Skip to main content
Call
CARC 66 · CO-66

CARC 66 Denial: Blood Deductible — How to Fix and Appeal

Reviewed by QuickIntell RCM Editorial Team · Last reviewed

Updated

TL;DR

CARC 66 (X12 Blood Deductible). CARC 66 applies the Medicare blood deductible (first three pints per year are patient responsibility).

Official X12 description

“Blood Deductible.”

Source: X12 Claim Adjustment Reason Codes. The X12 External Code Lists are the single authoritative source for every CARC descriptor — always verify against the current release before building a claim-scrub rule.

What CARC 66 actually means

CARC 66 applies the Medicare blood deductible (first three pints per year are patient responsibility). Shift the amount to patient responsibility.

Common root causes

  • Medicare blood deductible applied for the first three pints of blood per year.

Prevention checklist

  • Blood-deductible tracking at inventory/administration for Medicare patients.

Appeal strategy — step by step

Most CARC 66 denials clear faster with the right remediation than with a formal appeal. Work the steps in order and escalate only when a lower-effort path has been ruled out.

  1. 1Not appealable — Medicare benefit design.
Sample appeal-letter language for CARC 66
[Provider letterhead] Re: Appeal of CARC 66 — Claim #{claim_number} Member: {member_name} · Member ID: {member_id} Date(s) of Service: {dos} On {remittance_date} this claim was adjusted with CARC 66: "Blood Deductible." We respectfully request reconsideration. The X12 External Code List definition of CARC 66 does not apply to this claim for the following reasons: 1. [Cite the clinical / coding / policy fact that rebuts the adjustment] 2. [Cite the supporting documentation attached — op note, EOB, LCD/NCD citation, NCCI edit indicator, modifier rationale] 3. [Cite the payer's own policy where applicable] Attached: {list supporting documents} Please process payment under the member's benefits. If additional information is required, contact the billing office at {provider_phone} or {provider_email}. Sincerely, {billing_manager_name}, {credentials}

Edit the bracketed fields before sending. This template is a starting point; a payer-specific appeal form may still be required — check the provider portal first.

Payer-specific notes

Payer-specific behavior for CARC 66 publishes here as the QuickIntell anonymized denial ETL ingests sufficient volume. In the meantime, consult the payer directory for the relevant provider manual and appeal form.

How common is CARC 66?

Search demand rank
#117

Out of 306 seeded CARCs, ranked by combined US monthly search volume for "CARC 66", "CO-66 denial", and "denial code 66".

Platform frequency
Pending ETL

Platform frequency ranks publish once the anonymized denial-rate pipeline reaches the publication threshold (strategy §12 Phase 2).

How QuickRCM prevents CARC 66

QuickRCM catches the root causes above before the 837 leaves the clearinghouse:

  • Claim-scrub rules fire on every root cause listed above — the scrub references the same X12 CAS segment logic that drives the denial, so what the payer checks, QuickRCM checks first.
  • When a denial lands, QuickRCM routes it to the correct worker with the documentation bundle already attached (op note, LCD citation, modifier rationale, EOB, primary 835).
  • Appeal templates tuned to each CARC (including this one) pull the supporting facts from the claim and fill the bracketed fields automatically.
See QuickRCM →Book a demo

Frequently asked questions — CARC 66

What does CARC 66 mean?

CARC 66 is an X12 Claim Adjustment Reason Code. The official definition is: "Blood Deductible." In plain English, the payer is telling you cARC 66 applies the Medicare blood deductible (first three pints per year are patient responsibility). Shift the amount to patient responsibility.

How do I resolve a CARC 66 (CO-66) denial?

Start with the most common root cause: Medicare blood deductible applied for the first three pints of blood per year. First step: Not appealable — Medicare benefit design. See the full remediation and appeal checklist on this page before filing a formal appeal.

Is CARC 66 patient responsibility?

No — CARC 66 is typically carried under CO (Contractual Obligation) or OA (Other Adjustment), which means it is the provider's responsibility, not the patient's. Do not bill the patient unless the 835 CAS group code is PR.

What does CARC 66 look like on an EOB or 835 remittance?

On the 835 ERA, CARC 66 appears in Loop 2110 CAS segment as "CAS*CO*66*{amount}". On a paper EOB the same code prints in the Adjustment/Denial Reason column with the X12 description: "Blood Deductible." — usually paired with one or more RARC remark codes in the same remittance line for additional context.

Can CARC 66 be appealed successfully?

Yes — when the root cause does not apply to the specific claim. Overturn rates are strongest when the appeal cites the X12 definition, the payer's own published policy, and documentation that rebuts the payer's rationale. The sample appeal language block above is a starting point; always adapt it to the payer's reconsideration form.

Disclaimer

This page is operational reference for medical-billing professionals. It is not legal, clinical, or contractual advice. X12 code descriptors are maintained by the X12 External Code Lists; always verify against the current X12 release and the payer's own published policy before submitting or appealing a claim.