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E66.811 ICD-10-CM Code: Obesity, class 1

Billing Status: YES. This is a valid, specific, and billable ICD-10-CM reference.

Coding at a Glance

Tabular directives
4 Excludes2 · 1 use-additional code · 1 code-first instruction

Inpatient Payment Groups (MS-DRG)

Potential MS-DRG participation — not a DRG assignment.

MS-DRGs this diagnosis helps define, as principal or secondary, per the CMS ICD-10-CM/PCS MS-DRG Definitions Manual v43, Appendix B.

  • MS-DRG 640 — MISCELLANEOUS DISORDERS OF NUTRITION, METABOLISM, FLUIDS AND ELECTROLYTES WITH MCC (MDC 10)
  • MS-DRG 641 — MISCELLANEOUS DISORDERS OF NUTRITION, METABOLISM, FLUIDS AND ELECTROLYTES WITHOUT MCC (MDC 10)

A diagnosis appearing in a group's logic does not by itself determine the DRG assigned to a stay; the grouper uses the full claim.

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for E66.811 in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2026Effective: October 1, 2025

Notes without a marker are published on E66.811 itself; “inherited from” names the category or block whose note applies here.

Excludes2 — Not Included Here

Conditions not covered by this code, but which may be reported alongside it when both are present.

Code First

Underlying conditions that must be sequenced before this code.

  • obesity complicating pregnancy, childbirth and the puerperium, if applicable (O99.21-)

Source: inherited from E66

Use Additional Code

Supplementary codes the tabular list directs you to add.

  • Use additional code to identify body mass index (BMI), if known, for adults (Z68.1-Z68.45) or pediatrics (Z68.5-)

Source: inherited from E66

Coder workflow for E66.811

MedCoder structured workflow — derived from this code’s own official record

Choose the right path

  1. Is the underlying (etiologic) condition the Code First note names documented?
    Yes → Sequence the underlying condition first, then E66.811.
    No → Continue; do not add an underlying condition the record does not document.

    ReviewO99.21

Consider E66.811. Then work the Use Additional Code note, and confirm the code is valid for the date of service in the Verify section.

Documentation check

The provider’s diagnostic statement
Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).
The underlying (etiologic) condition
Named in the Code First note; sequenced before this code when documented (Guidelines I.A.13).
The conditions the Use Additional Code note names
Reported with this code when documented; a conditional instruction (“if applicable”, “if known”) applies only when the record supports it.

Official instructions as workflow

  • Excludes2 — not part of E66.811(4 notes)

    Coding workflow: The conditions named in this note are not included in E66.811. When the record documents both, both may be reported; the note is a boundary, not a prohibition.

    CompareE23.6, E88.2, Q87.11

    See the official tabular notes · Guidelines I.A.12.b

  • Code First — sequencing check(1 note)

    Coding workflow: Check whether the underlying or etiologic condition the note names is documented. When it is, sequence it before E66.811. Do not add an underlying condition the record does not document.

    ReviewO99.21

    See the official tabular notes · Guidelines I.A.13

  • Use Additional Code — after identifying E66.811(1 note)

    Coding workflow: Check whether the documentation supports the additional code(s) the note names, and report them with E66.811 when it does. Where the instruction is conditional (“if applicable”, “if known”), it applies only when the record documents the condition.

    ReviewZ68.5

    See the official tabular notes · Guidelines I.A.13

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

Documentation: The underlying condition the Code First note names is documented alongside this condition.

Coding question: How are the two sequenced?

Path: Review the Code First note.

Reason: The underlying condition is sequenced first and the manifestation follows (Guidelines I.A.13).

ReviewO99.21

Documentation: A condition the Use Additional Code note names is documented.

Coding question: Is a second code reported with E66.811?

Path: Review the Use Additional Code note and the code it names.

Reason: The additional code is reported when the record documents the condition; a conditional instruction applies only when its condition is met (Guidelines I.A.13).

ReviewZ68.5

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Code Overview

Obesity, class 1 is a billable ICD-10-CM diagnosis code (E66.811).

MedCoder summary Summary composed by MedCoder from this code's official ICD-10-CM record. The tabular instructional notes themselves appear verbatim below.

