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CO-288 Denial Code: Referral Absent

CO-288 means the patient's plan requires a referral, usually from the primary care provider, for this service, and the payer had no referral on file for the date of service. Under CO the provider absorbs the denial unless a valid referral is found or obtained and the claim is reprocessed.

Quick facts

Code
CO-288 (CARC 288)
Status
Active In use since November 1, 2017.
Code set
Claim Adjustment Reason Codes (CARC)
Group codes
  • CO (Contractual Obligation): The usual group. The provider is responsible for the missing referral and can't bill the patient on this denial.
  • PR (Patient Responsibility): Some plans hold the member responsible for self-referring. The patient may be billed only if the plan reports PR and any required notice was given.
Official description
Referral absent
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What CO-288 means

CARC 288 says referral absent. The patient’s plan requires a referral before this service is covered, and the payer had no referral on file that matched the patient, the rendering or billing provider, and the date of service. This is most common in HMO, managed Medicaid, and point-of-service plans that use a primary care gatekeeper model.

The denial is about paperwork, not the medical need for the visit. If a referral existed and simply wasn’t linked, or if the plan accepts retroactive referrals, the claim can often be recovered. If no referral was ever issued and the plan won’t accept one after the fact, the loss usually stays with the provider under the CO group code.

Older remittances used CARC 165, “referral absent or exceeded,” which was deactivated in 2018. Its two situations now have separate codes: CARC 288 for a missing referral and CARC 287 for a referral that was exceeded.

Common causes

  • No referral requested. Front desk didn’t recognize the plan as referral-based.
  • Referral issued to a different provider or group NPI than the one that rendered or billed the service.
  • Referral expired or its start date fell after the date of service.
  • Referral entered by the PCP but not yet in the payer’s system when the claim adjudicated.
  • Referring provider missing from boxes 17 and 17b on plans that match referrals from the claim.
  • Patient changed PCPs, and the referral came from a provider no longer assigned.

How to fix it

  1. Check the payer portal for any referral on file for the patient, and compare its provider, dates, and visit count to the claim.
  2. If a valid referral exists, ask the payer to reprocess, or send a corrected claim with the referring provider in 17/17b and resubmission code 7 in box 22.
  3. If none exists, contact the patient’s PCP and ask whether the plan allows a retroactive referral. If it does, have it entered and request reprocessing.
  4. Appeal when the plan’s referral rules didn’t apply, such as emergency care, direct-access services like certain OB/GYN or behavioral health visits, or plan types that don’t require referrals.
  5. Write off or bill according to the group code once options are exhausted.

How to prevent it

  • Flag referral-based plans in your practice management system during eligibility checks.
  • Verify the referral before the visit, including provider, date range, and number of visits.
  • Track remaining visits on multi-visit referrals so you know when a new one is needed.
  • Keep referring provider data on every claim. A Claims Validator check can catch a blank box 17b before submission.

For a broader look at authorization and referral failures, see authorization and referral denials.

Specialty notes

Specialists, PT/OT practices, and behavioral health groups that take managed Medicaid or HMO plans see CO-288 most. Some plans exempt certain specialties from referral rules, so keep a payer-by-payer list rather than assuming.

Remark codes that may appear with CO-288

  • N489 (Missing referral form.): The referral form itself is missing.
  • N475 (Missing completed referral form.): The completed referral form is missing, which some payers need on paper or in their portal.
  • N335 (Missing/incomplete/invalid referral date.): The referral date is missing or invalid, for example a referral dated after the visit.
  • CO-287 (Referral exceeded): A referral existed but the services went beyond it, such as more visits than referred.
  • CO-197 (Precertification/authorization/notification/pre-treatment absent.): Precertification or authorization absent, a utilization management requirement rather than a PCP referral.
  • CO-243 (Services not authorized by network/primary care providers.): Services not authorized by the network or primary care provider.
  • CO-242 (Services not provided by network/primary care providers.): Services not provided by network or primary care providers.

Related articles

CO-288 FAQ

What is the difference between a referral and a prior authorization?

A referral is usually the primary care provider's approval for the patient to see a specialist, common in HMO and some point-of-service plans. Prior authorization is the payer's own approval of a specific service. A plan can require one, both, or neither.

Can a referral be obtained after the visit?

Some plans accept retroactive referrals within a short window, others don't. Ask the PCP's office to enter it and ask the payer whether it will reprocess the claim.

Where do I put the referral on the claim?

The referring provider's name and NPI go in boxes 17 and 17b. Some payers also want a referral number in box 23. Many plans check their own referral database rather than the claim.

Can I bill the patient for CO-288?

Not under the CO group code. If the plan reports PR, for example because the member self-referred, you may bill the patient according to your agreements.