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HomeDenial Code HubCO-38
CO-38CO CodeNetworkFrequency: Medium Last Reviewed August 2026 Source: X12 / WPC

CO-38 Denial Code — Services Not Provided by Network Providers

The services on the claim were provided by a provider who is not in the payer network, or a referral from a primary care provider (PCP) was required but not obtained. The payer restricts this service to in-network providers or requires a PCP referral.

Resolution Steps Appeal GuidanceFAQ

Quick Answer

CO-38 means the services were not provided by a network provider or a PCP referral was missing. The payer requires in-network providers or PCP referrals for this service. To fix it, verify the provider is in-network, obtain a retroactive referral, or appeal with documentation.

Official Definition

Services not provided by network/primary care providers.

Code Type
CO — Contractual Obligation
Category
Network
Impact Level
High

What This Code Means

The services on the claim were provided by a provider who is not in the payer network, or a referral from a primary care provider (PCP) was required but not obtained. The payer restricts this service to in-network providers or requires a PCP referral.

Status

Manual Review Needed

Recommended Action

1Review the denial message.
2Research the specific reason for the denial.
3Determine appropriate action based on payer policy.
4Escalate for internal review if needed.

Same standard code · different claim context

How CO-38 can be investigated across specialties

CARCs and RARCs are not separate code sets for radiology, gastro, hospital, or professional billing. The code meaning stays standardized; the claim fields, documentation, payer rules, and next checks change by setting.

Professional / Office

Check CMS-1500/837P fields, rendering/billing NPI, diagnosis, modifier, place of service, authorization, and payer policy.

Hospital / Facility

Check UB-04/837I bill type, revenue code, status, inpatient/outpatient rules, authorization, and line-level ERA detail.

Radiology

Check 26/TC component billing, imaging authorization, medical necessity, site of service, same-day edits, and referring provider data.

Gastroenterology

Check procedure relationships, screening vs diagnostic context, modifiers, pathology/anesthesia relationships, authorization, and payer edits.

Behavioral Health

Check provider credential, behavioral-health carve-out, authorization, units/time, telehealth, place of service, and plan-specific rules.

Therapy / Rehab

Check therapy modifiers, timed units, benefit limits, authorization, plan of care/documentation, and NCCI/payer edits.

DME / Supplies

Check HCPCS, modifiers, same/similar equipment, medical necessity, proof of delivery, authorization, and supplier enrollment.

Lab / Pathology

Check CLIA, ordering/referring data, diagnosis support, frequency, panel bundling, specimen/documentation, and payer medical policy.

Financial Impact

Avg. Denial Rate
3-6% of HMO/EPO claims
Days to Resolve
21–45 days
Appeal Success Rate
40-60%
Revenue Risk
High — often becomes patient responsibility

Should This Go to Coding?

USUALLY NOT CODING

Do not send every denial to Coding. Coding is appropriate only when the resolution requires coding judgment rather than an administrative or payer follow-up action.

Send to Coding When

A CPT/HCPCS, ICD-10, modifier, NCCI edit, code pair, sequencing rule, or documentation-to-code decision must be reviewed.

Do Not Send to Coding When

Eligibility or member ID issue.
COB or wrong payer.
Missing authorization with no coding question.
Timely filing.
Contractual adjustment such as validated CO-45.
Deductible, coinsurance, or copay after secondary coverage is checked.

Simple rule: If you would have to choose, change, or defend a CPT/HCPCS, ICD-10, modifier, code pair, NCCI edit, or documentation-to-code decision, Coding should review it.

Corrected Claim, Reconsideration, Appeal, or Something Else?

RESEARCH FIRST

Use the ERA/EOB, RARC, payer portal, policy, claim history, and internal workflow to decide between corrected claim, reconsideration, appeal, coding review, payer follow-up, patient responsibility, or adjustment.

Corrected claim: use when your original claim data was wrong or incomplete.
Reconsideration: use when the claim was processed but the payer should review it again, often with added information.
Appeal: use when you disagree with the payer decision and have evidence supporting payment.
Do not duplicate: do not send multiple paths at once unless the payer specifically instructs you to.
See payer-specific submission methods

Should I Adjust This Balance?

DO NOT ADJUST YET

Treat the balance as recoverable until research shows otherwise. The goal of insurance collections is to resolve the denial and obtain payment when a valid recovery path exists.

Read the full ERA/EOB, including all CARC and RARC codes.
Review payer portal status, claim history, and prior notes.
Check eligibility, COB, coding, authorization, medical necessity, and payer policy as relevant.
Choose the correct action: corrected claim, reconsideration, appeal, coding review, payer follow-up, patient responsibility, or adjustment.
Adjust only when the reason is confirmed, the claim is not recoverable, and your organization authorizes the adjustment.

