Appendix E — Denial Codes and What to Do About Them

This is the page to keep open while you work a queue. It collects the group codes, the reason codes, and the remark codes this book uses, and — the part that matters — what to do about each one. Not what it means. What to do.

Because the most expensive mistake in denial management is not misreading a code. It is working every denial the same way. Chapter 28 §28.4 puts four adjustments side by side and shows four completely different next actions, only one of which is an appeal. Chapter 21 §21.11's six-way edit triage has three branches that say do not appeal. A practice that routes everything to one queue and writes letters is doing most of it wrong, expensively, and with the best of intentions.

⚠️ Read this before you use the tables. CARCs and RARCs are national code lists maintained by external committees, and they change. The claim adjustment reason codes are maintained through the X12 Claim Adjustment Status Code Maintenance Committee; remark codes are maintained on their own cycle. Codes are added, retired, and — most dangerously — reworded. Every meaning below is a paraphrase written to teach, not the official text.

Verify the current code text at the source before you quote it in an appeal, and never quote a textbook's wording back to a payer. The list is published and free.

E.1 First: is there anything to appeal?

Nothing in this appendix matters until you have answered this, because the answer decides whether appeal rights exist at all.

A DENIAL is an adjudication decision. The payer received the claim, processed it, and decided not to pay. It has a claim number, a reason code, and appeal rights with deadlines.

A REJECTION is a claim that never arrived. It failed at the clearinghouse or the payer's front end. There is no decision, nothing to appeal, and the timely filing clock never stopped (Chapter 29 §29.1).

⚠️ Confusing the two produces either a duplicate or an unappealed loss — and a practice where one person works both, off one report, will make the mistake regularly. A question offering "appeal it" for a front-end rejection is offering an action that does not exist.

One remark code says this out loud: RARC MA130 — the claim contains incomplete or invalid information, and there are no appeal rights. When you see it, stop. Fix the claim data and resubmit if it is fixable; otherwise close it, categorize it, and do not leave it in the queue (Chapter 29 §29.5).

E.2 The four group codes — who owes the dollar

Every adjustment on a remittance has three parts: a GROUP CODE (who bears it), a CARC (why), and an AMOUNT. A RARC may be attached and carries no amount of its own.

The group code decides WHO OWES. The CARC decides WHY.

They are different questions and the group code is the consequential one, because it is the field that moves money between your accounts receivable and a person (Chapter 28 §28.3).

Three things follow.

A CO adjustment is the contractual adjustment — the spread between your charge and the allowed amount. You agreed to it, and billing the patient for it is a contract violation and frequently worse.

A PR adjustment creates a patient balance, and the CARC tells you which kind: PR-1 deductible · PR-2 coinsurance · PR-3 copay.

And the same denial can arrive under different group codes at different payers. A service denied as not medically necessary may arrive as CO — you may not bill the patient, because no advance beneficiary notice was obtained — or as PR, where the payer has determined the patient is liable. The ABN and the liability modifiers GA/GX/GY/GZ are precisely how you told the payer in advance which it should be (Chapters 22 §22.9, 28 §28.3, and Appendix B §B.10).

⚠️ Posting a group code from a rule instead of from the remittance is damaging in both directions.

PR posted as CO — you have written off a balance the patient owed. Nobody will ever bill it and nobody will ever notice, because a contractual adjustment is exactly what a contractual adjustment looks like. Silent revenue loss with no error message.

CO posted as PR — you have billed a patient for money your contract says they do not owe. This one is visible, because the patient will call, and it is worse: a contract violation, possibly a violation of state balance-billing protections, and at scale a compliance matter rather than a billing error.

The check that finds both, and almost nobody runs it: pull a month of adjustments by group code and reason code and look for any CARC appearing under more than one group code. Where one does, one of the two is being posted from a rule rather than from the remittance.

E.3 The claim adjustment reason codes

Paraphrased meanings. The rightmost column is the action when the code arrives on its own — always subject to §E.5's triage and to what the RARC beside it says.

E.4 The remittance advice remark codes

A RARC carries no amount. It is the sentence that makes a CARC actionable.

CO-16 alone is unactionable. CO-16 with its RARC is a work item.

