How to Read and Answer an Insurance Denial in Private Practice

Before you write anything, do three things: note the date you received the notice, work out whether it's an adjustment code on a remittance or a formal denial of benefits, and put the deadline on your calendar. Most denials in a solo practice are paperwork problems you fix with a corrected claim. The rest have deadlines and rights attached, and you win those by answering the plan's stated reason with the plan's own criteria.

This is general information, not legal or billing advice. The client's plan documents and your payer contract control, and they vary.

First, Figure Out What You're Holding

Denials arrive in two forms. One is a line on a remittance: a paper Explanation of Benefits (EOB) or an electronic remittance advice (ERA), which uses the X12 835 standard.¹ The other is a denial letter, usually addressed to the client, that explains a decision and describes appeal rights.

On a remittance, each adjustment has a group code, a Claim Adjustment Reason Code (CARC) and often a Remittance Advice Remark Code (RARC). CMS describes CARCs as the overall explanation and RARCs as added detail.¹ “CO-50” is group code CO plus reason code 50.

Group codes: who owns the balance

• CO (Contractual Obligation): in Medicare, assigns responsibility to the provider; beneficiaries can be billed only under PR.¹ For commercial plans, your contract says whether you can bill the client.
• PR (Patient Responsibility): assigns the amount to the patient.¹
• OA (Other Adjustment) and PI (Payor Initiated Reduction).²

Reason codes common in behavioral health

These are the X12 definitions, lightly shortened:³

• 4: the procedure code is inconsistent with the modifier used. Check every modifier, including any telehealth modifier, against the payer's billing guide.
• 16: the claim lacks information or has submission or billing errors. X12 requires at least one remark code with it, so find the RARC that names what's missing.
• 29: the time limit for filing has expired.
• 50: non-covered because the payer does not deem the service a “medical necessity.”
• 97: the benefit is included in the payment for another service already adjudicated.
• 167: the diagnosis is not covered.
• 197 / 198: precertification or authorization absent / exceeded.

Remark codes narrow it down. From the X12 list:⁴ M51 is a missing, incomplete or invalid procedure code; N20 means the service isn't payable with another service on the same date; MA130 means the claim is unprocessable and no appeal rights are afforded. An unprocessable claim isn't appealed. You fix it and resubmit.

Triage: Fix It or Appeal It

Ask one question: did the payer misread the claim, or disagree with the care?

Misread it. Wrong member ID, a CPT or modifier problem (CO-4, CO-16 with M51), an authorization you had but didn't put on the claim, a wrong NPI. Send a corrected claim, not a new one. On the CMS-1500 and the 837 that usually means frequency code 7 (replacement of prior claim) with the original claim number; code 8 voids a claim. Premera, for example, warns that a corrected claim not marked as one may be denied as a duplicate.⁵ Follow your payer's own instructions. Medicare handles minor errors and omissions through a reopening, not an appeal.⁶

Disagreed with it. Medical necessity (CO-50), a non-covered diagnosis (CO-167), an authorization denial you believe is wrong (CO-197/198), or bundling you dispute (CO-97). These need a written appeal. For ERISA employer plans, the denial notice must give the specific reason and the plan provision it relied on. If an internal guideline was used, the notice must include it or offer a free copy. For medical-necessity denials, it must explain the clinical judgment or offer that explanation free on request.⁷ If your letter just says “not medically necessary,” ask for those in writing.

Deadlines, and Who Sets Them

Timely filing (CO-29). For commercial plans the filing window comes from your contract or the payer's provider manual, and it differs by payer. Look it up before writing a claim off. If you filed on time, your clearinghouse acceptance report is your evidence.

