Which ICD-10-CM Chapters Carry the Most Excludes1 Notes? A Census of the Tabular List

Important: "5,411 Excludes1 lines" does not mean 5,411 individual excluded codes. A single line can contain a code range or another instruction covering many codes.

Every Excludes note in the FY2027 tabular XML was extracted with the code it is written at, its type, its text, and the code references inside its parentheses. A "line" is one condition in a note block: J17 carries one Excludes1 block containing 23 lines. A "location" is a code, category, block or chapter that carries at least one block of that type.

The totals for FY2027: 5,411 Excludes1 lines at 2,648 locations and 2,529 Excludes2 lines at 1,172 locations. Excludes1 outnumbers Excludes2 more than two to one, which is the opposite of what Claim Check users encounter: in the demand data behind this site more than half of the note conflicts people check are Excludes2, because the Excludes2 notes sit on the high-volume categories.

The reason to count by chapter is that the two note types are not distributed evenly, and the pattern says something about how the classification is built. Section I.A.12 of the Official Guidelines describes Excludes1 as a "pure excludes" note meaning "NOT CODED HERE": the excluded code should not be reported at the same time as the code carrying the note, so the two generally should not appear together. Excludes2 means "Not included here": the excluded condition is simply classified elsewhere and may coexist, so both may be reported. Chapters whose codes exist to be replaced by something more specific lean on Excludes1. Chapters whose codes sit beside related conditions lean on Excludes2.

"Per 1,000 entries" divides the line count by the chapter's order-file entries, so chapters of different size can be compared. "Point outside" counts the Excludes1 lines whose referenced code lies in a different chapter.

Four readings of the table:

• Chapter 18 dominates Excludes1. The symptom chapter has the most Excludes1 lines outright (477) and the highest share pointing to other chapters (77%). Symptom codes exist to be replaced by a diagnosis once one is established, and their notes say so, one condition at a time.
• Density follows the same logic. Per 1,000 entries, the respiratory (525), symptom (495) and blood (462) chapters are the densest in Excludes1. The injury chapter, despite 411 lines, is the sparsest at 8 per 1,000, because its 54,325 entries are mostly seventh-character expansions that carry no notes of their own.
• Two chapters invert the ratio. Among the substantive ICD-10-CM chapters, Chapter 12, skin (113 Excludes1 against 179 Excludes2), and Chapter 19, injury (411 against 468), are the only chapters with more Excludes2 than Excludes1 lines. Their exclusions mostly describe a neighbouring condition the patient may also have: L03's Excludes2 block lists cellulitis of the anal region, ear canal, eyelid, mouth and nose, each classified in its own body-system chapter and each reportable alongside L03 when both are present.
• External causes stay inside their chapter. Only 2% of Chapter 20's 460 Excludes1 lines reference a code elsewhere. The V–Y codes exclude each other, not diagnoses.

The locations carrying the most Excludes1 lines are all "elsewhere" or "unspecified" codes, which is what the chapter pattern predicts.

J17, Pneumonia in diseases classified elsewhere: 23 lines

J17 is a manifestation code, and its Excludes1 block is a list of the pneumonias that have their own combination code in Chapter 1 and must not be reported through J17: "candidial pneumonia (B37.1)", "gonorrheal pneumonia (A54.84)", "pneumonia in anthrax (A22.1)", "pneumocystosis (B59)", "varicella pneumonia (B01.2)", "whooping cough with pneumonia (A37 with fifth-character 1)", and seventeen more. Every one of the 23 lines points into Chapter 1. J17 is reserved for the underlying diseases that do not have such a code.

R52, Pain, unspecified: 20 lines

R52's block opens with "acute and chronic pain, not elsewhere classified (G89.-)" and then reads "localized pain, unspecified type - code to pain by site, such as:" followed by eighteen site codes: abdomen (R10.-), back (M54.9), breast (N64.4), chest (R07.1-R07.9), ear (H92.0-), eye (H57.1), headache (R51.9), joint (M25.5-), limb (M79.6-), and on through renal colic (N23) and "pain disorders exclusively related to psychological factors (F45.41)". Eleven of the twenty lines leave Chapter 18. The note is an instruction to find the site, phrased as an exclusion.