"Lacks information needed for adjudication" tells you nothing; the RARC names the missing element. And a remittance report that shows CARCs and suppresses RARCs — many do, by default — converts every CO-16 into a phone call. Check your report's configuration once. It is a settings problem masquerading as a payer problem (Chapter 28 §28.4).

E.5 The ninety-second triage — run this before you work anything

Three frameworks the book built separately, assembled in Chapter 29 §29.4. The point is not that it wins appeals. Its value is that it stops you writing the ones that cannot be won.

   BEFORE YOU WORK A DENIAL, ANSWER IN ORDER:      (Chapter 29 §29.4)

   ── 1 ── WHICH OF THE FOUR?  (Ch. 20 §20.10)
      bundled ................... nothing to appeal. Remove the charge.
      not a benefit at all ...... notice and liability modifiers.
      not recognized by this
        payer ................... use the code that payer has.
      not necessary AS
        DOCUMENTED .............. ►► THE ONLY ARGUABLE ONE

   ── 2 ── IF IT IS AN EDIT, WHICH BRANCH?  (Ch. 21 §21.11)
      indicator 0 ............... DO NOT APPEAL
      indicator 1, docs support . APPEAL, quoting the Policy Manual
      indicator 1, docs do not .. DO NOT APPEAL — correct the claim
      MAI 2 ..................... DO NOT APPEAL
      MAI 1 or 3 ................ workable
      proprietary ............... GET THE POLICY FIRST

   ── 3 ── IF IT IS NECESSITY, WHICH KIND?  (Ch. 22)
      CODED WRONG ............... fixable. Correct and resubmit.
      NEVER GOING TO BE
        COVERED ................. not fixable by coding. The
                                  question is whether the patient
                                  was told in advance.

Three of the six edit branches say DO NOT APPEAL — indicator 0, indicator 1 where the documentation does not support the distinction, and MAI 2. A billing office that internalizes that will redirect a substantial amount of effort from letter-writing to charge correction, which is faster, cheaper, and correct (Chapter 21 §21.11).

And the necessity test is answerable in the two minutes it takes to open the policy (Chapter 22 §22.11):

   CODED WRONG                    NEVER GOING TO BE COVERED
   ───────────                    ─────────────────────────
   The record supports the        The record does not contain
   service; the claim does        what the policy requires.
   not reflect the record.
                                  An appeal argues about a record
   FIX: correct the claim.        that says what it says.

   An appeal is appropriate       FIX: change the facts, then
   and frequently succeeds.       resubmit — or accept that the
                                  service is not covered.

Account 10-5502 is the worked case for the right-hand column. The payer's policy required six weeks of documented conservative therapy; the record documented four weeks of NSAIDs and a patient report of physical therapy. Four is not six, and a report is not documentation. Three rounds of appeal letters cannot change what the record says. The fix is a phone call, four more documented weeks, and a resubmission.

The discipline is symmetrical (Chapter 30 §30.1). Do not appeal what cannot be won — and do not write off what can.

E.6 The taxonomy: seven families, and who owns each

Three observations, and the first is the whole argument of Part VI (Chapter 29 §29.2):

• The rightmost column is the point. Four of the seven are not the coder's. Eligibility and authorization denials alone routinely outnumber every coding denial combined.
• The categories are not equally winnable. A documentation denial can be argued if the record supports it. A timely filing denial generally cannot. A duplicate is usually a workflow artifact, resolved rather than appealed.
• And one category is a liar. "Duplicate" frequently means somebody else's claim.

The tell for an eligibility denial is that nothing about the claim is wrong — it is a correct claim sent to the wrong place, or to the right place at the wrong time.

Hard or soft, preventable or not

HARD versus SOFT describes whether the money can still be obtained. A soft denial is recoverable; a hard denial is not, and the amount becomes a write-off. PREVENTABLE versus NON-PREVENTABLE describes whether the practice could have stopped it.

                      PREVENTABLE          NOT PREVENTABLE
                 ┌────────────────────┬────────────────────┐
      SOFT       │ missing modifier   │ payer edit you     │
   (recoverable) │ wrong POS          │  cannot predict    │
                 │ authorization on   │ retroactive        │
                 │  file, not on the  │  eligibility       │
                 │  claim             │  change            │
                 ├────────────────────┼────────────────────┤
      HARD       │ TIMELY FILING      │ genuinely          │
   (dead)        │ no authorization   │  non-covered       │
                 │  obtained          │  service           │
                 │ ►► THE EXPENSIVE   │ patient not        │
                 │    QUADRANT        │  eligible, ever    │
                 └────────────────────┴────────────────────┘

The bottom-left quadrant is where a practice loses money it never had a chance to argue for.

