2027 ICD-10-CM Diagnosis Code R40.2ANontraumatic coma due to underlying condition

ICD-10-CM Codes›R00–R99›R40-R46›R40

ICD-10-CM R40.2A
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

R40.2A is a billable ICD-10-CM diagnosis code for nontraumatic coma due to underlying condition. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 80 through 81, 791, 793. As a secondary diagnosis, it counts as a major complication or comorbidity (MCC) and places an inpatient stay in the highest severity level of its MS-DRG family. It does not count, however, when the principal diagnosis is one of 718 closely related codes. The code is not accepted as a principal diagnosis by the Medicare Code Editor. As a symptom code, it should not be used as a principal diagnosis once a related definitive diagnosis has been established. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Coma; stupor; and brain damage.

For Medicare Advantage risk adjustment, R40.2A maps to CMS-HCC Category 202 (Coma, Brain Compression/Anoxic Damage) under the V28 model, adding a risk factor of about 0.543 for a community, non-dual, aged beneficiary in payment year 2027.

Code Identity

ICD-10-CM Code
R40.2A
Billable Status
Yes — Valid for Submission
Code Describes
Nontraumatic coma due to underlying condition
Short Description
Nontraumatic coma due to underlying condition
Same as the full description in the CMS dataset.
Parent Code
R40.2
Coma

Code Classification

ChapterR00–R99Symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified
SectionR40-R46Symptoms and signs involving cognition, perception, emotional state and behavior
CategoryR40Somnolence, stupor and coma
This CodeR40.2ANontraumatic coma due to underlying condition

Code EditsBilling

Medicare Code Editor checks that affect claim validity for R40.2A.

Unacceptable principal diagnosis
There are selected codes that describe a circumstance which influences an individual's health status but not a current illness or injury, or codes that are not specific manifestations but may be due to an underlying cause. These codes are considered unacceptable as a principal diagnosis.

Medicare Risk Adjustment (HCC)Billing

R40.2A maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2027.

CMS-HCC V28 Category (Payment Model)
HCC 202— Coma, Brain Compression/Anoxic Damage
Payment HCC · PY 2027 one of 61 ICD-10-CM codes in this category
Risk Adjustment Factor (RAF) Weight
+0.543
community, non-dual, aged · ranges 0.097–0.721 across segments
Hierarchy
Superseded by HCC 63, HCC 397, and HCC 398
a more severe related category takes the payment when both are reported
Prior Model (CMS-HCC V24)
HCC 80
V24 retired V28 pays 100% of MA risk scores since PY 2026
Other CMS Models
PACE (CMS-HCC V22): HCC 80 · ESRD (V21): HCC 80 · ESRD (V24): HCC 80
ESRD V21 weights: 0.043 dialysis, 0.000–0.184 functioning graft · ESRD V24 weights: 0.076 dialysis, 0.063–0.679 functioning graft
Part D (RxHCC)
Not mapped
R40.2A does not risk-adjust in the RxHCC prescription drug model

Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to R40.2A: its own notes plus those printed at R40.2, R40, block R40-R46, and Chapter 18. A note printed at a category, block or chapter applies to every code under it.

Applicable To

Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.

  • Secondary coma

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

On R40.2A itself
From R40 Somnolence, stupor and coma applies to 101 codes
  • neonatal coma (P91.5)
  • somnolence, stupor and coma in diabetes (E08-E13)
  • somnolence, stupor and coma in hepatic failure (K72.-)
  • somnolence, stupor and coma in hypoglycemia (nondiabetic) (E15)

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From Block R40-R46 Symptoms and signs involving cognition, perception, emotional state and behavior applies to 157 codes
  • symptoms and signs constituting part of a pattern of mental disorder (F01-F99)
From Chapter 18 (R00-R99) Symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified applies to 774 codes
  • abnormal findings on antenatal screening of mother (O28.-)
  • certain conditions originating in the perinatal period (P04-P96)
  • signs and symptoms classified in the body system chapters
  • signs and symptoms of breast (N63, N64.5)

Code First

The underlying condition named in the note is sequenced before this code.

On R40.2A itself
  • underlying condition
From R40.2 Coma applies to 97 codes
  • any associated:
  • fracture of skull (S02.-)
  • intracranial injury (S06.-)

Notes

General instructions on how these codes are used.

