Who has to pay after a code 66 denial?

Usually your cost to pay. The letters in front of the number matter: CO (contractual obligation) usually means an in-network provider must absorb it, while PR (patient responsibility) means the plan says you owe it.

How long do I have to appeal?

It depends on your coverage: 180 days for most employer and marketplace plans, 120 days for Original Medicare, about 90 days for Medicaid (varies by state), and only 65 days for Medicare Advantage. Set your deadline clock before you do anything else.

All denial codes · code 66

Denial code 66: what it means — and how to fight it

Denial code 66 (shown on your EOB as CO-66 or PR-66) means: “Blood Deductible.” In plain English: Medicare makes you cover the first three pints of blood each year. This is a real cost you owe, not a denial of care.

low appealability Usually your cost to pay

What they're really saying

“Blood Deductible.”

Medicare makes you cover the first three pints of blood each year. This is a real cost you owe, not a denial of care.

Your odds

Check the math first — this is usually cost-sharing, not a judgment.

Not an appealable denial — but the charge disappears if the blood was replaced.

Fewer than 1 in 100 denied claims are ever appealed. When people do appeal, roughly 4 in 10 win the first round — and independent external review overturns 40–50% of what reaches it.

How to appeal a code 66 denial

Decode. You just did — this page is step one.
Set your clock. 180 days for most employer and marketplace plans, 120 for Original Medicare, ~90 for Medicaid, only 65 for Medicare Advantage.
Urgent? If this is care you still need, call and request an expedited appeal — they must decide within 72 hours.
Ask the hospital if the blood was replaced by a donor — that erases the charge. The deductible goes away if you or a donor replaces the blood, so ask the hospital whether blood was donated on your behalf and have them rebill. Confirm the three-pint count restarts each calendar year and that the hospital did not apply it twice in the same year. A Medigap policy or a secondary plan will often pay this amount.
Send it certified. Letter plus evidence, keep copies of everything.
Escalate. Denied again? Independent external review — a doctor who doesn't work for your insurer decides.

Do it in minutes, free

The AppealClock tool translates your denial, drafts your appeal letter, computes your exact deadline — and watches the clock so you don't have to. No account. Your medical details never leave your device.

Start your appeal & set your clock →

Common questions

What does denial code 66 mean?: Medicare makes you cover the first three pints of blood each year. This is a real cost you owe, not a denial of care.
Can I appeal a CO-66 or PR-66 denial?: Yes. Appealing is free and it is your legal right. For this code the odds are low: Not an appealable denial — but the charge disappears if the blood was replaced. Fewer than 1 in 100 denials are ever appealed — insurers count on silence.
Who has to pay after a code 66 denial?: Usually your cost to pay. The letters in front of the number matter: CO (contractual obligation) usually means an in-network provider must absorb it, while PR (patient responsibility) means the plan says you owe it.
How long do I have to appeal?: It depends on your coverage: 180 days for most employer and marketplace plans, 120 days for Original Medicare, about 90 days for Medicaid (varies by state), and only 65 days for Medicare Advantage. Set your deadline clock before you do anything else.