K65, Peritonitis: 17 lines

K65 excludes the peritonitis that belongs to another condition: with appendicitis (K35.-), aseptic and chemical (T81.6), gonococcal (A54.85), tuberculous (A18.31), in syphilis (A52.74), neonatal (P78.0-P78.1), puerperal (O85), following abortion or ectopic pregnancy (O00-O07, O08.0). Nine of seventeen lines leave Chapter 11. The code is for peritonitis that is the diagnosis, not peritonitis that is a complication of something coded elsewhere.

The chapter-level notes

Only two chapters carry an Excludes1 note at the chapter heading itself: Chapter 4 (endocrine) excludes "transitory endocrine and metabolic disorders specific to newborn (P70-P74)", and Chapter 15 (pregnancy) excludes "supervision of normal pregnancy (Z34.-)". Seventeen chapters carry a chapter-level Excludes2 block, most of them listing the same set of ranges: perinatal conditions, infectious diseases, pregnancy complications, congenital malformations, endocrine diseases, injury, neoplasms, and symptoms. Those blocks are the classification saying, once per chapter, that a body-system chapter does not contain the systemic categories a patient may also have.

None of this replaces reading the note at the code. It sets the expectation, so that an Excludes1 on an R code (routine) and an Excludes1 on an S code (rarer, and worth a second look) are read with the right weight.

1. When a Claim Check flag names an Excludes1 on a symptom (R), respiratory (J) or nervous-system (G) code, the likely resolution is that a definitive diagnosis elsewhere on the claim replaces the symptom code. Check whether the flagged pair is symptom plus its diagnosis.
2. When the flag is an Excludes2 on a skin (L) or injury (S–T) code, the likely resolution is that both codes stand. Confirm the patient has both conditions and keep both.
3. When an Excludes1 appears on an external-cause (V–Y) code, the conflict is almost always with another external-cause code, and the fix is choosing the one that describes the event.
4. For the "elsewhere" categories (J17, K65, R52 and their kind), read the whole block. The list is the set of conditions with their own code, and the presence of one of them in the record means the "elsewhere" code is not the right one.
5. To check any figure above, or to work with the notes directly, download the note tables from the MedCoder open-data pack (CC0, linked under Sources): one row per note line with the referenced codes parsed out.

• Reading a chapter-level Excludes2 as a prohibition. Seventeen chapters carry one, and every one of them permits the pair when both conditions are documented.
• Assuming an Excludes1 on an injury code is as routine as one on a symptom code. Injury codes carry fewer Excludes1 lines per code than any other chapter; when one appears it is usually specific and worth reading in full.
• Treating the number of lines as the number of conditions excluded. Ranges such as "R07.1-R07.9" or "E08-E13 with .42" are one line each and cover many codes.
• Stopping at the first line of an "elsewhere" code's block. R52's block is twenty lines long because the answer is twenty different site codes.

All counts are extracted from the CMS FY2027 tabular XML (icd10cm_tabular_2027.xml): each <note> inside an <excludes1> or <excludes2> element is one line, and the code references are the code-shaped tokens inside the note's parentheses. Chapter sizes are order-file entry counts from icd10cm_order_2027.txt. The same extraction run on the FY2026 XML gives 5,407 Excludes1 and 2,520 Excludes2 lines, so the FY2027 update added a net 4 Excludes1 and 9 Excludes2 lines, spread across Chapters 1, 2, 3, 11, 17, 18 and 21. Chapter 17's heading was retitled to "Congenital malformations, deformations, chromosomal abnormalities, and genetic disorders" and its range extended to QA1.

Eighty-three of the 5,411 Excludes1 lines have a parenthetical the extractor could not resolve to a code, most of them constructions like "E08-E13 with .42" or lines that end in a colon and introduce sub-lines; they are counted as lines but not as cross-chapter references, so the "point outside" figures are floors, not ceilings.