Appendix A — The Code Sets at a Glance: ICD-10-CM, CPT, and HCPCS Structure Reference

This is a structure reference, not a code list. It collects, in one place, the architecture of the three code sets this book teaches: how a code is built, what each character does, what the conventions and symbols instruct you to do, and where in the book the reasoning lives. It contains no code you should assign from. Assign from the current year's book or encoder, every time — which is the discipline Chapter 6 §6.10 asks you to build and the one this appendix is designed to support rather than replace.

Use it as a map. When you know what you need but not where it lives — which character carries laterality, which section a code number falls in, which letter family a supply belongs to, what a triangle beside a code means — this is the page. When you need to know whether a specific code is right, close this appendix and open the book.

A.1 The update calendar — read this before anything else

Every code set below is revised on a schedule, and a reference printed in a textbook is a snapshot of a moving object. This is the single most important page in the appendix, and it is first for that reason.

⚠️ The two failures this calendar exists to prevent.

The change that leaves the number alone. A deleted code rejects and you find out immediately. A code whose descriptor was revised while the five digits stayed the same produces no rejection at all — you bill the right number for the wrong service and the claim pays. Chapter 13 §13.5 calls the revision triangle "the silent-error symbol," and the January habit it recommends is to look at every ▲ on the codes your practice actually bills.

And the organization that updates annually while a code set updates quarterly. Chapter 20 §20.1's ⚠️ Where Claims Die: HCPCS Level II changes four times a year and most organizations handle code updates once. The failure is a terminated code still sitting in a chargemaster. The fix is a quarterly calendar entry, and it is genuinely that simple.

Guidelines change too, and separately from codes. Chapter 7 §7.10: check whether a guideline changed, not just whether codes changed. A code that still exists with a new instruction attached to it produces silent errors, because nothing rejects.

A.2 ICD-10-CM — what it is and who maintains it

ICD-10-CM classifies diagnoses, in all settings. ICD-10-PCS classifies inpatient hospital procedures only, and this book teaches it at a structural level in Chapter 33 §33.9.

The Guidelines are not optional. They accompany the code set, they are approved by all four Cooperating Parties, and adherence to them is required when assigning ICD-10-CM codes — a requirement that reaches the HIPAA Transactions and Code Sets rule (Chapter 5 §5.7). Verify the current year's Guidelines and any errata directly from CMS or NCHS.

A.3 The anatomy of an ICD-10-CM code

   ICD-10-CM CODE STRUCTURE                     (Chapter 7 §7.3)

   character:   1     2     3     .     4     5     6     7
                │     │     │           │     │     │     │
                │     │     │           └─────┴─────┘     │
                │     │     │            SUBCATEGORY      │
                │     │     │            etiology, site,  │
                │     │     │            severity,        │
                │     │     │            laterality       │
                │     │     │                             │
                └─────┴─────┘                             └── EXTENSION
                  CATEGORY                                    (7th character)
                                                              episode of care,
                                                              fetus, and others

   1st character   ALWAYS a letter
   2nd character   ALWAYS a number
   3rd character   number OR letter   (C4A, D3A, M1A, O9A, Z3A all exist)
   4th-6th         number OR letter
   7th             number OR letter

   MINIMUM LENGTH:  3 characters
   MAXIMUM LENGTH:  7 characters
   The decimal point sits after the 3rd character, always.

A three-character category is a valid code only if it has no further subdivision. Some have none — I10, essential hypertension, is complete at three characters. Most categories do subdivide, and where they do, the three-character category is not a valid code and will reject.

   READING A CODE — M25.561, pain in right knee     (Chapter 7 §7.4)

   M     2     5     .     5     6     1
   │     │     │           │     │     │
   │     │     │           │     │     └─► 6th character: LATERALITY
   │     │     │           │     │           1 = right
   │     │     │           │     │           2 = left
   │     │     │           │     │           9 = unspecified
   │     │     │           │     │
   │     │     │           │     └───────► 5th character: THE JOINT
   │     │     │           │                 6 = knee
   │     │     │           │
   │     │     │           └─────────────► 4th character: THE PROBLEM
   │     │     │                             5 = pain in joint
   │     │     │
   │     └─────┴─────────────────────────► CATEGORY M25
   │                                         "Other joint disorder,
   │                                          not elsewhere classified"
   │
   └─────────────────────────────────────► CHAPTER 13
                                             M00-M99, musculoskeletal
                                             system and connective tissue

   READ AS A SENTENCE, OUTWARD FROM THE CATEGORY:
   "A joint disorder not classified elsewhere ... specifically pain ...
    in the knee ... on the right."