From R40.2 Coma applies to 97 codes
  • One code from each subcategory, R40.21-R40.23, is required to complete the coma scale
From Chapter 18 (R00-R99) Symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified applies to 774 codes
  • This chapter includes symptoms, signs, abnormal results of clinical or other investigative procedures, and ill-defined conditions regarding which no diagnosis classifiable elsewhere is recorded.
  • Signs and symptoms that point rather definitely to a given diagnosis have been assigned to a category in other chapters of the classification. In general, categories in this chapter include the less well-defined conditions and symptoms that, without the necessary study of the case to establish a final diagnosis, point perhaps equally to two or more diseases or to two or more systems of the body. Practically all categories in the chapter could be designated 'not otherwise specified', 'unknown etiology' or 'transient'. The Alphabetical Index should be consulted to determine which symptoms and signs are to be allocated here and which to other chapters. The residual subcategories, numbered .8, are generally provided for other relevant symptoms that cannot be allocated elsewhere in the classification.
  • The conditions and signs or symptoms included in categories R00-R94 consist of:
  • (a) cases for which no more specific diagnosis can be made even after all the facts bearing on the case have been investigated;
  • (b) signs or symptoms existing at the time of initial encounter that proved to be transient and whose causes could not be determined;
  • (c) provisional diagnosis in a patient who failed to return for further investigation or care;
  • (d) cases referred elsewhere for investigation or treatment before the diagnosis was made;
  • (e) cases in which a more precise diagnosis was not available for any other reason;
  • (f) certain symptoms, for which supplementary information is provided, that represent important problems in medical care in their own right.

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name R40.2A, its category, or a range that includes it.

Excludes1 4

These codes carry an Excludes1 note naming R40.2A: they are not reported together with it, unless the two conditions are unrelated.

  • R40.0 Somnolence
    coma (R40.2-) names R40.2-, which includes this code
  • R40.1 Stupor
    coma (R40.2-) names R40.2-, which includes this code
  • R41.82 Altered mental status, unspecified
    altered level of consciousness (R40.-) names R40.-, which includes this code
  • R55 Syncope and collapse
    unconsciousness NOS (R40.2-) names R40.2-, which includes this code

Use Additional Code 2

These codes say to use an additional code from the note, and R40.2A is one of the codes named.

  • T65.85 Toxic effect of medetomidine
    somnolence, stupor and coma (R40.-) names R40.-, which includes this code
  • T67.0 Heatstroke and sunstroke
    coma and stupor (R40.-) names R40.-, which includes this code

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR NVS013
Coma; stupor; and brain damage
Default principal diagnosis: inpatient No · outpatient Yes

Clinical InformationClinical

  • Coma

    a profound state of unconsciousness associated with depressed cerebral activity from which the individual cannot be aroused. coma generally occurs when there is dysfunction or injury involving both cerebral hemispheres or the brain stem reticular formation.

Patient EducationClinical

Coma

A coma is a deep state of unconsciousness. An individual in a coma is alive but unable to move or respond to his or her environment. Coma may occur as a complication of an underlying illness, or as a result of injuries, such as brain injury.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Code History & ChangesHistory

Replacement R40.2A replaces the following previously assigned code(s):

  • R40.20 - Unspecified coma
FY 2024AddedAdded to the ICD-10-CM code setEffective October 1, 2023.
FY 2025–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About R40.2AOverview

What is the ICD-10 code for nontraumatic coma due to underlying condition?

The ICD-10-CM code for nontraumatic coma due to underlying condition is R40.2A (sometimes written as R402A). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is R40.2A (Coma) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report nontraumatic coma due to underlying condition on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does R40.2A group to?

On inpatient claims, nontraumatic coma due to underlying condition maps to MS-DRG 793, 791, 81, 80, with relative weights from 0.7941 to 4.2192 depending on complications. Higher weights mean higher Medicare reimbursement.

Is R40.2A a CC or MCC?

CMS lists R40.2A as an MCC (major complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it places the inpatient stay in the highest-weighted DRG of its severity family. It does not count when the principal diagnosis is one of the 718 closely related codes in its exclusion list.

Can R40.2A be a principal diagnosis?

No. The Medicare Code Editor rejects this code as a principal diagnosis because nontraumatic coma due to underlying condition describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.

What HCC is R40.2A?

R40.2A (nontraumatic coma due to underlying condition) maps to CMS-HCC Category 202 (Coma, Brain Compression/Anoxic Damage), commonly written as HCC 202, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 80 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. It does not map to any RxHCC in the Part D prescription drug model.

Does R40.2A risk-adjust for Medicare Advantage payment?

Yes. When documented and reported on a Medicare Advantage encounter, R40.2A adds a risk adjustment factor of about 0.543 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.097 to 0.721 depending on the payment segment). A more severe related category (HCC 63, HCC 397, and HCC 398) supersedes it when both are reported. See the full factor table on the HCC 202 category page.