Indexed Clinical Terms (1)

Official source data — entries quoted as published, in the Index’s own lookup phrasing

Clinical term phrases from the official ICD-10-CM Index to Diseases and Injuries that map to this code. These are alphabetic-index entries shown as the Index writes them — lookup phrasing, not necessarily the wording of a final diagnosis.

Official Coding Guidelines

Official source data — quoted verbatim from the CMS/NCHS Official Guidelines

Official source data — quoted verbatim from the CMS/NCHS Official Guidelines

Verbatim excerpts from the ICD-10-CM Official Guidelines for Coding and Reporting (CMS/NCHS) that govern this code.

Chapter 4: Endocrine, Nutritional, and Metabolic Diseases (E00 -E89)

1) Obesity class The obesity class codes in subcategory E66.81, Obesity class, require a fifth character to convey the severity of obesity. The obesity class should be documented in the medical record by the provider for these codes to be assigned. The obesity class codes can be reported with other obesity codes in the classification found in Chapters 4 and 15 to fully describe the condition. However, if both class 3 obesity and morbid obesity are documented, only a code for class 3 obesity should be assigned as it is more specific.

Chapter 4: Endocrine, Nutritional, and Metabolic Diseases (E00 -E89)

b. Obesity The obesity codes in category E66, Overweight and obesity, include codes related to the cause of obesity, such as drug-induced obesity (E66.1), and codes related to effects of obesity, such as code E66.2, Morbid (severe) obesity with alveolar hypoventilation. There are other codes related to obesity in other categories of the classification, such as E88.82, Obesity due to disruption of MC4R pathway; and codes in fifth character subcategory O99.21, Obesity complicating pregnancy, childbirth, and the puerperium.

Decision Points

The directives on this code's own record, as a pre-claim checklist.

  1. Sequencing: 1 Code First instruction — the underlying condition is sequenced before this code when present. See the Code First notes
  2. 1 Use Additional Code instruction — report the named additional code(s) when the documentation supports them. See the Use Additional Code notes
  3. 4 Excludes2 entries — those conditions are not part of this code and may be reported additionally when documented. See the Excludes2 notes

Checklist rows are derived from this code's own official directives; the wording of each check is MedCoder editorial. The official notes themselves are in the sections each row links to.

Verify Before Coding

  • Questionable admission. The Medicare Code Editor lists this among its questionable-admission codes: reported as the principal diagnosis, it is not usually sufficient justification for an inpatient admission on its own, so it flags the admission as questionable. The code itself remains acceptable as principal.

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder structured relationships — computed from published CMS and AHRQ datasets

Other codes that name E66.811 or its code family, from the CMS ICD-10-CM tabular instructional notes. Tabular-note edges are stored at the code family level that carries each note.

Referenced by 1 Excludes1 note: R63.5 — Abnormal weight gain (via E66.-).

These codes’ tabular lists mark this diagnosis as mutually exclusive — not reported together unless the conditions are documented as unrelated.

Referenced by 1 Code First instruction: Z99.3 — Dependence on wheelchair (via E66.-).

Each of these codes carries a Code First note naming this condition — when that code is reported, THIS code is sequenced first, ahead of it.

Referenced by 2 Use Additional Code instructions across 2 chapters: E88.81 — Metabolic syndrome and other insulin resistance (via E66.-), O99.21 — Obesity complicating pregnancy, childbirth, and the puerperium (via E66.-).

These codes instruct coders to additionally report this code when it applies.

Referenced by 1 Code Also instruction: Z15.2 — Genetic susceptibility to obesity (via E66.8.-).

These codes suggest coding this condition alongside when both are present.

MS-DRG Grouper Relationships (FY2026)

Potential MS-DRG participation — not a DRG assignment.

FY2026 MS-DRG: not on the CMS CC/MCC list — as a secondary diagnosis this code does not change MS-DRG severity for that release.

Named in the grouper logic of 2 MS-DRGs: DRG 640 (MDC 10), DRG 641 (MDC 10).

From the CMS MS-DRG Definitions Manual (Appendices B and C). Actual DRG assignment depends on the complete claim.

Clinical classification (AHRQ CCSR):END009 — Obesity (default).