And the level between chapter and category is the block, which is where a category's neighbors — and its instructional notes — live:

   CHAPTER 13 — M00-M99, musculoskeletal system and connective tissue

      M00-M02   Infectious arthropathies
      M04       Autoinflammatory syndromes
      M05-M14   Inflammatory polyarthropathies
      M15-M19   Osteoarthritis
      M20-M25   Other joint disorders          ◄── M25.561 lives here
      M26-M27   Dentofacial anomalies and other disorders of jaw
      M30-M36   Systemic connective tissue disorders
      M40-M43   Deforming dorsopathies
      M45-M49   Spondylopathies
      ...

A.4 The twenty-two chapters

The organizing logic, and where it breaks (Chapter 7 §7.2). Chapters 6–14 are body systems in anatomical order. Chapters 1–5 are organized by etiology or category of disease and take precedence over the body-system chapters. Chapters 15–17 are organized by the patient — pregnancy, the newborn, the congenital — and carry sequencing priority. Chapter 18 is symptoms. Chapters 19 and 20 are a pair: 19 says what happened to the body; 20 says how it happened. Chapter 21 is everything that is not a disease. Chapter 22 is the newest.

The exam point: H is the only letter covering two chapters — eye and adnexa, then ear and mastoid process.

And the range table doubles as an index to the Official Guidelines. A Guidelines address like I.C.9 means Section I, chapter-specific, ICD-10-CM chapter 9 — circulatory. Chapter 9 §9.2.

A.5 The placeholder X

If a code requires a seventh character and has fewer than six characters, X fills every empty position up to the sixth (Chapter 7 §7.5).

Why: the seventh character must be in the seventh position — not in the next available position — because its meaning is defined by where it sits, not by what follows what.

   THE PLACEHOLDER X                             (Chapter 7 §7.5)

   W19.XXXA  —  Unspecified fall, initial encounter

   W     1     9     .     X     X     X     A
   │     │     │           │     │     │     │
   └─────┴─────┘           └─────┴─────┘     └─► 7th character: A
     CATEGORY W19            PLACEHOLDERS          initial encounter
     unspecified fall        positions 4, 5, 6
                             have no meaning
                             for this code


   T39.1X1A  —  Poisoning by 4-aminophenol derivatives,
                accidental (unintentional), initial encounter

   T     3     9     .     1     X     1     A
   │     │     │           │     │     │     │
   └─────┴─────┘           │     │     │     └─► 7th: initial encounter
     CATEGORY T39          │     │     │
                           │     │     └───────► 6th: INTENT
                           │     │                 1 = accidental
                           │     │                 2 = intentional self-harm
                           │     │                 3 = assault
                           │     │                 4 = undetermined
                           │     │
                           │     └─────────────► 5th: placeholder
                           │
                           └───────────────────► 4th: the substance

Notice the difference between the two. In W19.XXXA the placeholder fills three empty positions. In T39.1X1A it fills exactly one, sitting between two characters that both carry meaning. The X is not padding at the end; it holds a position open in the middle.

And the X is not optional. A code missing its placeholders is invalid and will reject.

A.6 The seventh character

The seventh character is an extension, and its meaning depends entirely on where it is used. It is not one concept with one set of values (Chapter 7 §7.6).

Injury, poisoning, and other consequences of external causes — the episode of care

"Initial" does not mean the first visit. "Subsequent" does not mean the second visit. The character describes the KIND OF CARE, not the ordinal position of the encounter (Chapter 12 §12.3).

