CO-38 denial code
Services not provided or authorized by designated network or primary care providers
How to fix it
Obtain a retroactive referral where the plan permits it, or appeal with evidence the referral requirement was met.
How to prevent it
Confirm at scheduling whether the plan is gatekeeper-based and whether a current referral is on file.
In practice
A patient with an HMO plan self-refers to a specialist. The visit happens, the specialist bills, and the claim returns CO-38 because the plan required the primary care physician to authorise the referral first.
Gatekeeper plans make the referral a condition of payment rather than an administrative nicety. Without it the service is treated as though it were never authorised, regardless of how appropriate the care was or how clearly the patient needed it.
Many plans permit a retroactive referral within a defined window, often thirty to sixty days, if the primary care physician is willing to issue one. That is the fastest route. Where the window has closed, the appeal has to argue urgency or that a referral genuinely existed and was not transmitted.
What sits behind it
The reason this denial lands on the specialist rather than the primary care physician is worth understanding, because it feels unfair and shapes how practices respond. The plan pays the rendering provider, so the rendering provider carries the loss, even though the referral was somebody else's to issue.
That asymmetry makes verification at scheduling the only real defence. Confirming referral presence when the appointment is booked costs a few minutes; discovering its absence after the encounter costs the entire visit, and patients rarely accept a bill for a service they believed was covered.
Related codes divide the same territory more finely. CO-288 states the referral was simply absent, CO-287 that its visit limit was exceeded, and CO-243 that a network gatekeeper declined to authorise. Reading which one arrived narrows what to ask for when calling the primary care office.
Related codes
Terms used here — Prior Authorization · Out-of-Network · Denial
How we handle it — Prior Authorization · Denial Management · Eligibility Verification
Primary sources
The rules behind CO-38, at the bodies that publish them.
- PECOS Medicare enrollment (opens in a new tab)
Centers for Medicare & Medicaid Services — Where Medicare provider enrollment is filed and maintained. Revalidation deadlines missed here stop payment outright.
- NPI Registry (NPPES) (opens in a new tab)
Centers for Medicare & Medicaid Services — Public lookup and management for National Provider Identifiers. A stale NPPES record is a quietly common cause of enrollment and claim rejections.
- Medicare Claims Processing Manual (opens in a new tab)
Centers for Medicare & Medicaid Services — The operative manual for how Medicare claims must be coded, submitted, adjusted and appealed. When a payer policy and a vendor's advice disagree, this settles it.
Looking for a different code? Search all 190 CARC and RARC codes
Questions about CO-38
Often, within a window the plan defines — commonly thirty to sixty days from the date of service. It requires the primary care physician to issue it retroactively, which most will do for a patient they genuinely referred informally. Ask before appealing, because it is faster and more reliable.
Because payment flows to the rendering provider, so the rendering provider absorbs the denial even though the referral was the primary care physician's to issue. This is exactly why confirming the referral at scheduling, rather than trusting that one exists, is the only effective protection.
Rarely. Referral requirements are characteristic of HMO and point-of-service designs. A PPO producing this code usually signals either a plan misidentified at verification or a specific service carrying its own authorisation requirement independent of the network structure.
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