Quick Explanation
Denial code CO-105 indicates that a portion of the claim payment has been withheld for federal or state tax purposes, typically due to backup withholding. This occurs when there is a discrepancy between the provider's Taxpayer Identification Number (TIN) and the legal business name on file with the payer or the IRS. This is a financial adjustment rather than a denial of medical necessity, meaning the payer is legally mandated to withhold these funds until tax documentation is corrected.
Common Causes for CO-105
Denials with code CO-105 typically happen for the following specific reasons:
- The provider's Taxpayer Identification Number (TIN) or Employer Identification Number (EIN) does not match official IRS records.
- The provider failed to submit a completed and signed IRS Form W-9 to the payer during the credentialing or onboarding process.
- The IRS has issued a B-Notice (backup withholding directive) to the insurance payer due to consecutive years of mismatched TIN/name combinations.
- An administrative or clerical error was made in Box 25 of the CMS-1500 claim form or the electronic 837P equivalent, transmitting an incorrect tax ID.
How to Prevent CO-105 Denials
To avoid receiving this denial in the future, implement these specific checks:
- Verify the provider's TIN, EIN, and legal business name against official IRS documentation, such as the CP 575 or 147C letter, before submitting claims.
- Proactively submit an updated and signed IRS Form W-9 to all contracted payers annually and immediately following any corporate restructures or name changes.
- Perform routine audits of billing software configurations to ensure the tax identification information transmitted in the loop 2010AA (837 electronic files) is accurate.
- Promptly respond to any payer notifications or IRS inquiries regarding tax ID mismatches to resolve discrepancy flags before backup withholding is implemented.
Appeal Letter Template for CO-105
If you believe this claim was denied incorrectly, you can use the following template to submit an appeal.
[Your Practice Header]
[Date]
[Payer Name]
[Appeals Department Address]
RE: Appeal for Claim [Claim Number]
Patient: [Patient Name]
ID: [Patient ID]
Date of Service: [Date]
Denial Code: CO-105 - Tax withholding
Dear Appeals Department,
I am writing to appeal the denial of the above-referenced claim, which was denied with code CO-105: "Tax withholding".
We are writing to request the immediate release of the funds withheld under adjustment code CO-105 (Tax Withholding) for the enclosed claims. In accordance with IRS Section 3406 guidelines governing backup withholding and CMS Medicare Claims Processing Manual guidelines, we have enclosed a certified, signed copy of our current IRS Form W-9 alongside our official IRS letter (CP 575/147C) confirming our correct legal entity name and Taxpayer Identification Number (TIN). The tax information associated with this provider is accurate and fully verified. Please update your provider demographic records immediately to reflect these verified tax details, cease any active withholding, and reprocess the affected transactions to issue the outstanding payments due to our practice.
Attached please find:
1. A copy of the original claim.
2. The relevant medical records supporting the service.
3. [Any other supporting documents].
We respectfully request that you reprocess this claim for payment.
Sincerely,
[Your Name]
[Title]
[Practice Name]
Stop Writing Appeals Manually
Clausea can read your medical records and generate custom, evidence-based appeals for denial code CO-105 in seconds.
Generate Appeal for CO-105 Now