Four consequences that follow, and each is examined: four active-treatment visits are four encounters coded A; a first visit to a new provider taking over routine follow-up is D; emergency department, then admission, then surgery is all A; and a cast check, a cast removal, and a wound check after closure are each D.

   THE TEST — ask this, never "which visit is this?"    (Ch. 12 §12.3)

              ┌─────────────────────────────────────────┐
              │  Is the patient receiving ACTIVE        │
              │  TREATMENT for this condition?          │
              └──────────────┬──────────────────────────┘
                             │
                ┌────────────┴────────────┐
               YES                        NO
                │                          │
                ▼                          ▼
               "A"          Is the acute phase over, with a
            INITIAL         RESIDUAL EFFECT being treated?
                                     │
                        ┌────────────┴────────────┐
                       NO                        YES
                        │                          │
                        ▼                          ▼
                       "D"                        "S"
                   SUBSEQUENT                  SEQUELA
                 routine healing            the residual
                  or recovery                  remains

A sequela code is not reported alone and is not reported first. Code the residual condition first, then the injury code with S. The S code says "this is a leftover from that." It never says what the leftover is — that is the first code's job.

Fractures — the expanded set (Chapter 12 §12.4)

Some categories expand further, distinguishing open fracture types by a classification of severity and contamination with additional character values. Where the record documents the classification, use it; where it does not, the general open-fracture options apply. This book does not print those values — read them at the category in a current Tabular List.

Four fracture rules, all examined: a fracture not documented as open or closed defaults to closed · a fracture not documented as displaced or non-displaced defaults to displaced · aftercare Z-codes are not used for fracture aftercare (use the acute fracture code with the subsequent-encounter seventh character) · and a pathological fracture is not a traumatic fracture, requiring provider documentation to distinguish.

Elsewhere

Pregnancy uses the seventh character to identify which fetus a condition applies to in a multiple gestation — 0 for a single gestation or where the character does not apply, 1 through 5 for identified fetuses, 9 for other. Other categories use it for other purposes.

You cannot assume the meaning, and you cannot assume the requirement. The seventh character instruction lives at the CATEGORY level in the Tabular List, not at the code. That is one of the reasons the two-step rule exists.

A.7 Laterality

⚠️ The digit assignments are not universal, and neither is the position. They vary between categories. Some use 0 for unspecified and some use 9. Some place laterality in the fifth character and some in the sixth — M25.561 puts it sixth; other categories put it elsewhere (Chapter 7 §7.7). Verify at the category.

The bilateral rule. Where a category does not provide a bilateral option and the condition is bilateral, report both the right and the left codes. Where a category does provide one, use it — reporting right and left separately when a bilateral code exists is an error.

A.8 Finding the code: the two-step rule

Alphabetic Index first. Tabular List second. Always. For your entire career (Chapter 8 §8.1).

What lives in the Tabular and not in the Index: the complete code · seventh-character requirements · Excludes1 and Excludes2 notes · "code first," "use additional code," "code also" · the laterality options · inclusion terms · and block- and chapter-level notes. The Index is a locator. The Tabular is the classification, and where they seem to disagree, the Tabular governs.

   INSTRUCTIONS CASCADE DOWNWARD                      (Chapter 8 §8.4)

  CHAPTER          ┌──────────────────────────────────────────┐
                   │  Chapter-level notes and Excludes.       │
                   │  Govern EVERY code in the chapter.       │
                   └──────────────────┬───────────────────────┘
                                      ▼
  BLOCK            ┌──────────────────────────────────────────┐
                   │  Block-level notes and Excludes.         │
                   │  Govern every category in the block.     │
                   └──────────────────┬───────────────────────┘
                                      ▼
  CATEGORY         ┌──────────────────────────────────────────┐
                   │  Includes, Excludes1, Excludes2,         │
                   │  code first / use additional code,       │
                   │  SEVENTH CHARACTER REQUIREMENT.          │
                   │  Govern every code in the category.      │
                   └──────────────────┬───────────────────────┘
                                      ▼
  SUBCATEGORY      ┌──────────────────────────────────────────┐
                   │  Further notes, further Excludes.        │
                   └──────────────────┬───────────────────────┘
                                      ▼
  CODE             ┌──────────────────────────────────────────┐
                   │  The descriptor. Inclusion terms.        │
                   │  THE PART THE INDEX POINTED YOU AT.      │
                   └──────────────────────────────────────────┘

  THE INDEX DROPS YOU AT THE BOTTOM.
  EVERYTHING ABOVE IT STILL APPLIES, AND YOU HAVE NOT READ ANY OF IT.

