2027 ICD-10-CM Diagnosis Code R63.6Underweight

ICD-10-CM Codes›R00–R99›R50-R69›R63

ICD-10-CM R63.6
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

R63.6 is a billable ICD-10-CM diagnosis code for underweight. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 640 through 641. 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 Other general signs and symptoms.

Code Identity

ICD-10-CM Code
R63.6
Billable Status
Yes — Valid for Submission
Code Describes
Underweight
Short Description
Underweight
Same as the full description in the CMS dataset.
Parent Code
R63
Symptoms and signs concerning food and fluid intake

Code Classification

ChapterR00–R99Symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified
SectionR50-R69General symptoms and signs
CategoryR63Symptoms and signs concerning food and fluid intake
This CodeR63.6Underweight

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Anorexia nervosa co-occurrent with dangerously low body weight
  • Anorexia nervosa co-occurrent with significantly low body weight
  • Anorexia nervosa, binge-eating purging type
  • Anorexia nervosa, restricting type
  • Dangerously low body weight co-occurrent and due to anorexia nervosa of binge-eating purging type
  • Dangerously low body weight co-occurrent and due to anorexia nervosa of restricting type
  • Mild thinness in adulthood
  • Moderate thinness in adulthood
  • Severe thinness in adulthood
  • Significantly low body weight co-occurrent and due to anorexia nervosa of binge-eating purging type
  • Significantly low body weight co-occurrent and due to anorexia nervosa of restricting type
  • Thin build
  • Thin build in adult
  • Underweight
  • Underweight in adolescence
  • Underweight in childhood
  • Underweight in infancy

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to R63.6: its own notes plus those printed at R63 and Chapter 18. A note printed at a category, block or chapter applies to every code under it.

Excludes1

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

On R63.6 itself
From R63 Symptoms and signs concerning food and fluid intake applies to 11 codes

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 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)

Use Additional Code

Add a second code, after this one, to fully describe the condition.

  • code to identify body mass index (BMI), if known (Z68.-)

Notes

General instructions on how these codes are used.

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.

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 SYM016
Other general signs and symptoms
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Body Weight

Body weight is the total mass of your body. Keeping track of your weight is one way to check for changes in your health, but it can't tell you the whole story. That's because your weight includes muscle, bone, fat, and water. Also, everyday factors can play a role in your weight, such as your:

The full article covers:

  • What is body weight?
  • What factors help determine a healthy body weight?
  • What are body weight ranges?
  • What if I have a sudden gain or loss of weight?
  • How can I maintain a healthy body weight?

Read the full article at MedlinePlus

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

Convert R63.6 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
783.22 Underweight
Exact Match The mapping is direct, with no qualifiers.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About R63.6Overview

What is the ICD-10 code for underweight?

The ICD-10-CM code for underweight is R63.6 (sometimes written as R636). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is R63.6 (Symptoms and signs concerning food and fluid intake) a billable code?

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

What MS-DRG does R63.6 group to?

When underweight is the principal diagnosis on an inpatient stay, it groups to MS-DRG 641, 640, with relative weights from 0.7864 to 1.3392 depending on complications. Higher weights mean higher Medicare reimbursement.

Can R63.6 be a principal diagnosis?

Use it with care. This is a symptom code, so once a definitive diagnosis explaining the underweight is established, that condition takes the principal position instead.

Can R63.6 be reported with R63.4?

Not as a rule. The Excludes1 note on R63.6 lists "abnormal weight loss (R63.4)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).