CO · Contractual ObligationCARC 288

Denial Code CO-288

Q: What does CO-288 mean?

CO-288 is a Contractual Obligation (CO) denial: "Referral absent." The service required a referral that wasn't on file, so the payer denied it. It's the referral counterpart to a missing authorization — the gatekeeping step the plan requires wasn't completed or recorded.

Q: Is CO-288 the patient's responsibility or a provider write-off?

CO-288 carries the CO group code (Contractual Obligation): Provider/contractual responsibility — not billable to the patient while denied. A CO adjustment is the provider's responsibility, not the patient's: balance-billing the patient for a CO amount is a contract (and often compliance) violation. But CO does not automatically mean “write it off.” When the cause is fixable — missing information (CO-16), a modifier problem (CO-4), or NCCI bundling (CO-97) — you correct and resubmit, or appeal with documentation. You only truly write the amount off when it is a final contractual adjustment, such as the fee-schedule difference on CO-45.

Referral absent.

Source: X12 Claim Adjustment Reason Codes (CARC) & Group Codes. Maintained by the D3rx Clinical Billing Team.

What CO-288 means

The service required a referral that wasn't on file, so the payer denied it. It's the referral counterpart to a missing authorization — the gatekeeping step the plan requires wasn't completed or recorded.

Why CO-288 happens

A required referral from the primary-care provider was never obtained
A referral exists but wasn't submitted to or recorded by the plan
The referral expired before the date of service
The service performed fell outside what the referral covered

What to do when you get CO-288

1Check whether a valid referral actually exists; if so, submit/reference it and resubmit
2If no referral was obtained, request a retroactive referral from the PCP where the plan allows
3Confirm the referral covers the rendered service, provider, and date
4Document medical necessity to support a retro-referral or appeal

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CO group code: who absorbs the charge

Contractual Obligation — Provider/contractual responsibility — not billable to the patient while denied.

A CO adjustment is the provider's responsibility, not the patient's: balance-billing the patient for a CO amount is a contract (and often compliance) violation. But CO does not automatically mean “write it off.” When the cause is fixable — missing information (CO-16), a modifier problem (CO-4), or NCCI bundling (CO-97) — you correct and resubmit, or appeal with documentation. You only truly write the amount off when it is a final contractual adjustment, such as the fee-schedule difference on CO-45.

Appeal, correct, or write off CO-288?

If a referral existed and was simply not on the claim/plan record, that's a correction — submit it and resubmit. If no referral was obtained, appeal or request a retroactive referral with the PCP's support, especially for urgent/emergent care where many plans waive the requirement. Under the CO group code you cannot bill the patient without valid advance notice.

Timing & deadlines

Act quickly — retro-referral and appeal windows are short and payer-specific. Standard anchors apply (Medicare redetermination 120 days from the remittance; commercial ~180 days), but retro-referral requests often cap at a few business days after the service or denial.

Example

A specialist visit on a gatekeeper plan is billed without a referral on file and returns CO-288 (referral absent). If the PCP intended to refer, obtaining a retroactive referral and resubmitting can recover payment.

Prevent CO-288 going forward

Verify a valid referral is on file before scheduling gatekeeper-plan services
Confirm the referral covers the exact provider, service, and date span
Track referral expiration dates so they don't lapse before the visit
Build a referral check into specialty scheduling workflows

Code families most affected

Specialist services on gatekeeper/HMO plans
Referral-gated diagnostics and procedures
Coordinated-care plan services

Related codes

Denial codes you'll often see alongside CO-288

CO-197 CO-95

Payer notes

CO-288 ('referral absent') is the referral analog of CO-197 (authorization absent). The same CARC appears as PR-288 when the plan shifts the balance to the patient (e.g., the patient bypassed the referral process knowingly).

Turn this CO-288 denial into a sent appeal

D3rx drafts a ready-to-send, e-signable appeal letter for CO-288 from your claim details — free, backed by CMS, Medicare, and major-payer data.

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Medical billing disclaimer

CARC/RARC definitions are the standardized X12 set; group-code semantics follow the X12 Claim Adjustment Group Code standard. Filing and appeal windows vary by payer — the standard anchors shown (Medicare redetermination 120 days from the remittance; Medicare timely filing 12 months from date of service; most commercial payers ~90-180 days) are general references, not a guarantee for any specific plan. Always confirm the rule in the payer's provider manual before acting. D3rx is not responsible for claim outcomes.