The Index's own structure

Main terms are conditions, not body parts. You look up what is wrong, not where it is wrong — which is why looking up Knee returns see condition. Main terms can also be a noun describing the encounter (Encounter, Examination, Screening, Aftercare, History), an eponym, or an abbreviation.

Subterms are indented, and indentation level is meaning. Each level narrows the one above it.

Parentheses are permission to ignore; indentation is a requirement to document (Chapter 8 §8.3).

And a code ending in a dash — M25.56- — means the Index cannot finish the job. More characters are required, and only the Tabular has them.

A.9 The conventions

Excludes1 versus Excludes2 — the most consequential pair (Chapter 8 §8.5)

                    EXCLUDES1                      EXCLUDES2
                    ─────────                      ─────────
   MEANS            "NOT CODED HERE"               "NOT INCLUDED HERE"

   THE TWO          cannot occur together          CAN occur together
   CONDITIONS

   MAY YOU          NO — never both                YES — both, when both
   REPORT BOTH?                                    are documented

   IF YOUR          you have the WRONG code        you may need BOTH codes
   PATIENT HAS
   THE EXCLUDED
   CONDITION

   MEMORY AID       ONE means ONE of them          TWO means you may need TWO

The Excludes1 exception, and it is narrow. The Official Guidelines address the case where an Excludes1 note pairs two conditions that are unrelated in a particular patient; where they are genuinely unrelated, both may be reported despite the note — and where there is doubt about whether they are related, the guidance directs you to query the provider. The safe habit: an Excludes1 note means stop, and the exception is something you establish affirmatively rather than assume.

Excludes2 is permission, not prohibition.

The instructional notes

"Code also" is the one people misread. It does not mean "you may also want to consider." It means two codes are needed — and it deliberately declines to tell you which goes first, because that depends on which condition was the reason for the encounter (Chapter 8 §8.6).

   THE MATCHED PAIR, IN PRACTICE                      (Chapter 8 §8.6)

  ┌─────────────────────────────────────────────┐
  │  THE ETIOLOGY CODE                          │
  │  "Use additional code to identify ..."      │
  │                                             │
  │      ────────────────────────────────►      │  sequenced FIRST
  └─────────────────────────────────────────────┘
                      │
                      │  the same relationship,
                      │  documented from both ends
                      ▼
  ┌─────────────────────────────────────────────┐
  │  THE MANIFESTATION CODE                     │
  │  "Code first the underlying disease"        │
  │                                             │
  │      ◄────────────────────────────────      │  sequenced SECOND
  └─────────────────────────────────────────────┘

  IN THE INDEX, the manifestation code appears in BRACKETS after
  the etiology code — which is the index's way of showing you the
  pair and the order at once.

The alternative to the pair is a combination code — one code classifying two diagnoses, or a diagnosis with an associated manifestation or complication. When a combination code exists and fully describes the condition, use it (Chapter 7 §7.8). And remember what it does: a combination code asserts a relationship.

NEC and NOS — they point in opposite directions

   NOS  —  the DOCUMENTATION isn't specific            (Chapter 8 §8.7)
           "knee pain"  →  which knee?  →  unspecified

   NEC  —  the DOCUMENTATION is specific, the CODE SET isn't
           a precisely named condition with no category of its own
           →  "other specified ..."

   These point in OPPOSITE directions, and only one of them
   can be fixed by a query.

NEC blames the book. NOS blames the note. The practical tell: a descriptor saying "other" is usually NEC; "unspecified" is usually NOS. Only NOS can be fixed by a query.

