second surgical opinion. Read the plan rule, look for an opinion already done, and check emergency exemptions. Appeal with proof when the rule was met or didn’t apply. When it applied and wasn’t met, post the cut and add a second-opinion step to your pre-surgery checks.
FAQ
What does CO-61 mean?
It means the payer reduced or denied the claim because a required second surgical opinion wasn’t obtained.
Does Medicare require a second surgical opinion?
No. Original Medicare doesn’t require one, but Part B covers a second opinion for non-emergency surgery.
Can I bill the patient for CO-61?
Not under the CO group. Some plans put the penalty on the member and send PR-61 instead.
Is emergency surgery exempt?
In most plans, yes. Send the emergency room or admission note with your appeal.
Who can give the second opinion?
The plan decides. Many require a surgeon who isn’t in the same group as the first surgeon.
How do I appeal a CO-61?
Send the second surgeon’s note and dates, or show the surgery was exempt or not on the plan’s list.
Sources
How we checked: every code quote on this page was compared word for word with the X12 CARC list on 20 October 2026.
- X12, Claim Adjustment Reason Codes (CARC 61). Accessed 20 Oct 2026.
- Medicare.gov, Second surgical opinions. Accessed 20 Oct 2026.
- CMS, Medicare Benefit Policy Manual, Ch. 15, Covered Medical and Other Health Services. Accessed 20 Oct 2026.
Last updated: 20 October 2026 · This page is educational and doesn’t replace payer contracts or coding rules.