Group health plans:

• ERISA's claims rules require plans to allow at least 180 days after receipt of an adverse benefit determination to appeal.⁸ HealthCare.gov gives the same 180 days.⁹
• Under the ERISA rules, a plan with one level of appeal must decide a post-service appeal within 60 days and a pre-service appeal within 30 days. If the plan has two levels, each level gets half that: 30 and 15 days. Urgent care appeals are decided within 72 hours.⁸ HealthCare.gov likewise lists 60 days for services already received.⁹
• If the internal appeal fails, HealthCare.gov says external review must be requested in writing within 4 months of the final determination. Standard reviews are decided within 45 days, expedited ones within 72 hours.¹⁰

Other plan types can run on different rules, so use the deadline in the notice or plan documents.

Traditional Medicare. The first level is a redetermination by the Medicare Administrative Contractor. You have 120 days from receipt of the initial determination, which is presumed to be 5 calendar days after the notice date. The request must be written, on form CMS-20027 or in a letter. A decision generally comes within 60 days.⁶

Your network contract. It may have its own provider dispute process, with its own deadline, separate from the client's appeal rights. Read both.

Who Can Appeal

Under ERISA's claims rules the appeal belongs to the claimant, your client, and an authorized representative can act for them. Plans may require a form to establish that. An assignment of benefits does not, by itself, make you the representative. For urgent care claims, the plan must let a health care professional who knows the claimant's condition act as the representative.⁸

So talk to the client first. If you're handling the appeal, get their designation on the plan's form and keep a copy.

What Parity Law Lets You Ask For

Under the Mental Health Parity and Addiction Equity Act (MHPAEA), a plan must provide its medical-necessity criteria for mental health and substance use benefits on request. Participants, beneficiaries and contracting providers can all ask. The plan must also make the reason for any denial available to the participant.¹¹ MHPAEA applies directly to employer group plans with more than 50 employees and to individual-market coverage; small group plans generally have to meet parity through the Affordable Care Act's essential health benefits rules instead.¹² Plans that impose nonquantitative treatment limitations (NQTLs) must produce comparative analyses for regulators on request.¹² The 2024 final rule added a right for participants to get a copy after a mental health denial, and for ERISA plan participants at any time.¹³

The upshot: ask in writing for the medical-necessity criteria, the clinical rationale and any guideline relied on, and free copies of documents relevant to the claim.⁸ For an employer plan, also ask for the comparative analysis for medical-necessity review.

What Goes in a Good Appeal Letter

• Identifiers: client name, date of birth, member ID, claim number, dates of service, CPT code, amount, your NPI.
• The denial reason, quoted exactly, with the codes.
• The plan's criteria, and how the client meets each one. If you don't have them yet, say you've requested them and will supplement.
• Clinical facts that answer the criteria: diagnosis, symptoms, functional impairment, treatment plan, progress, and why this frequency or session length is needed now.
• Supporting documents and a specific request to reprocess and pay.

Send the minimum necessary. HIPAA requires reasonable efforts to limit PHI to the minimum needed for the purpose, and payment disclosures aren't among the exceptions.¹⁷ Send what answers the denial, not the whole chart.

A fill-in-the-blanks template

[DATE]
[PAYER NAME], Appeals
[ADDRESS OR FAX FROM THE DENIAL NOTICE]

Re: Appeal. Member [CLIENT NAME], DOB [DATE], ID [MEMBER ID]. Claim [NUMBER]. Date(s) of service [DATES]. CPT [CODE]. Billed [AMOUNT].

I am writing [as the treating provider / as the member's authorized representative; designation enclosed] to appeal the denial of this claim. The [EOB / letter] dated [DATE] gives reason code [CODE] and states: “[QUOTE THE DENIAL REASON EXACTLY].”

The plan's criteria for [SERVICE], in [NAME AND VERSION OF CRITERIA], require [CRITERION 1], [CRITERION 2] and [CRITERION 3]. The member meets each: [CRITERION 1]: [CLINICAL FACT, DATE, SOURCE DOCUMENT]. [CRITERION 2]: [FACT]. [CRITERION 3]: [FACT]. [WHY THIS LEVEL OF CARE IS NEEDED NOW.]