Punctuation

Brackets are the one to be careful with, because they mean two different things in the two books (Chapter 8 §8.8). Two further conventions live here: "and" means "and/or", and "with" means "associated with" or "due to" — the second of which is large enough that Chapter 9 §9.7 owns it. "See" is mandatory; "see also" is advisory.

A.10 The three specialty tables

Each is organized differently from the main Index, and each has its own trap (Chapter 8 §8.9).

The three column definitions that decide the drug table (Chapter 12 §12.6): poisoning — the drug was taken incorrectly (wrong substance, wrong dose, wrong person, or taken against instructions with alcohol or another drug); adverse effect — the drug was taken correctly as prescribed and produced a harmful effect; underdosing — less was taken than prescribed or instructed.

Two traps. A colon polyp is not automatically benign — the behavior comes from the pathology report, not from the word "polyp." And a table is a starting point: you still verify in the Tabular, which is where the seventh character the table does not show is waiting.

External cause codes carry five axes — cause · intent · place of occurrence · activity · status — and three rules (Chapter 12 §12.7): they are never first-listed, ever · place, activity, and status are reported once, at the initial encounter, while cause and intent carry seventh characters and are reported as long as the injury is treated · and ICD-10-CM itself does not require them. Reporting requirements come from state mandates, payer requirements, or the provider's own policy.

Intent is a clinical and sometimes legal determination and is emphatically not a coder's inference. You do not conclude an injury was accidental because nothing suggests otherwise, and you do not conclude self-harm because something might.

A.11 The Official Guidelines — the four sections

   THE OFFICIAL GUIDELINES — four sections           (Chapter 9 §9.2)

  SECTION I     Conventions, general coding guidelines, and
                chapter-specific guidelines
                ├─ I.A  CONVENTIONS ......... the Chapter 8 material,
                │                              in the source's words
                ├─ I.B  GENERAL RULES ....... most of Chapter 9
                └─ I.C  CHAPTER-SPECIFIC .... Chapters 10, 11, 12
                                               (and the largest part
                                                of the document)

  SECTION II    Selection of PRINCIPAL DIAGNOSIS
                └─ INPATIENT only .......... Chapter 33

  SECTION III   Reporting ADDITIONAL DIAGNOSES
                └─ INPATIENT only .......... Chapter 33

  SECTION IV    Diagnostic coding and reporting for
                OUTPATIENT services
                └─ physician offices, clinics, hospital outpatient,
                   emergency departments, ambulatory surgery

  ────────────────────────────────────────────────────────────────
  THE STRUCTURAL FACT THAT MATTERS:

  Sections II and III are INPATIENT. Section IV is OUTPATIENT.
  They are separate sections BECAUSE THEY DISAGREE.

Section I applies everywhere. Sections II and III apply to inpatient admissions. Section IV applies to outpatient encounters. Know which setting you are in before you look for a rule.

Two navigation habits worth adopting (Chapter 9 §9.2): search the PDF, do not scroll it; and learn the section numbering as an address — I.C.1 is chapter-specific guidance for ICD-10-CM chapter 1, infectious disease. Cite the address when you record a decision. "Per Section I.C.1.d" is a defensible note; "I remember reading" is not.

A.12 CPT — what it is, who owns it, and why that matters

Current Procedural Terminology describes procedures and services furnished by physicians and other qualified health care professionals. It is HCPCS Level I, and it is maintained by the American Medical Association.

Keep the two committees separate: the Editorial Panel decides what the codes are; the RUC recommends what they are worth (Chapter 13 §13.1).

Three consequences of the copyright. A current edition costs money annually — a prior year's edition is a legitimate way to learn the structure cheaply and must never be billed from. Software containing CPT is licensed, which is part of why encoders and clearinghouses cost what they do. And this book cannot reproduce the code set, which is why every descriptor here is a paraphrase. Where this book and the CPT book disagree, the CPT book is right.

A.13 Category I, II, and III

Category II codes carry no relative value and are not paid. Reporting them is optional from a payment standpoint and required by some quality programs — which is the distinction Chapter 36 §36.9 works, along with the 1P / 2P / 3P / 8P exclusion modifiers that record why a measure's standard was legitimately not met (Appendix B §B.13).

