Mental Health Billing Denial Codes: Causes, Reading & Strategies

Mental health claims face high denial rates due to coding complexities, documentation gaps, and payer-specific policies. Mental health billing denials are not simple routine claim rejections. Unresolved recurring denials can lead to financial penalties and payment recoupments. This results in demands for the recoupment of payments made on past claims. That is why mental health billing teams need to review with precision before initiating an audit. 

This guide by avenue mental health explains denial codes, root causes, fixes, and prevention systems to help optimize revenue. Group Codes, CARCs, and RARCs guidelines help teams identify who is responsible for the current denial. 

What are Denial Codes?

Denial codes explain why reimbursement fails at the payer level. Each code corresponds to a specific rejection reason the insurance company cites. During claim processing, the insurer issues a Remittance Advice (ERA/EOB) containing the following elements:

• Claim Adjustment Reason Code (CARC): Explains why the claim was adjusted or denied.
• Remittance Advice Remark Code (RARC): Provides additional details or clarification regarding the CARC.
• Group Code: Indicates who bears the financial responsibility, like, CO = Contractual Obligation (i.e., the provider), PR = Patient Responsibility, OA = Other Adjustment, and PI = Payer-Initiated.

What Are Mental Health Billing Denial Codes?

These are adjustment codes commonly encountered by psychologists, psychiatrists, therapists, and behavioral-health billing teams. These codes are present in the ERA/EOB and show the reason for rejection  (such as missing information, authorization, documentation, or coverage). They indicate who is responsible for this denial (provider or the patient). The mental health billing team reviews these codes to correct, resubmit, or appeal. In addition to standard medical billing codes, they include specific denial codes such as;

• Prior Authorization (CO-197), 
• Medical Necessity (CO-50), 
• Benefit Limit Exhausted (CO-119), 
• Provider Eligibility (CO-185), and 
• Telehealth Modifier (CO-4).

How Mental Health Billing Denials Work?

The denial system in mental health billing is like a chain where a claim gets rejected at any step. This billing process begins with booking the patient’s appointment. Prior authorization is verified, and following the session, therapists submit their notes into the EHR. Diagnosis (ICD-10) and procedural (CPT) codes are assigned based on the medical services provided. The billing team then prepares the claim and submits it to a clearinghouse for scrubbing. Data, formatting, or documentation issues cause a claim to be rejected and not forwarded to the payer. 

Claims accepted by the clearinghouse are forwarded to the payer for adjudication. The payer evaluates eligibility, authorization, benefits, coding, medical necessity, and other applicable claim rules. Based on this, a claim is either paid, partially paid, or denied. The outcome appears on the ERA/EOB, where CARC/RARC codes indicate the reason for the decision, and group codes (CO, PR, OA, PI) specify who is responsible for payment. The root cause is identified, and an appeal is filed after making the necessary corrections. The billing team bills the patient and tracks denial trends to prevent recurring errors.

The step-by-step workflow is outlined below.

Patient intake → Eligibility check → Prior authorization → Session and documentation → Coding → Claim scrubbing → Submission → Payer adjudication → ERA/EOB → Payment/denial → Denial management

Denial vs Rejection vs Payment Adjustment

Common Mental Health Billing Denial Codes 

Here are major denial codes that trigger in mental health billing are explained:

A. Denial Codes (Payment withheld or Claim Denied)

B. Normal Payment Adjustments (not denials)

How to Read and Resolve Mental Health Billing Denials

Review mental health denials by starting with the ERA and EOB, then the group code, CARC, and RARC.

Step 1: Check the ERA/EOB Payment Status.

• Read the total paid amount section of the claim. If it is zero, the entire claim is denied. A paid claim can still contain service-line adjustments or denials.
• The 835 ERA contains a claim status code; 

1 = processed as primary, 

2 = secondary, 

4 = denied, 

22 = reversal

• Check both the claim and service-line level, as one CPT code within a claim sometimes is denied while another is paid.

Step 2: Review the Group Code (Who is Responsible?)

Step 3: Check the CARC (Reason Code).