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Related Codes

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical category (Obesity).

E66.01 — Morbid (severe) obesity due to excess calories, E66.09 — Other obesity due to excess calories, E66.1 — Drug-induced obesity, E66.2 — Morbid (severe) obesity with alveolar hypoventilation, E66.8 — Other obesity, E66.812 — Obesity, class 2, E66.813 — Obesity, class 3, E66.89 — Other obesity not elsewhere classified, E66.9 — Obesity, unspecified, E88.82 — Obesity due to disruption of MC4R pathway, O99.210 — Obesity complicating pregnancy, unspecified trimester, O99.211 — Obesity complicating pregnancy, first trimester, O99.212 — Obesity complicating pregnancy, second trimester, O99.213 — Obesity complicating pregnancy, third trimester, O99.214 — Obesity complicating childbirth, O99.215 — Obesity complicating the puerperium, Z68.30 — Body mass index [BMI] 30.0-30.9, adult, Z68.31 — Body mass index [BMI] 31.0-31.9, adult, Z68.32 — Body mass index [BMI] 32.0-32.9, adult, Z68.33 — Body mass index [BMI] 33.0-33.9, adult, +14 more

Same Index main term, other category

The ICD-10-CM Index to Diseases and Injuries files this code under the main term “Obesity”; these codes share that main term but sit in a different category of the Tabular List.

E23.6 — Other disorders of pituitary gland (pituitary), E27.8 — Other specified disorders of adrenal gland (adrenal), E88.82 — Obesity due to disruption of MC4R pathway (due to, gene mutation, leptin), O99.21 — Obesity complicating pregnancy, childbirth, and the puerperium (complicating, pregnancy), O99.214 — Obesity complicating childbirth (complicating, childbirth), O99.215 — Obesity complicating the puerperium (complicating, puerperium), Z71.3 — Dietary counseling and surveillance (dietary counseling and surveillance)

Lab tests where this diagnosis supports Medicare coverage (NCD)

Medicare's National Coverage Determination (NCD) program lists this diagnosis as medical justification for these lab tests.

Lipid Panel

Contextual Map

Every relationship of E66.811 in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run E66.811 with these 5 related codes in Claim Check

Hierarchy

Referenced by Excludes1 notes

Referenced by Code First instructions

Referenced by Use Additional Code instructions

Referenced by Code Also instructions

Clinical classification (CCSR)

MS-DRG Grouper

MDC crossing

  • MDC 10 — Endocrine, Nutritional and Metabolic Diseases and Disorders[MDC crossing]: “Endocrine, Nutritional and Metabolic Diseases and Disorders — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs. 5,008 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2026

Index entries

  • Obesity, class, 1[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026

Nearest codes (13)

Change history

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data
CMS/CDC ICD-10-CM FY2026 tabular list, index and tables, effective October 1, 2025 Release, file and checksum · Publisher’s page
Coding guidelines Official source data
ICD-10-CM Official Guidelines for Coding and Reporting (FY2026), quoted by section Release, file and checksum · Publisher’s page
Claim edits Official source data
CMS Definitions of Medicare Code Edits — v43.1 (April 2026) Release, file and checksum · Publisher’s page
Inpatient payment groups Official source data
CMS MS-DRG Definitions Manual (incl. Appendix B diagnosis index, Appendix C CC/MCC list, Appendix E procedure index) and IPPS Final Rule tables — v43 Release, file and checksum · Publisher’s page
Change history and date-of-service validity Official source data
CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page
Comparisons, relationships and the contextual map MedCoder structured relationship
Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears
Summary and FAQ answers MedCoder explanation
Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates

Cite this page

Reference this page in a research guide, syllabus or article. The release is included because code content changes each year.

MedCoder.ai. "E66.811 — Obesity, class 1." ICD-10-CM FY2026. https://medcoder.ai/icd10/code/e66.811-obesity-class-1

Change history

  • FY2025 — October 1, 2024
    Added to the code set
    Obesity, class 1
    FY2025 changes

Nearest Codes in This Family

Official ICD-10-CM classifications closest to E66.811 in its code family, with their registry titles.

View all codes in the E66 family