Category III codes are archived after a defined period — the AMA's stated convention is roughly five years — unless converted to a Category I code or extended. And the rule that surprises people:

If a Category III code exists that describes the service, it must be used INSTEAD OF an unlisted Category I code. That is not a preference. Using the Category III code is how a new procedure eventually gets a permanent one (Chapter 13 §13.2).

The exam version: a code ending in T is Category III · ending in F is Category II · five digits is Category I.

A.14 The six CPT sections and their ranges

The book is not in numeric order. Evaluation and Management appears first and carries the highest code numbers. It was moved to the front because it is the most frequently used section, and the numbering was left alone (Chapter 13 §13.3).

Ranges shift when the code set does. These are the ranges as this book teaches them; the front of a current CPT book carries the current ones, and the numbers at the boundaries move.

Where Account 10-4471's codes live: 99214 in Evaluation and Management; 20610 and 36415 both in Surgery — which surprises people about a venipuncture and is a useful reminder that the sections are organized by the code set's own logic rather than by how a service feels.

A.15 The CPT symbol set

Symbol sets vary slightly between editions and publishers, and additional symbols exist — including markers for products pending regulatory approval. Your book has a symbol key, usually on the inside cover. Find it and read it once (Chapter 13 §13.5).

The two that matter most. The triangle is the one to fear, because the number survives and the meaning changes: nothing rejects, and the claim pays. The number sign is the one that confuses people — CPT resequences codes, placing a code out of numeric order so it sits with its family rather than where its number would put it.

A.16 The CPT structural conventions

The semicolon — the parent-and-child descriptor

   HOW THE SEMICOLON WORKS                          (Chapter 13 §13.10)

   20600   Arthrocentesis, aspiration and/or injection, small joint
           or bursa; without ultrasound guidance
                                 └── everything BEFORE the semicolon is
                                     the COMMON portion

   20604            ; with ultrasound guidance, with permanent
                      recording and reporting
           └── the indented code inherits EVERYTHING before the
               semicolon from the code above it

   READ IT AS:  "Arthrocentesis, aspiration and/or injection, small
                 joint or bursa; with ultrasound guidance, with
                 permanent recording and reporting"

This is the single most common reason a coder assigns a code whose descriptor does not match the service — reading the indented child without the parent it inherits from.

Add-on codes and modifier-51-exempt codes

   TWO LISTS, ONE RELATIONSHIP                       (Chapter 13 §13.7)

   ┌─────────────────────────────────────────────┐
   │  ADD-ON CODES  ( + )                        │
   │  ► never reported alone                     │
   │  ► exempt from modifier 51                  │
   │  ► primary procedures specified             │
   └──────────────────┬──────────────────────────┘
                      │ ALL add-on codes are
                      │ modifier-51 exempt
                      ▼
   ┌─────────────────────────────────────────────┐
   │  MODIFIER-51 EXEMPT  ( ⊘ )                  │
   │  ► do not append modifier 51                │
   │  ► MAY be reported alone                    │
   └─────────────────────────────────────────────┘

   NOT all modifier-51-exempt codes are add-on codes.
   The relationship runs ONE WAY.

CPT publishes both as their own appendix lists. Know they exist and where they are.

"Separate procedure"

A "separate procedure" code is NOT reported when it is performed as part of a more extensive procedure at the same session and same anatomic site. It IS reported when performed independently, or when unrelated to or distinct from other procedures at the same session (Chapter 13 §13.8).

The mental correction that helps: read it as "separate procedure — meaning: only when genuinely separate."

Unlisted procedures and the special report

Each section has unlisted procedure codes, generally ending in 99. Three rules: use them only when nothing else fits, including Category III · they require a special report describing the nature, extent, and need for the procedure plus the time, effort, and equipment involved · and they do not price themselves. An unlisted code has no assigned relative value, which is why a thin special report produces a low payment or a denial (Chapter 13 §13.9).

Section guidelines and parenthetical notes

At the front of each of the six sections is a block of guidelines, and at the front of subsections there are further notes. They govern every code beneath them, and almost nobody reads them, because the index does not take you there (Chapter 13 §13.4). The Surgery section guidelines are the most consequential in the book, because they define the surgical package (Chapter 17 §17.1).