CARC number indicating the reason for an adjustment. Read it in conjunction with the Group Code. For example, CO-197 indicates provider responsibility due to a lack of authorization. Common mental health codes include: 197, 50, 119, 151, 185, 4, 11, 97, and 109. Check the amount; multiple CARCs can appear on a single claim (e.g., PR-3 alongside CO-45).

Step 4: Check the RARC (Extra Detail)

The RARC clarifies the CARC by specifying which document is missing or which rule is applied (e.g., N-series or MA-series codes like N130). CARC explains the “why”; the RARC indicates the “how” or “what is missing”. The actual fix for a CARC issue is difficult to understand without the RARC. The payer may also provide free-text remarks.

Step 5: Compare with the Claim

Match the ERA details against CPT, ICD-10, modifiers, POS, session time, rendering provider, DOS, and authorization number. This is where the root cause is identified (e.g., 45 minutes in the notes, but billed as 90837).

Step 6: Determine the Course of Action

• CO/PR standard adjustments: Usually no action required
• Data or coding error: Correct the claim

• Incorrect denial: Appeal
• Patient responsibility: Patient billing
• Unrecoverable: Write-off (timely filing issue)
• appeal deadline

For example:

Billed $150, CPT 90837, Paid $0

CO-197 (RARC N130)

Interpretation: 

• Payment is $0, resulting in a denial. 
• CO indicates provider liability. 
• CARC 197 signifies missing authorization/pre-certification. 
• RARC is related to reviewing plan benefits. 

Verify whether auth was obtained:

• If yes, submit an appeal or corrected claim with the authorization number
• If no, explore retro-authorization
• Otherwise, write it off.

Denial Codes Explained with Meanings, Fixes, and Prevention

CO-4: Modifier incorrect or missing

• Meaning: A required modifier for the procedure code is missing or incorrect (e.g., telehealth 95/GT).
• Fix: Apply the correct modifier and resubmit the claim.
• Prevention: Configure telehealth modifier rules for each payer within the billing system.

CO-11: Diagnosis mismatch

• Meaning: The diagnosis code and CPT code do not align.
• Fix: Correct the diagnosis and resubmit.
• Prevention: Verify that ICD-10 and CPT codes match during charge entry.

CO-16: Information Missing

• Meaning: A necessary detail is missing from the claim (e.g., NPI, Member ID, Modifier).
• Fix: Refer to the RARC; provide the complete details and resubmit.
• Prevention: Use a checklist to scrub claims before submission.

CO-18: Duplicate Claim

• Meaning: The same claim or service has already been submitted.
• Fix: Check the status of the original claim; do not resubmit when it is already paid or pending.
• Prevention: Check the status before resubmitting. Submit multiple psychotherapy codes for the same day if permitted by the payer’s rules.

CO-22: Other Insurance

• Meaning: Another insurance plan must pay first.
• Fix: Verify COB (Coordination of Benefits) with the patient and bill the correct primary insurance.
• Prevention: Ask the patient about other insurance during intake and verify the payer order.

CO-27: Coverage Terminated

• Meaning: Insurance was not active on the date of service.
• Fix: Check eligibility and bill the correct or new insurance. Bill the patient in case group code is PR or valid written consent/contract permits it.
• Prevention: Verify eligibility at intake and repeat verification according to payer requirements and practice policy. Specially after coverage changes, new plan years, or known insurance updates. 

CO-29: Late Claim

• Meaning: The filing deadline has passed.
• Fix: If it is submitted on time, file an appeal with proof (Clearing House Acceptance Report); otherwise, write it off.
• Prevention: Track filing deadlines and resolve rejections promptly.

CO-31: Patient Not Found

• Meaning: Name, ID, or date of birth did not match the insurance records.
• Fix: Correct the details and submit a corrected claim.
• Prevention: Obtain a copy of the insurance card and verify eligibility during intake.

CO-50: Not Medically Necessary

• Meaning: The payer determined that the submitted service did not meet its medical-necessity criteria.
• Fix: File an appeal with clinical notes and the treatment plan.
• Prevention: Ensure alignment between ICD-10 codes, the treatment plan, and progress notes.

