= payments ÷ (charges − contractual adjustments) × 100
One technology company (a “WISeR participant”) reviews requests in each state, using AI tools plus clinicians. A licensed clinician must review every non-affirmation.Because payments trail charges, build in a lag. For example, compare charges for January through June with payments posted through September, or use a trailing 12 months. Keep the window the same every time.
Unlike the
Meaning
Orthopedic example
Timely-filing and credentialing write-offs.
How to improve it
Unrelated procedure59 or XS used for procedures in the same joint or contiguous structures.The supplier bills before receiving a standard written order, or bills bilateral braces without separate RT and LT lines. See our review of
Why it matters in orthopedics
Orthopedic ICD-10-CM codes carry anatomic site and laterality. M17.11 is primary osteoarthritis of the right knee and M17.12 the left, so a single digit decides whether the diagnosis supports the procedure. A claim can be clinically correct and still fail when the diagnosis pointer links the wrong code to a line or the side doesn’t match. These denials are usually avoidable with pre-submission checks, which is why they appear in our guide to common orthopedic claim denials.
How it works
Payers use CARC 11 when the diagnosis and the procedure don’t match (X12 wording last modified July 1, 2017). If the payer fills in the 835’s healthcare policy identification segment, it names the policy behind the edit.
Related codes tell a different story. CARC 146 means the diagnosis wasn’t valid for the date of service, and CARC 167 means the diagnosis isn’t covered.
Medicare contractors may report a diagnosis that isn’t on a local coverage determination’s covered list as CO-50 with remark code N115 instead of CO-11. Noridian’s JF Part B denial list files that pairing under “medical necessity/no payable diagnosis.”
Remark codes you may see with diagnosis problems include M76 (the diagnosis is missing or invalid), M81 (the diagnosis needs more specificity), N115 (decision based on an LCD) and N386 (decision based on an NCD).
Group code CO assigns the amount to the provider. Medicare lets providers bill beneficiaries only for adjustments under group code PR.
Orthopedic example
A 58-year-old patient with right-knee osteoarthritis (M17.11) receives an injection in the right knee (20610 with modifier RT, a major-joint injection without ultrasound guidance). The claim lists M17.12, left-knee osteoarthritis, copied forward from an earlier visit. The diagnosis now contradicts the procedure side, and the payer can return the line as CO-11. The fix is a corrected diagnosis code, not an appeal.
Common denial triggers
Laterality conflicts among the diagnosis, the procedure and the RT or LT modifier.
Diagnosis pointers that link a line to the wrong diagnosis on a multi-line claim.
A symptom code, such as M25.561 (pain in right knee), when the payer’s policy requires the definitive diagnosis documented in the note.
Unspecified codes when the record supports a more specific one.
Diagnosis codes that weren’t valid on the date of service.
How to prevent or fix
Code to full specificity and confirm that side and site match across diagnosis, procedure and modifiers before submission.
Check diagnosis pointers on every line of multi-procedure claims, especially when one visit covers more than one joint.
For a processed Medicare claim, CMS treats transposed diagnosis codes and inaccurate data entry as clerical errors, so request a reopening. For other payers, send a corrected claim under their rules.
If the remark code says the diagnosis is missing or invalid (M76), treat it like a CO-16 data fix.
Appeal when the diagnosis was right and the payer’s edit is wrong. Send the visit note, imaging report and the payer policy that shows the diagnosis supports the service.
Frequently asked questions
How is CO-11 different from CO-50?
CO-11 says the diagnosis and procedure don’t fit together, which usually points to a coding or claim-building error you can correct. CO-50 says the payer judged the service not medically necessary, a coverage decision that often needs records and an appeal. Medicare contractors may report a diagnosis missing from an LCD’s covered list as CO-50 with remark code N115, so read the remark code before choosing a fix.
Can you fix a CO-11 denial without an appeal?
Usually, when the error was yours. For a processed Medicare claim, CMS classifies transposed diagnosis codes and inaccurate data entry as clerical errors that are corrected through a reopening rather than an appeal. Other payers accept corrected claims under their own rules and deadlines. If the diagnosis was correct and the payer’s edit misread it, appeal with the documentation and the payer’s policy instead.
Does a CO-11 denial let you bill the patient?
No. Group code CO assigns the balance to the provider, and Medicare lets providers bill beneficiaries only for amounts assigned to group code PR. A diagnosis and procedure mismatch is a claim problem to correct, not a patient balance. For commercial plans, check your participation agreement and state law, but treat a CO adjustment as the practice’s responsibility.
Guides that cover this term
Related terms
Sources
Claim Adjustment Reason Codes — X12, accessed October 14, 2026
Remittance Advice Remark Codes — X12, accessed October 14, 2026
Remittance Advice Resources and FAQs (ICN 905367) — CMS Medicare Learning Network, accessed October 14, 2026
Denial Code Resolution, JF Part B — Noridian Healthcare Solutions, last updated July 9, 2025
Medicare Claims Processing Manual, Chapter 34 (section 10.4, clerical error reopenings) — CMS, section effective September 30, 2016
This entry is educational and is not legal, coding-compliance or billing advice. Payer rules change often, so confirm requirements with the payer before you bill. CPT® is a registered trademark of the American Medical Association; code descriptions here are Rette’s plain-language summaries.