Two things this grid is not. "Preventable" does not mean somebody was careless — it means a process could have stopped it, and Chapter 29 §29.3 says so twice because misreading it as blame is the largest cause of under-reported prevention data in real practices. A category nobody will admit to is a category nobody can fix. And a denial can be non-preventable and still be your problem to work, or preventable and still have been handled correctly at every step.

A soft denial left unworked becomes a hard one. The deadline is the only difference — which is why the work queue is ordered by deadline and not by dollar.

E.7 Working a denial in order

   SORT THE QUEUE BY:                              (Chapter 29 §29.5)

   1.  DEADLINE          ► a soft denial becomes a hard one
                           on a date. Nothing else can do that.
   2.  CATEGORY          ► work like with like. Twelve denials
                           of one kind are one investigation,
                           not twelve.
   3.  DOLLAR            ► within a category, within a deadline.


   THEN, FOR EACH ONE:

   1. READ THE REMITTANCE — group code, CARC, RARC, amount.
      Not the software's summary. The codes.

   2. RUN THE TRIAGE — §E.5. Ninety seconds. Most of the time
      it ends here, correctly, with "do not appeal."

   3. CLASSIFY THE ROOT CAUSE — before doing anything about it,
      because afterwards you will remember the remedy.

   4. DECIDE: appeal · correct and resubmit · close · escalate.

   5. ACT, and record what you did AND what caused it.

   6. IF THE PATTERN IS LARGER THAN THIS CLAIM, SAY SO —
      to somebody who can change the process.
      "Report a pattern, not an instance."

Step 3 before step 4 is the whole discipline. The REMEDY is what you do about this claim. The ROOT CAUSE is what produced it, and one missing-modifier remedy can have five different causes: training · a documentation template · a scrubber edit · an external change (the payer revised its policy) · or maintenance — a chargemaster problem wearing a claim's clothes (Chapter 26 §26.5).

The root-cause categories

   REGISTRATION / ELIGIBILITY ...... Ch. 24
   AUTHORIZATION ................... Ch. 24 §24.6
   CREDENTIALING / ENROLLMENT ...... Ch. 25 §25.7 — NOT fixable by billing
   CODING — CODE SELECTION ......... Chs. 13, 19
   CODING — MODIFIER ............... Ch. 14
   CODING — UNITS .................. Ch. 20 §20.3
   EDIT — NCCI / MUE ............... Ch. 21
   EDIT — PROPRIETARY PAYER ........ Ch. 21 §21.11
   DOCUMENTATION ................... Chs. 4, 22
   CHARGEMASTER / MAINTENANCE ...... Ch. 26 §26.5
   CLAIM DATA (non-clinical field) .. Chs. 25, 26
   TIMELY FILING ................... Ch. 27 §27.7
   COVERAGE / BENEFIT .............. Ch. 22
   DUPLICATE / WORKFLOW ............ Ch. 29 §29.6
   PAYER ERROR ..................... Ch. 28 §28.8

Three rules for using it (Chapter 29 §29.4). One category per denial, chosen deliberately. "Credentialing" is on the list because it is not fixable by billing — resubmitting will not change it, and a queue that keeps returning it to a biller is generating labor that cannot succeed. And "payer error" must be available, because Chapter 29's Case Study 1 is a root-cause list with no row for it: seven of the list's eight rows described something the practice did, so the system could only ever conclude the practice was at fault. A measurement system with a missing category does not report "unknown." It reports the nearest available answer.

Correcting rather than appealing

Both errors produce a DUPLICATE, not a correction — and the original problem is still unfixed (Chapter 29 §29.6, Appendix D §D.9).

⚠️ Correcting is not appealing. A corrected claim says here is different information. An appeal says your decision was wrong about the information you had. At some payers, submitting a corrected claim in place of an appeal closes the original determination and forfeits the appeal rights attached to it (Chapter 30 §30.1). When the claim was right as submitted, do not "fix" it.