CO-109: Incorrect insurance company

• Meaning: The claim was submitted to a payer that does not cover the service under that contract.
• Example: The medical plan delegates behavioral-health claims to another administrator. 
• Fix: Submit to the correct company.
• Prevention: Confirm the behavioral health payer during the eligibility check.

CO-119: Visit limit exhausted

• Meaning: The applicable benefit maximum has been reached
• Fix: Verify benefits and inform the patient. 
• Prevention: Track remaining visits and inform the patient in advance.

CO-151: Sessions not supported

• Meaning: The submitted information did not support the billed frequency. 
• Fix: File an appeal with the treatment plan and notes.
• Prevention: Document the clinical justification for session frequency in the plan and notes.

CO-185: Provider Ineligible to Perform the Service

• Meaning: The rendering provider is not eligible to perform the billed service.
• Fix: Verify the provider’s enrollment, credentialing, license, specialty, and payer requirements before resubmitting or appealing.
• Prevention: Confirm provider eligibility and payer enrollment before scheduling or billing covered services.

CO-197 / CO-198: No Authorization

• Meaning: Prior approval was not obtained (197), or the number of sessions exceeded the approved units (198).
• Fix: Request retroactive authorization or appeal with proof of authorization.
• Prevention: Track authorization dates and units before each session.

CO-97: Service Included in Another Service

• Meaning: The benefit for the service is included in the payment for another service that has already been adjudicated.
• Fix: Review the related services and payer bundling rules before correcting or appealing the claim.
• Prevention: Check payer bundling edits before submitting related services.

CO-234: Procedure Not Paid Separately

• Meaning: The procedure is not paid separately under the payer’s payment rules.
• Fix: Review whether the service is bundled into another billed procedure.
• Prevention: Verify payer payment policies before billing services that may be included in another procedure.

CO-236: Procedure or Modifier Combination Conflict

• Meaning: The submitted procedure or procedure-modifier combination conflicts with an applicable coding edit.
• Fix: Review the procedure code, modifier, documentation, and applicable coding edit before correcting the claim.
• Prevention: Apply modifiers only when the documentation and payer coding rules support their use.

CO-45: Contractual Write-off (Not a Denial)

• Meaning: Your charge exceeded the contracted rate.
• Fix: Accept the adjustment and verify that the payment matches the contracted rate. 
• Prevention: Keep contracted rates updated in the billing system.

OA-23: Impact of Prior Payer

• Meaning: The secondary payer’s calculation reflects payment or adjustments already made by another payer.
• Action: Compare the primary remittance, COB information, and secondary payer calculation before deciding whether action is required. 
• Fix: Reconcile the secondary remittance against the prior payer’s payment and adjustments. Correct COB information if the adjudication is inconsistent.
• Prevention: Verify COB (Coordination of Benefits) and payer order at intake.

PR-1 / PR-2 / PR-3: Patient Responsibility

• Meaning: Deductible, coinsurance, or copay.
• Fix: Bill the patient the exact amount specified in the ERA/EOB.
• Prevention: Verify benefits prior to the service and collect the copay at the time of the session.

Primary Mental Health Billing Denial Triggers

• Missing therapy documentation
• Incorrect session duration (time-based CPT errors)
• Authorization not obtained
• Eligibility inactive
• CPT–ICD mismatch
• Frequency limits exceeded
• Missing modifiers
• Timely filing deadlines
• Non-covered services
• Coordination of benefits
• Medical necessity
• Incorrect place of service
• Bundling/duplicate services

Proven Strategies to Prevent Mental Health Billing Denials

Eligibility, authorization, demographic, coding, and claim-data errors are preventable sources of mental health claim rejections and denials. The main cause is not the treatment itself; it is related to minor errors. These six simple steps will assist the billing team at every stage.

Step 1: Verify Insurance Before the Visit

Check insurance coverage status before the appointment. using a consistent insurance eligibility verification process.

