PR-66 means the payer applied the blood deductible, and the patient owes that amount. It shows up most on Medicare claims where a patient got whole blood or packed red cells. Under Medicare, the patient pays for the first three units of blood in a calendar year unless the blood is replaced by a donor. Most PR-66 lines are correct. The ones worth checking are those where blood was replaced, units were counted twice, or the hospital didn’t actually pay for the blood. (Primary sources: X12 Claim Adjustment Reason Codes · Medicare.gov, blood).
In brief: PR-66 means “Blood Deductible.” The patient owes it. Under Medicare, the deductible covers the first three units of blood a year, shared across Part A and Part B. Check the units on the claim, any units replaced by donors, and units already counted earlier in the year. Then bill the patient or their supplemental plan for the correct amount.
Part of our denial codes library. Written by Manikandan J, CPC, CRCR, who has billed hospital and lab claims for payers and billing companies. Published 20 October 2026. Last updated: 20 October 2026. Code wording is quoted word for word from X12.
Official CARC 66 wording
| Field | Official X12 text |
|---|---|
| Description | “Blood Deductible.” |
| Start | 01/01/1995 |
Source: X12 Claim Adjustment Reason Codes, checked 20 October 2026.
Denial code 66, CARC 66 and reason code 66
Denial code 66, CARC 66 and reason code 66 all mean the blood deductible. The PR group is the normal one, because the deductible is the patient’s share by design. If you see CO-66, ask the payer why, since a contractual group would stop you from billing the patient.
How the Medicare blood deductible works
A blood deductible is the patient’s share for the first units of blood they get each year. A unit is one pint of whole blood or one unit of packed red cells. Replaced blood is blood that a donor gives to the blood bank on the patient’s behalf to make up for what the patient used.
| Rule | What it means |
|---|---|
| First three units each calendar year | The patient pays for these or replaces them |
| Shared across Part A and Part B | Units counted under one part count toward the other |
| Replacement | Each unit replaced by a donor removes one unit from the deductible |
| Free blood | If the hospital got the blood at no cost, there’s usually nothing to pay or replace |
Medicare.gov explains that in most cases hospitals get blood from blood banks at no charge. When the hospital has to buy blood, the patient either pays for the first three units or has the blood donated. Processing and handling of blood are a different charge.
Where blood shows on the claim
On the UB-04 (837I), hospitals report blood with revenue codes in the 038X range and blood processing with 039X. Value codes carry the unit counts:
| Value code | Meaning |
|---|---|
| 37 | Units of blood furnished |
| 38 | Units of blood in the deductible (not replaced) |
| 39 | Units of blood replaced |
If value code 38 is wrong, PR-66 will be wrong too. For example, a claim with 3 units furnished, 1 replaced and a value code 38 of 3 will overstate the patient’s share by one unit.
When PR-66 needs a second look
- Units were replaced. A family member donated, but value code 39 was left blank.
- The deductible was already met. The patient had blood earlier in the year at another hospital.
- Free blood. The hospital got the blood at no cost, so there’s no deductible to apply.
- Counted twice. The same units appear on an inpatient claim and an outpatient claim.
- Wrong year. A stay that crossed 1 January split units into the wrong calendar year.
How to work a PR-66 line
- Count the units on the claim and match them to the transfusion record.
- Subtract replaced units using the blood bank’s donor credit.
- Check the year to date for blood already counted under Part A or Part B.
- Fix the value codes and send a corrected claim if 38 or 39 was wrong.
- Bill the secondary plan, such as a Medigap policy, if it covers the blood deductible.
- Bill the patient for any amount left.
Worked example (illustrative)
A Medicare patient gets 4 units of packed red cells during a hospital stay in March. Her son donates 2 units at the hospital’s blood bank. The first claim shows value code 37 = 4 and value code 38 = 3, with nothing in 39. The remit shows CAS*PR*66 for three units. The biller checks the donor record, finds the two replaced units, and sends a corrected claim with value code 38 = 1 and value code 39 = 2. The payer reprocesses, and the patient owes for one unit instead of three. Her Medigap plan then covers that one unit.
Prevention checklist
- [ ] Link blood bank donor credits to the patient’s account before billing.
- [ ] Check value codes 37, 38 and 39 on every claim with blood revenue codes.
- [ ] Ask about blood received earlier in the year at other facilities.
- [ ] Don’t apply a deductible when the blood was free to the hospital.
- [ ] Bill Medigap or Medicaid before sending a patient statement.
Related denial codes
- PR-1, PR-2, PR-3: deductible, coinsurance and copay.
- CO-1: deductible amount under the CO group.
- OA-23: impact of prior payer adjudication.
- PR-204: service not covered under the patient’s benefit plan.
- CO-16: claim lacks information needed for adjudication.
- Denial codes hub for every code we cover.
Key takeaways
PR-66 is the patient’s blood deductible. Under Medicare, it covers the first three units of blood each year, shared across Part A and Part B, and each donor-replaced unit lowers it. Check the units, replacements and year to date, fix value codes 38 and 39 when needed, and bill the secondary plan before the patient.
FAQ
What does PR-66 mean?
It means the payer applied the blood deductible, and the patient is responsible for that amount.
How many units are in the Medicare blood deductible?
The first three units of whole blood or packed red cells in a calendar year.
Does donated blood reduce PR-66?
Yes. Each unit replaced by a donor takes one unit off the deductible.
Which value codes report blood units?
Value code 37 is units furnished, 38 is units in the deductible, and 39 is units replaced.
Does Medigap cover the blood deductible?
Many Medigap plans do. Check the patient’s plan before billing them.
Is the blood deductible part of the Part A deductible?
No. It’s a separate deductible for blood, shared across Part A and Part B.
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 66). Accessed 20 Oct 2026.
- Medicare.gov, Blood. Accessed 20 Oct 2026.
- CMS, Medicare General Information, Eligibility and Entitlement Manual, Ch. 3, Deductibles, Coinsurance Amounts, and Payment Limitations. Accessed 20 Oct 2026.
Last updated: 20 October 2026 · This page is educational and doesn’t replace payer contracts or coding rules.