E.8 If you do appeal

What every appeal must contain (Chapter 30 §30.2):

   1  IDENTIFICATION      the claim number, the member, the date of
                          service, the line and code at issue.
   2  THE DETERMINATION   what you are appealing: the determination
                          date and the reason code.
   3  THE REQUEST         specific and small: "reprocess line 1 and
                          pay at the contracted allowed amount."
                          Not "review this claim."
   4  THE ARGUMENT        why the decision was wrong — argued
                          against the payer's own standard.
   5  THE EVIDENCE        the documents that prove it, listed and
                          enclosed. Only those documents.
   6  TIMELINESS +        inside the window, at the correct level,
      CHANNEL             through the address or portal the payer
                          designates FOR APPEALS.

Two field notes. Item 3 is where good arguments go to waste — ask for something specific. And item 6 is two requirements wearing one number: an appeal mailed to the claims post-office box is frequently scanned, matched to the claim, and treated as correspondence — or worse, as a duplicate claim. It does not toll anything.

And the amount at issue is the ALLOWED amount, not the charge. On Account 10-4471 the payer's CO-45 priced the visit before CO-97 removed it, so the appealable amount is \$128.40, not \$185.00. An appeal demanding the charge argues against the contract as well as the edit, and the contract argument loses (Chapter 30 §30.1).

The two ladders

Commercial (Chapter 30 §30.5) — there is no single system. There is a contract, a provider manual, state law, and, for self-funded plans, a federal statute, stacked in that order. Most payers offer one or two internal levels: level one inside the claims or appeals unit, level two a fresh review by someone not involved in level one, often with a clinical reviewer. Windows of 60 to 180 days from the determination are common for level one (typical range; your contract governs), and every window runs from the date of the determination being appealed — which is a fact you read off the remittance, not a fact you remember. Ask whether the plan is self-funded and write the answer in the account notes, because an ERISA plan follows the federal claims-procedure rules rather than state insurance law.

Medicare (Chapter 30 §30.6):

   THE FIVE LEVELS OF MEDICARE APPEAL  (Part A / Part B claim appeals)

   LEVEL  WHO DECIDES                    FILE WITHIN         DECIDES IN*
   ─────  ─────────────────────────────  ──────────────────  ───────────
     1    REDETERMINATION                120 days from       60 days
          the MAC — a fresh look by      the initial
          the contractor that decided    determination
   ─────  ─────────────────────────────  ──────────────────  ───────────
     2    RECONSIDERATION                180 days from the   60 days
          the QIC — an independent       redetermination
          contractor, on the record      decision
   ─────  ─────────────────────────────  ──────────────────  ───────────
     3    ALJ HEARING                    60 days             90 days*
          an administrative law judge    ► amount in
          at OMHA — the first level        controversy
          outside the claims world         required
   ─────  ─────────────────────────────  ──────────────────  ───────────
     4    MEDICARE APPEALS COUNCIL       60 days             90 days*
          Departmental Appeals Board
   ─────  ─────────────────────────────  ──────────────────  ───────────
     5    JUDICIAL REVIEW                60 days
          federal district court         ► higher amount
                                           in controversy

   * statutory standards. Amount-in-controversy thresholds adjust
     annually — verify the current figures at CMS/OMHA before
     relying on them.

Three structural facts. The ladder must be climbed in order, and the windows are not symmetrical: 120, then 180, then 60, 60, 60. The amount in controversy starts at level 3, not level 1 — a redetermination has no minimum dollar amount. And for a working practice, levels 1 and 2 are the whole game.

⚠️ The record substantially closes at level 2. The QIC's review is on the record, and the regulations require a reconsideration request to present all the evidence the appellant wants considered; evidence introduced later can be excluded absent good cause. Assemble the reconsideration as if it were the hearing, because evidentially, it is (Chapter 30 §30.7).

And one instrument that is not on either ladder. External review by an independent review organization is a statutory right for non-grandfathered commercial plans, for denials turning on medical judgment — medical necessity, appropriateness, level of care, experimental or investigational determinations — with four months from the final internal adverse determination to request it, and a decision that binds the plan. It is not for a pricing dispute, a bundling edit, a timely-filing argument, or a contract-interpretation fight (Chapter 30 §30.9).

E.9 Account 10-4471's denial, end to end

(Constructed teaching example.) The single worked case this book returns to, and every step of it is in this appendix.