Verify the following details:

• The insurance is active on the date of service.
• The applicable copay and deductible amounts
• Check that mental health sessions are covered and the limit on the number of sessions
• Whether the patient has an EAP (Employee Assistance Program)
• The accuracy of the insurance company and Patient information

Step 2: Keep a record of authorizations

Maintain a centralized record containing the following details for cases requiring prior insurance authorization:

• Authorization number
• Number of authorized visits
• Number of visits used
• Authorization expiration date
• Number of remaining visits

Start the reauthorization workflow before the existing authorization expires or approved units are exhausted. Set payer-specific alerts based on each plan’s submission requirements.

Step 3: Ensure alignment between diagnosis and CPT codes

Every claim must follow this consistent sequence:

Diagnosis → Treatment → CPT Code → Notes

The diagnosis must justify the need for treatment, and the treatment must correspond to the Diagnosis. The CPT code must reflect the actual duration of the session, and all these details must be clearly documented in the notes. Any discrepancy in this alignment leads to a claim rejection.

STEP 4: Check that the note is complete

Before submitting a claim, ensure the note includes the following:

• Date of service
• Session duration
• Service provided
• Diagnosis
• Reason for treatment
• Therapist’s information and signature

Submit the claim only after the note has been signed and locked.

Step 5: Use the software to check before submitting the claim

The claim scrubbing tool catches errors before the insurance company does, such as:

• Missing information
• Incorrect or outdated codes
• Modifier errors
• Mismatch between CPT codes and diagnoses
• This results in fewer rejected claims and reduces rework.

Step  6: Monitor Rejection Patterns

Don’t stop at simply fixing individual claims. Analyze which combination of insurance company, therapist, CPT code, and rejection reason is repeatedly causing issues. If a specific pattern keeps recurring, the problem isn’t the claim itself, but your workflow. Address the root cause and review this monthly.

Mental Health Billing Denial KPIs

Conclusion:

Mental health denial management starts with reading the Group Code, CARC, RARC, and service-line adjudication together. Authorization failures, eligibility changes, coding discrepancies, coverage restrictions, and documentation gaps require different responses. Billing teams reduce repeat denials by tracking root causes by payer, CPT code, provider, and denial category rather than correcting each claim in isolation. 

FAQs:

What are the top 5 Medical Billing Denial Codes?

 The top 10 Denial codes in medical billing are;

• CO 16: Information missing or incorrect.
• CO 18: Duplicate claim.
• CO 29: Timely filing expired.
• CO 50: Not medically necessary.
• CO 197: Prior authorization missing.

What does denial code CO 297 mean?

Denial code CO 297: Referring provider is not eligible to refer to this service. To solve this, check the referring NPI and insurance enrollment, then resubmit the claim.

What is the denial code CO 27?

CO 27 indicates the patient’s insurance coverage expired by the date of service; please verify eligibility dates and submit the bill to another available insurance.

What does denial code PR 27 mean?

PR 27 indicates the patient’s insurance coverage expired by the date of service, and the patient is financially responsible; therefore, bill the patient directly.

What does denial code CO B13 mean?

CO B13 shows this service has already been paid for under another claim or is included in one; please check the claim history to ensure a duplicate claim was not submitted in error.

What does denial code CO 22 mean?

CO 22 indicates that this service is covered by another insurance carrier; please verify the patient’s primary insurance and bill the correct payer.

What is the denial code CO 109?

CO 109: This claim is not the responsibility of this insurance company; please obtain the correct insurance company’s information and resubmit the claim to them.

Q: What is the denial code CO 297?

Referring to CO 297 means the provider is not eligible to refer to this service; verify the referring NPI and insurance enrollment status, then resubmit the claim.

Q: What is the denial code CO 177?

Code CO 177 indicates the patient was not eligible for insurance coverage on the date of service; therefore, re-verify eligibility or bill the claim to another insurance plan held by the patient.

Q: What is the denial code CO 193?

CO 193 means the insurance company upheld its initial decision not to pay; therefore, if new supporting documentation is available, file an appeal at the next level.

Q: What is the denial code CO 252?

CO 252 occurs when additional documentation is required to process the claim; resubmit the claim with the requested clinical notes or medical records.