2026 ICD-10-CM Diagnosis Code R63.6Underweight
ICD-10-CM Codes›R00–R99›R50-R69›R63
- Billable — Valid for Submission
- Not Chronic
R63.6 is a billable ICD-10-CM diagnosis code for underweight. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) 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
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Anorexia nervosa
- 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
Tabular List NotesGuidance
Coding notes and annotation back-references applicable to this code.
Use Additional Code
- code to identify body mass index BMI, if known Z68
Type 1 Excludes
The “use additional code” indicates that a secondary code could be used to further specify the patient’s condition. This note is not mandatory and is only used if enough information is available to assign an additional code.
A type 1 excludes note is a pure excludes note. It means "NOT CODED HERE!" An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
- Underweight - R63.6
External Cause of Injuries IndexGuidance
References for this code in the External Cause of Injuries Index.
- Underweight
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Anorexia Nervosa
an eating disorder that is characterized by the lack or loss of appetite, known as anorexia. other features include excess fear of becoming overweight; body image disturbance; significant weight loss; refusal to maintain minimal normal weight; and amenorrhea. this disorder occurs most frequently in adolescent females. (apa, thesaurus of psychological index terms, 1994)
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.
Code HistoryHistory
Questions About R63.6Overview
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, 2025 through September 30, 2026.
What MS-DRG does R63.6 group to?
When underweight is the principal diagnosis on an inpatient stay, it groups to MS-DRG 640, 641, with relative weights from 0.7782 to 1.3356 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.
What is the ICD-9 equivalent of R63.6?
Under the General Equivalence Mappings, underweight converts to ICD-9-CM 783.22 (underweight). The mapping is a direct match.
Footnotes
[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.