   THE REMITTANCE, DAY 17

   LINE 1   99214-25   CHG 185.00   PAID   0.00
              CO   45    56.60      ◄── the contract. Nothing to appeal.
              CO   97   128.40      ◄── the denial. THE APPEALABLE AMOUNT.
              RARC N19              ◄── "incidental to the primary procedure"

Read together, the payer has said: "the office visit was part of the injection."

And the denial log entry reads "preventable: YES" on a claim that was correct at every step and won on appeal, which is the hardest idea in Chapter 29 and is stated there twice: "preventable" means a process could have stopped it — not that anyone was wrong.

⚠️ The thing to notice about the remittance, because it is the most expensive posting error in the book. The account did not look broken. Three lines paid, the arithmetic balanced, an electronic funds transfer arrived. A posting process that recorded "payment received" and moved on would have been telling the truth. Posted as a contractual adjustment, the \$128.40 disappears — the account zeroes out, nothing ages, no denial is logged, and nobody appeals a write-off.

E.10 The numbers, and the one trap in them

A denial log needs these fields, and two of them are the ones practices leave out (Chapter 29 §29.7):

   date of service · date of denial · payer · provider ·
   CODE and MODIFIERS · CHARGE and ALLOWED ·
   group code · CARC · RARC ·
   ROOT CAUSE CATEGORY ·
   PREVENTABLE? ·
   action taken · outcome · DATE RESOLVED

The two missing ones are root cause category and outcome — and without them the log records activity rather than results.

⚠️ The denominator problem

"Denial rate" is not one number. It is a family of numbers that differ by a factor of two or more, and two practices comparing rates are frequently comparing different things.

Lines or claims? Account 10-4471 is one claim with one denied line of four — 100% by claim, 25% by line. Zero-pay only, or any non-contractual adjustment? A line paid at a reduced rate under CO-151 was partially denied, and counting only zero-pay lines misses it entirely. And what is the denominator — everything adjudicated, or everything submitted? Submitted includes claims still in process, which makes a recent period look better than it is.

Pick one definition, write it down, and never change it silently. Report lines, not claims, for operational work. And be extremely careful with external benchmarks, which are comparisons of definitions at least as much as of performance (Chapter 29 §29.7).

Chapter 29 §29.7 publishes Northgate's measured figures for one month — the denial rate, the share that was preventable, and an appeal overturn rate of 68%, meaning the practice wins roughly two of every three appeals it decides to file. Registration and authorization together account for the largest share of its denials by a wide margin, which is the front end's argument arriving as data.

What that overturn rate is of, and whether filing is always worth it, is not this appendix's question and not this chapter's. Chapter 30 §30.1 names the inputs and stops. Chapter 40 answers it.

E.11 The part that is not on any table

Every action in this appendix is downstream. By the time a CARC exists, the claim has been submitted, adjudicated, and refused, and somebody is being paid to read a code.

Chapter 29 §29.8 is where the money actually is, and its content is not glamorous: a scrubber edit that catches the pattern before submission · a documentation template that prompts what the payer's policy requires · a front desk that verifies eligibility and captures the second coverage · and a person who owns the acknowledgment report, because a rejection nobody reads is a claim that never existed (Chapter 27's Case Study 1).

And two whole categories in §E.6 belong to the front end, which is a structural fact about this work rather than an exhortation: eligibility and authorization denials routinely outnumber every coding denial combined, and neither is fixable by anyone reading a remittance.

The honest version, and the book has been building to it since Chapter 1: some denials are worth working and some are not, and the ones that are not still cost money — they just cost it somewhere a denial code cannot see. Those have to be prevented, because they will never be worth collecting.

Which of Account 10-4471's denial was which, and where the line falls, is the question this book has been circling. Chapter 40 answers it.

E.12 Before you use any of this in writing

Do not quote this appendix to a payer. Every meaning above is a paraphrase written to teach, and the code lists are maintained by external committees on their own schedules. A CARC's official wording is the wording in force on the date the claim was adjudicated, and it may not be the wording in force today.

Get the current text from the source, cite it as of a date, and keep the remittance. Chapter 28 §28.5's habit applies here more than anywhere: keep the remittance itself, retrievable by claim — every payment dispute in your future is a document-retrieval problem.