PR-50 vs CO-50: What the Group Code on Your EOB Means for Your Wallet

The two-letter prefix on a denial code on your Explanation of Benefits (EOB) determines who pays — not the number. PR-50 means you may be responsible for the bill. CO-50 means the provider writes it off. Both codes say the service was not medically necessary, but the group code — the letters before the hyphen — is the most financially significant detail on the entire document.

If you have private (commercial) insurance and saw an in-network provider, a CO-50 denial generally means you owe nothing for that line item. A PR-50 denial means the provider may bill you. This guide explains the difference and what to do next.

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What Are Group Codes?

Every Claim Adjustment Reason Code (CARC) on your EOB is paired with a group code — two letters before the number. The group code tells you who is financially responsible:

| Group Code | Stands For | Who Bears the Cost | |---|---|---| | CO | Contractual Obligation | The provider writes it off (contractual adjustment) | | PR | Patient Responsibility | You may owe the amount | | CR | Correction and Reversal | Prior adjustment being reversed | | OA | Other Adjustment | Third-party or other adjustments |

The number after the group code (e.g., 50, 4, 96) tells you why the adjustment was made. The group code tells you who pays.

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CO-50: Contractual Obligation — Not Medically Necessary

When you see CO-50 on your EOB:

• Meaning: The insurer determined the service was not medically necessary
• Financial impact (in-network): The provider must write off the denied amount under their participation agreement
• Can you be billed? Generally no, if you saw an in-network provider. Balance billing for a CO adjustment is a contract violation

For a full breakdown, see the detailed CO-50 denial code guide.

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PR-50: Patient Responsibility — Not Medically Necessary

When you see PR-50 on your EOB:

• Meaning: The insurer determined the service was not medically necessary
• Financial impact: You may be responsible for the charged amount
• Can you be billed? Yes — the provider may pursue collection for this amount

PR-50 is less common with private insurance than with Medicare. Under Medicare, PR-50 typically appears only when the provider obtained a signed Advance Beneficiary Notice (ABN) before the service. For private insurance, there is no standardized equivalent of the ABN, but some plans have voluntary waiver forms.

If you see PR-50 on your EOB:

1. Call the provider's billing office to confirm the code is correct
2. Ask whether an ABN or similar waiver was signed
3. If no waiver exists, ask the provider to appeal or correct the claim
4. File an internal appeal with your insurer if you believe the service was medically necessary

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Side-by-Side Comparison

| Detail | CO-50 | PR-50 | |---|---|---| | Group code meaning | Contractual Obligation | Patient Responsibility | | Denial reason | Not medically necessary | Not medically necessary | | In-network liability | Provider writes off | You may owe | | Out-of-network liability | Depends on state law | You may owe | | Medicare ABN required? | No ABN → CO-50 | Signed ABN → PR-50 | | Appeal possible? | Yes | Yes |

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How the Same Code Gets Different Group Codes

The same service denied for the same reason can show up as CO-50 or PR-50 depending on:

1. Provider network status — In-network denials are almost always CO; out-of-network may be PR
2. Signed waiver forms — Medicare ABNs shift CO-50 to PR-50
3. State law — Some states require specific group code usage
4. Plan type — ERISA vs. state-regulated plans handle group codes differently

Your EOB is the authoritative document for your specific situation. Always read the full code — both letters and number — before deciding your next step.

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What to Do Regardless of the Code

Whether you see CO-50 or PR-50, you have the right to appeal:

1. Read the RARC — The Remittance Advice Remark Code paired with the denial tells you the specific reason
2. Contact your provider — Ask about the diagnosis code submitted and whether it supports medical necessity
3. Get a Letter of Medical Necessity — Ask your doctor to explain why the service was necessary
4. File an internal appeal — You typically have at least 180 days from the denial notice under federal law (29 CFR §2560.503-1)

For practical steps, see the How to Read an EOB guide.

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How Hedical Can Help

Upload your EOB or denial letter to the Medical Bill & Denial Navigator. Our AI will decode every CARC, RARC, and group code, explain your financial exposure, and draft an appeal letter tailored to your denial reason.

Try the Bill & Denial Navigator — free for basic analysis.

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Sources

• ANSI X12 Claim Adjustment Reason Codes, Washington Publishing Company
• CMS Medicare Claims Processing Manual, Chapter 22
• 29 CFR §2560.503-1 — ERISA claims procedure
• 45 CFR §147.136 — External review standards
• Patient Advocate Foundation, "Letter of Medical Necessity Guide"