Collections rule: A denial code by itself does not automatically mean write-off. Work the claim for payment first when a valid recovery path exists.

What Should My Account Note Say?

4-Part Note Formula

WHAT HAPPENED + WHAT YOU REVIEWED/DID + WHY THAT ACTION WAS CORRECT + WHAT HAPPENS NEXT

General Denial Note

REVIEWED ERA/EOB FOR CO-38. PAYER PROCESSED/DENIED $[AMOUNT] DUE TO [DENIAL REASON + CARC/RARC]. VERIFIED [PORTAL/ELIGIBILITY/CLAIM HISTORY/POLICY/CODING/AUTHORIZATION]. [ACTION TAKEN] BECAUSE [WHY THIS ACTION IS SUPPORTED]. REMAINING BALANCE $[BALANCE]. WILL FOLLOW UP IN [TIMEFRAME] OR NO FURTHER PAYER ACTION REQUIRED.

Adjustment Note

REVIEWED ERA/EOB FOR CO-38. PAYER APPLIED $[AMOUNT] AS [CONTRACTUAL/NONPAYABLE REASON]. VERIFIED FINAL ADJUDICATION, [CONTRACT/POLICY/CODING REVIEW], AND NO ADDITIONAL RECOVERY PATH. ADJUSTED/REQUESTED ADJUSTMENT OF $[AMOUNT] PER ORGANIZATIONAL WORKFLOW. REMAINING BALANCE $[BALANCE]. [FOLLOW-UP OR RESOLVED].

Current decision: DO NOT ADJUST YET. Do not document an action you did not actually perform. Do not say a payment was posted unless you personally posted it.

How to Investigate

Investigation Checklist

Step-by-Step Workflow

1Verify the provider is currently in-network with the payer
2Check if a PCP referral was required and obtained
3Confirm the correct provider NPI is on the claim
4Review the patient plan type (HMO, EPO, PPO)
5Check if the provider network status changed

Common Causes

1
Provider not in the payer network
2
PCP referral not obtained before the service
3
Patient saw a specialist without a referral (HMO plan)
4
Provider in-network status lapsed or was terminated
5
Wrong provider NPI entered on the claim

Related Denial Codes

CO-95CO-197CO-109

Step-by-Step Resolution

If provider is in-network: correct the NPI and resubmit
If referral missing: obtain retroactive referral from PCP
If provider is out-of-network: bill patient or appeal for network gap exception
If provider network status lapsed: contact payer to reinstate
If patient went out-of-network knowingly: bill the patient

Appeal Guidance

Appeal Grounds

The provider is in-network, or a referral was obtained, or a network gap exception applies.

Appeal Letter Template

We are appealing the CO-38 denial. The provider [name, NPI] is in-network with [payer] per the attached enrollment confirmation. Alternatively, no in-network provider was available within [distance] and a network gap exception was requested. We request reprocessing.

Required Documentation Checklist

Provider network enrollment confirmation
PCP referral documentation
Evidence that no in-network provider was available

Real-World Examples

Missing PCP Referral

Won
Situation

HMO patient saw a specialist without a PCP referral. CO-38 returned.

Outcome

Obtained retroactive referral from PCP. Resubmitted. Paid.

Network Gap Exception

Won
Situation

No in-network specialist within 50 miles. Patient saw out-of-network provider. CO-38 returned.

Outcome

Appealed with network gap documentation. Payer approved exception. Paid at in-network rate.

Patient Responsibility

Can you bill the patient?
Yes — with conditions
When
Billable if the patient went out of network without authorization.

If the patient chose an out-of-network provider without authorization, they may be responsible. But if the provider is in-network or a referral was obtained, appeal.

Payer-Specific Notes

Medicare

Medicare does not typically use CO-38 since Medicare patients can see any Medicare-enrolled provider. This is more common with HMO and Medicare Advantage plans.

Commercial

Commercial HMO and EPO plans use CO-38 when patients see out-of-network providers without a referral. PPO plans may have reduced benefits but still cover out-of-network.

Frequently Asked Questions About CO-38

Educational Platform Notice

DenialPro is an educational platform designed to teach medical billing denial management.

Do not submit Protected Health Information (PHI), personally identifiable information (PII), patient names, member IDs, claim numbers, dates of birth, medical record numbers, or confidential healthcare information.

Always verify guidance with official payer policies, CMS guidance, coding guidelines, and applicable regulations.

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