Enclosed: [TREATMENT PLAN DATED ___], [PROGRESS NOTES FOR ___], [MEASURE SCORES], [AUTHORIZATION OR CALL REFERENCE NUMBER].

I also request, free of charge, the medical-necessity criteria and any guideline relied on, the clinical rationale, and copies of all documents relevant to this claim [EMPLOYER PLAN: and the comparative analysis for medical-necessity review].

Please reprocess and pay claim [NUMBER]. I am available for a peer-to-peer review at [PHONE].

[NAME, CREDENTIALS]
[NPI]
[PRACTICE NAME AND ADDRESS]

Recoupment and Clawback Requests

A recoupment letter means the payer thinks it overpaid and wants the money back, either as a refund or by withholding future payments. Read it for:

• The claims and dates of service involved
• The stated reason
• The amount per claim
• The dispute deadline
• When any offset starts

Then check your network contract for the overpayment dispute process and window. Also check state law. The AMA points physicians to state-by-state recoupment laws and has a sample overpayment appeal letter.²⁰ Which rules apply can depend on plan type. The Harris County Medical Society's Texas overview, for example, describes different look-back rules for fully insured plans, self-insured plans, Medicare and Medicaid.²¹

Don't ignore it and don't just pay it. If the payer is right, refund the money or accept the offset, and fix the cause. If it isn't, dispute in writing before the deadline, claim by claim. Attach your eligibility check, the authorization and the original remittance.

The Day the Letter Arrives: A Checklist

1. Record the date you received it, and keep the envelope or portal timestamp.
2. Decide what it is: remittance code, formal denial, recoupment request or records request.
3. Calendar the deadline, with a reminder two weeks earlier.
4. Pull the claim, remittance, authorization, eligibility check and notes for those dates.
5. Triage: a corrected claim for errors, an appeal for coverage or clinical decisions.
6. If appealing, talk to the client, get the representative form signed, and request the criteria and documents.
7. Draft a letter that answers the stated reason, and attach only what supports it.
8. Send it in a way you can prove, and keep copies.
9. Log every call: date, name, reference number.
10. If the internal appeal is denied, calendar the external review deadline.

Using AI to Read These Letters

AI handles the first read well: what the letter says, what it's asking for, when a response is due, plus a rough draft. It isn't a billing tool. It doesn't know the plan's criteria unless you give them to it, and it can get a code or date wrong. Check codes against the X12 list and dates against the letter.

A denial letter is PHI: name, member ID, dates of service, often a diagnosis. Don't paste it into a consumer AI chatbot. For more, see whether therapists can use ChatGPT under HIPAA. Tools that run on your own computer don't send the text anywhere.

How Hey Eduardo handles a letter like this

Hey Eduardo is a Mac menu-bar app: highlight text anywhere, press a shortcut, and a panel appears over your work. For a scanned letter, press ⌥⇧C and drag a box over it, and Apple's on-device text recognition reads it. ⌥⇧D pulls out dates, figures and names, such as the claim number, amount and deadline.

“What should I watch out for?” reports what the letter commits you to and what expires, based only on the text, with no legal or financial advice. “How do I respond?” drafts a reply you edit and send. It never accepts a deadline or confirms a figure for you. It acknowledges the letter, says you will review it, and writes [...] where it needs a fact the letter doesn't give, like which criteria your client meets. Follow-ups such as “what happens if I miss it?” remember the conversation. Review everything before it goes out.

Local mode is the default. The model runs on your Mac, and nothing captured is sent to Hey Eduardo or any AI company. Cloud mode is opt-in, uses your own API key and is meant for research with no client data. Recent history is on by default and stays on the Mac; for clinical work, turn it off in Settings → Reading → Recent. It doesn't know payer policies and isn't legal advice. More for therapists, psychologists, and in the guide.

Related: What each denial code means · Hey Eduardo for therapists · Hey Eduardo for psychologists · Can therapists use ChatGPT under HIPAA? · The Hey Eduardo guide