Appeal or corrected claim?

Corrected claim if the claim was actually wrong — it is faster and it is what the payer expects. This appeal is for when the claim was correct as submitted and the payer's edit misfired, which is a different argument entirely.

Why insist on reprocessing rather than resubmission?

Because a claim treated as new gets a new received date, and on an older claim that can push you past the timely filing limit — turning a fixable denial into an unfixable one.

CO-16

Appeal letter template: claim lacks information (CO-16)

For CO-16 denials where the claim was correct as submitted. Includes the timely-filing protection that matters most on these.

Free, no signup required to read or copy it. Replace every bracketed field before sending, and refer to the patient by initials and account reference only — never a full name.

Use this when

The remittance shows CO-16 with remark codes you have reviewed.
The information the payer says is missing was in fact submitted.
The field flagged is not required for this service under the payer's own guide.
You are asking for reprocessing rather than submitting a corrected claim.

The letter

[PRACTICE NAME]
[PRACTICE ADDRESS]
[PHONE] · [FAX]

[DATE]

[PAYER NAME] — Appeals Department
[APPEALS ADDRESS FROM YOUR REMITTANCE]

RE: Appeal of claim denial
Claim number: [CLAIM NUMBER]
Patient reference: [PATIENT INITIALS] / [ACCOUNT REFERENCE]
Date of service: [DATE OF SERVICE]
Billed amount: [AMOUNT]
Denial code: CO-16 — claim/service lacks information or has submission/billing error(s)
Remark code(s): [RARC CODES FROM YOUR REMITTANCE]

To the Appeals Department:

We are appealing the denial of the claim identified above. The remittance indicates the claim lacked information, referencing remark code [RARC CODE].

[CHOOSE THE PARAGRAPH THAT MATCHES YOUR SITUATION AND DELETE THE OTHERS]

[IF THE INFORMATION WAS SUBMITTED] The information identified by the remark code was present on the claim as originally submitted on [SUBMISSION DATE]. A copy of the claim as submitted is attached, showing [DESCRIBE THE FIELD AND ITS CONTENT]. We ask that the claim be reprocessed as originally filed.

[IF THE INFORMATION IS NOW PROVIDED] The information identified by the remark code is provided with this appeal: [DESCRIBE WHAT IS ATTACHED]. As the original claim was submitted timely on [SUBMISSION DATE], we ask that it be reprocessed rather than treated as a new claim, so that the original filing date is preserved.

[IF THE FIELD IS NOT REQUIRED] The remark code refers to a data element that is not required for this service under the plan's published billing requirements. We ask that the edit be reviewed and the claim processed as submitted.

[IF ELIGIBILITY IS THE ISSUE] The member's coverage was active on the date of service. Eligibility verification obtained on [VERIFICATION DATE] is attached. We ask that the claim be reprocessed against the correct eligibility record.

Attached in support of this appeal:
[LIST ATTACHMENTS — remittance advice, claim as submitted, eligibility verification, requested documentation]

We ask that you reprocess this claim and remit payment in the amount of [AMOUNT].

Please provide a written determination within your stated appeal-response window. If any additional documentation would assist the review, contact me directly at [PHONE] or [EMAIL].

Sincerely,

[NAME]
[TITLE]
[PRACTICE NAME]
[NPI / TAX ID]

How to adapt it

Read the remark codes before writing anything. CO-16 is deliberately generic and the RARC carries the actual reason — without it you are guessing at what to argue.
The request to reprocess rather than treat as a new claim is the important sentence. It is what protects the original filing date.
If the claim genuinely had an error, a corrected claim is usually faster than this letter. Use this when the claim was right as submitted.

Understand the denial first

CO-16CO-16 denial: claim lacks informationSomething on the claim is missing or malformed. CO-16 almost never travels alone — a RARC alongside it tells you what.

Common questions

Appeal or corrected claim?: Corrected claim if the claim was actually wrong — it is faster and it is what the payer expects. This appeal is for when the claim was correct as submitted and the payer's edit misfired, which is a different argument entirely.
Why insist on reprocessing rather than resubmission?: Because a claim treated as new gets a new received date, and on an older claim that can push you past the timely filing limit — turning a fixable denial into an unfixable one.

Or skip the blanks entirely

Undeny reads the denial document, fills every one of these fields from it, and tracks the appeal deadline. About three minutes instead of thirty.

Generate your appeal letter See pricing