2026 ICD-10-CM Diagnosis Code K31.1Adult hypertrophic pyloric stenosis

ICD-10-CM Codes›K00–K95›K20-K31›K31

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

K31.1 is a billable ICD-10-CM diagnosis code for adult hypertrophic pyloric stenosis. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 380 through 382. The code is restricted by the Medicare Code Editor to adult patients (age 15 through 124). 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
K31.1
Billable Status
Yes — Valid for Submission
Code Describes
Adult hypertrophic pyloric stenosis
Short Description
Adult hypertrophic pyloric stenosis
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 CodeK31.1Adult hypertrophic pyloric stenosis

Code EditsBilling

Medicare Code Editor checks that affect claim validity for K31.1.

Adult diagnoses
The Medicare Code Editor detects inconsistencies in adult cases by checking a patient's age and any diagnosis on the patient's record. The adult code edits apply to patients age range is 15–124 years inclusive (e.g., senile delirium, mature cataract).

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Acquired hypertrophic pyloric stenosis
  • Acquired nonhypertrophic constriction of pylorus
  • Acquired obstruction of pylorus
  • Acquired pyloric constriction
  • Acquired pyloric stricture
  • Adult hypertrophic pyloric stenosis
  • Gastric outlet obstruction due to gallstone
  • Peptic ulcer with hemorrhage, with perforation AND with obstruction
  • Pyloric antral stenosis
  • Pyloric obstruction
  • Pyloric stenosis

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • Pyloric stenosis NOS

Type 1 Excludes

  • congenital or infantile pyloric stenosis Q40.0

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.

    • Constriction
      • pylorus (adult hypertrophic)
    • Hypertrophy, hypertrophic
      • pylorus (adult) (muscle) (sphincter)
    • Obstruction, obstructed, obstructive
      • gastric outlet
    • Obstruction, obstructed, obstructive
      • pylorus
        • adult
    • Occlusion, occluded
      • pylorus, adult
    • Stenosis, stenotic(cicatricial)
      • pylorus (hypertrophic) (acquired)
    • Stenosis, stenotic(cicatricial)
      • pylorus (hypertrophic) (acquired)
        • adult
    • Stricture
      • pylorus (hypertrophic)
    • Stricture
      • pylorus (hypertrophic)
        • adult

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

  • Pyloric Stenosis

    narrowing of the pyloric canal with varied etiology. a common form is due to muscle hypertrophy (pyloric stenosis, hypertrophic) seen in infants.

  • Pyloric Stenosis, Hypertrophic

    narrowing of the pyloric canal due to hypertrophy of the surrounding circular muscle. it is usually seen in infants or young children.

  • Hypertrophy

    general increase in bulk of a part or organ due to cell enlargement and accumulation of fluids and secretions, not due to tumor formation, nor to an increase in the number of cells (hyperplasia).

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 K31.1 to ICD-9-CMHistory

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

ICD-9-CM
537.0 Acq pyloric stenosis
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 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About K31.1Overview

Is K31.1 (Other diseases of stomach and duodenum) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report adult hypertrophic pyloric stenosis on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does K31.1 group to?

When adult hypertrophic pyloric stenosis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 380, 381, 382, with relative weights from 0.8006 to 1.9622 depending on complications. Higher weights mean higher Medicare reimbursement.

Who can K31.1 be reported for?

The Medicare Code Editor checks adult hypertrophic pyloric stenosis against patient demographics: this code is intended for adult patients (age 15 through 124). Claims outside these limits are flagged as inconsistent.

What is the ICD-9 equivalent of K31.1?

Under the General Equivalence Mappings, adult hypertrophic pyloric stenosis converts to ICD-9-CM 537.0 (acq pyloric stenosis). The mapping is a direct match.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.