2026 ICD-10-CM Diagnosis Code S31.659AOpen bite of abdominal wall, unspecified quadrant with penetration into peritoneal cavity, initial encounter

ICD-10-CM Codes›S00–T88›S30-S39›S31

ICD-10-CM S31.659A
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

S31.659A is a billable ICD-10-CM diagnosis code for open bite of abdominal wall, unspecified quadrant with penetration into peritoneal cavity, initial encounter. The 7th character A marks it as an initial encounter code, used while the patient is receiving active treatment. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 393 through 395, 963 through 965. The code is flagged as an unspecified code, since codes identifying laterality exist in the same family. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Open wounds of trunk, initial encounter.

Code Identity

ICD-10-CM Code
S31.659A
Billable Status
Yes — Valid for Submission
Code Describes
Open bite of abdominal wall, unspecified quadrant with penetration into peritoneal cavity, initial encounter
Short Description
Open bite of abd wall, unsp quadrant w penet perit cav, init
Parent Code
S31.659
Open bite of abdominal wall, unspecified quadrant with penetration into peritoneal cavity

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionS30-S39Injuries to the abdomen, lower back, lumbar spine, pelvis and external genitals
CategoryS31Open wound of abdomen, lower back, pelvis and external genitals
This CodeS31.659AOpen bite of abdominal wall, unspecified quadrant with penetration into peritoneal cavity, initial encounter

Code EditsBilling

Medicare Code Editor checks that affect claim validity for S31.659A.

Unspecified codes
Unspecified codes exist in the ICD-10-CM classification for circumstances when documentation in the medical record does not provide the level of detail needed to support reporting a more specific code. However, in the inpatient setting, there should generally be very limited and rare circumstances for which the laterality (right, left, bilateral) of a condition is unable to be documented and reported. The following pages contain the list of unspecified ICD-10-CM diagnosis codes for which there is a more specific code to identify laterality (right, left, bilateral) within that code family.

Coding GuidelinesGuidance

The appropriate 7th character is to be added to each code from block Open wound of abdomen, lower back, pelvis and external genitals (S31). Use the following options for the applicable episode of care:

  • A - initial encounter
  • D - subsequent encounter
  • S - sequela

Source: ICD-10-CM Official Guidelines for Coding and Reporting, FY 2026, published by CMS and the National Center for Health Statistics.

Clinical ClassificationClinical

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

CCSR INJ013
Open wounds of trunk, initial encounter
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

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Read the full article at MedlinePlus

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

Convert S31.659A to ICD-9-CMHistory

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

ICD-9-CM
868.13 Peritoneum injury-open
Approximate The match is approximate rather than exact.

Code History & ChangesHistory

Replaced This code was replaced in the FY 2026 code set by:

  • S31.656A - Open bite of abd wall, r flank with penet perit cav, init
  • S31.656A - Open bite of abd wall, r flank with penet perit cav, init
  • S31.657A - Open bite of abd wall, left flank with penet perit cav, init
  • S31.657A - Open bite of abd wall, left flank with penet perit cav, init
  • S31.65AA - Open bite of abd wall, unsp flank with penet perit cav, init
  • S31.65AA - Open bite of abd wall, unsp flank with penet perit cav, init
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 S31.659AOverview

Is S31.659A a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report open bite of abdominal wall, unspecified quadrant with penetration into peritoneal cavity, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character A in S31.659A mean?

The final character A marks the initial encounter: use it while the patient is receiving active treatment for open bite of abdominal wall, unspecified quadrant with penetration into peritoneal cavity, such as an emergency visit or first evaluation.

What MS-DRG does S31.659A group to?

When open bite of abdominal wall, unspecified quadrant with penetration into peritoneal cavity, initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 393, 394, 395, 963, 964, 965, with relative weights from 0.6490 to 2.7338 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of S31.659A?

Under the General Equivalence Mappings, open bite of abdominal wall, unspecified quadrant with penetration into peritoneal cavity, initial encounter converts to ICD-9-CM 868.13 (peritoneum injury-open). 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.