2026 ICD-10-CM Diagnosis Code K31.9Disease of stomach and duodenum, unspecified

ICD-10-CM Codes›K00–K95›K20-K31›K31

ICD-10-CM K31.9
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

K31.9 is a billable ICD-10-CM diagnosis code for disease of stomach and duodenum, unspecified. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 391 through 392. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified and unspecified disorders of stomach and duodenum.

Code Identity

ICD-10-CM Code
K31.9
Billable Status
Yes — Valid for Submission
Code Describes
Disease of stomach and duodenum, unspecified
Short Description
Disease of stomach and duodenum, unspecified
Same as the full description in the CMS dataset.
Parent Code
K31
Other diseases of stomach and duodenum

Code Classification

ChapterK00–K95Diseases of the digestive system
SectionK20-K31Diseases of esophagus, stomach and duodenum
CategoryK31Other diseases of stomach and duodenum
This CodeK31.9Disease of stomach and duodenum, unspecified

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Disorder of duodenum
  • Disorder of stomach
  • Erosive duodenopathy
  • Erosive gastropathy
  • Gastric dysplasia
  • Gastric mucosal lesion
  • Gastritis medicamentosa
  • Gastroduodenal disorder
  • Hypertrophic gastropathy
  • Lesion of stomach
  • Mild stomach dysplasia
  • Moderate stomach dysplasia
  • NSAID-associated gastropathy
  • Papulous gastropathy
  • Reactive gastropathy
  • Severe stomach dysplasia
  • Stomach problem

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Disease, diseased
      • duodenum
    • Disease, diseased
      • stomach
    • Disorder(of)
      • gastric (functional)
    • Disturbance(s)
      • stomach (functional)
    • Dysfunction
      • pylorus
    • Gastropathy
    • Lesion(s) (nontraumatic)
      • cardia
    • Lesion(s) (nontraumatic)
      • duodenum
    • Lesion(s) (nontraumatic)
      • gastric
    • Lesion(s) (nontraumatic)
      • gastroduodenal
    • Lesion(s) (nontraumatic)
      • pylorus
    • Lesion(s) (nontraumatic)
      • stomach

Clinical ClassificationClinical

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

CCSR DIG008
Other specified and unspecified disorders of stomach and duodenum
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Gastric Dysplasia

    a morphologic finding indicating the presence of dysplastic changes within the gastric mucosal epithelial cells.

  • Indefinite for Gastric Dysplasia|Indefinite for Gastric Intraepithelial Neoplasia

    a term used to describe an ambiguous morphologic pattern in the gastric mucosa, when there is doubt whether the findings represent a non-neoplastic or neoplastic pathologic process.

  • Negative for Gastric Dysplasia|Negative for Gastric Intraepithelial Neoplasia

    a morphologic finding indicating the absence of dysplastic changes in the gastric mucosal epithelium. it includes non-neoplastic inflammatory, reactive, or metaplastic pathologic processes.

Patient EducationClinical

Stomach Disorders

Your stomach is an organ between your esophagus and small intestine. It is where digestion of protein begins. The stomach has three tasks. It stores swallowed food. It mixes the food with stomach acids. Then it sends the mixture on to the small intestine.

Read the full article at MedlinePlus

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

Convert K31.9 to ICD-9-CMHistory

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

ICD-9-CM
536.9 Stomach function dis NOS
Approximate The match is approximate rather than exact.
ICD-9-CM
537.9 Gastroduodenal dis NOS
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About K31.9Overview

Is K31.9 (Other diseases of stomach and duodenum) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report disease of stomach and duodenum, unspecified on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does K31.9 group to?

When disease of stomach and duodenum, unspecified is the principal diagnosis on an inpatient stay, it groups to MS-DRG 391, 392, with relative weights from 0.7796 to 1.2683 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of K31.9?

Under the General Equivalence Mappings, disease of stomach and duodenum, unspecified converts to ICD-9-CM 536.9 (stomach function dis NOS) and 537.9 (gastroduodenal dis NOS). The mapping is approximate, so confirm the match fits the documentation.

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.