Parenthetical notes come in five kinds (Chapter 13 §13.6): cross-references · prohibitions ("do not report X in conjunction with Y") · requirements ("use X in conjunction with Y") · conditional instructions · and deletion notices. A prohibition is a bundling instruction living in the code book itself, independent of the NCCI edit files — and it is binding whether or not an edit exists.

The CPT Index

Unlike ICD-10-CM, the anatomic site is a legitimate entry point in CPT, because a procedure is done to something. Main terms come in four kinds: the procedure or service · the organ or anatomic site · the condition · and synonyms, eponyms, and abbreviations.

A range in the Index is the Index telling you it cannot decide. Never code from the index. Read at the code: the full descriptor including everything after the semicolon, the parenthetical notes, the subsection guidelines, and the symbols (Chapter 13 §13.10).

A.17 HCPCS Level II

HCPCS — the Healthcare Common Procedure Coding System — has two levels. Level I is CPT. Level II is everything else: products, supplies, drugs, equipment, and services CPT does not describe.

Permanent codes are maintained through a public quarterly process with a formal application procedure. Temporary codes — several letter families are entirely temporary — let CMS and other payers establish a code quickly when a permanent one does not yet exist. A temporary code may become permanent, may be replaced by a CPT code, or may simply persist for years.

The letter families

Four things to carry out of that table (Chapter 20 §20.2):

• J is drugs, and it is the family you will use most in almost any outpatient setting.
• E, K, and L are what the patient takes home, and they carry a documentation regime unlike anything else in this book — Chapter 20 §20.5.
• G is Medicare's own vocabulary for services CPT does not describe the way Medicare needs — and it is the family most likely to be terminated out from under a chargemaster. If you audit one letter family against the current file each quarter, audit G.
• S codes are explicitly not Medicare's, and neither are T codes. Never send an S or T code to Medicare. It is a code the payer does not have, and the denial is not appealable, because there is nothing to appeal to.

The J-code rule, which is the one that produces claims

THE DOSAGE IS IN THE DESCRIPTOR. THE UNITS ARE THE ARITHMETIC (Chapter 20 §20.3).

   J1030   Injection, methylprednisolone acetate, 40 MG
                                                 ▲▲▲▲▲
                         THAT is the unit. Not the vial.
                         Not the injection. Not the patient.


   UNITS  =  DOSE ADMINISTERED  ÷  DOSAGE IN THE DESCRIPTOR

A J-code does not mean "this drug." It means a specific quantity of this drug. Where a code exists for the exact dose administered, use it rather than multiplying a smaller one. Too few units is a silent underpayment, paid and invisible; too many is what Chapter 21's medically unlikely edits are built to catch.

And the waste attestation completes the line (Chapter 20 §20.4): JW reports the amount discarded, on its own line, with the discarded units; JZ reports that zero was discarded. A drug line with neither is an incomplete claim.

Where the two levels collide

When CPT and HCPCS both have a code for the same thing, the payer decides (Chapter 20 §20.9) — and Medicare frequently has its own G-code where CPT has a Category I code. This is not a coding puzzle; it is a payer question, and the answer lives in that payer's published materials.

A.18 The three code sets side by side

A.19 What this appendix cannot do

It cannot tell you whether a code is current. Everything above is structure, and structure is durable; the codes are not. Every code named here is named for a teaching purpose and appears in this book's own worked examples — and every one of them should be verified in a current book or encoder before it goes on a claim.

It cannot substitute for the conventions in front of you. The Excludes notes, the seventh-character instruction, the parenthetical, and the section guideline that governs a code are at the code, in the book, in the edition in force on the date of service. That is the whole argument for the two-step rule, and no appendix can perform it for you.

And it does not reproduce either code set. ICD-10-CM and HCPCS Level II are free and you should download them. CPT is a copyrighted work of the American Medical Association; every descriptor here is a short paraphrase written to teach. Where this book and the code book disagree, the code book is right.