Skip to main content
Call AIBook a demo

ICD-10-CM K65.9: Peritonitis, unspecified

K65.9 is the billable ICD-10-CM code for peritonitis, unspecified, in category K65 (Peritonitis) of the Diseases of peritoneum, retroperitoneum and pelvis section. As a principal diagnosis it groups to MS-DRG 371 Major Gastrointestinal Disorders and Peritoneal Infections with MCC, MS-DRG 372 Major Gastrointestinal Disorders and Peritoneal Infections with CC, MS-DRG 373 Major Gastrointestinal Disorders and Peritoneal Infections without CC/MCC (MDC 06 MDC 06: Diseases and Disorders of the Digestive System); or MS-DRG 791 Prematurity with Major Problems, MS-DRG 793 Full Term Neonate with Major Problems (MDC 15 MDC 15: Newborns and Other Neonates with Conditions Originating in Perinatal Period). It maps to HCC 78 (Intestinal Obstruction/Perforation) in CMS-HCC V28. As a secondary diagnosis it is an MCC, excluded with 25 principal diagnoses. 2 LCD billing and coding articles list it as covered.

Compiled from CMS files by the QuickIntell RCM Editorial Team · Data effective · Method: reference methodology · Report a data correction

Data currency: ICD-10-CM code descriptions: FY2027 (effective October 1, 2026); IPPS Table 5 (MS-DRG weights): v44 FY2027 (final rule + CN3) (effective October 1, 2026); ICD-10-CM to HCC mapping: PY2027 initial ICD-10-CM mappings (dates of service 2026) (payment year 2027); Medicare Coverage Database billing and coding articles: MCD release October 8, 2026 (effective October 4, 2026). Next CMS release: FY2028 code files, effective October 1, 2027 for the ICD-10-CM code descriptions; FY2028 final rule (August 2027), effective October 1, 2027; an April 1 interim grouper update when CMS issues one for the IPPS Table 5 (MS-DRG weights); PY2028 advance notice (February 2027) and the PY2027 midyear final mapping (spring 2027) for the ICD-10-CM to HCC mapping; weekly, every Thursday for the Medicare Coverage Database billing and coding articles.

Code
K65.9
billable FY2027 ICD-10-CM code
Category
K65 Peritonitis
Chapter
11: Diseases of the digestive system (K00-K95)
CC/MCC (MS-DRG v44)
MCC
CMS-HCC V28
HCC 78
POA reporting
Required

Tabular list notes for K65.9

The tabular list has no notes on K65.9 itself; the notes below apply from its parent headings.

Inherited from K65 (Peritonitis)

Excludes1 (never coded together)
  • acute appendicitis with generalized peritonitis (K35.2-)
  • aseptic peritonitis (T81.6)
  • benign paroxysmal peritonitis (E85.0)
  • chemical peritonitis (T81.6)
  • gonococcal peritonitis (A54.85)
  • neonatal peritonitis (P78.0-P78.1)
  • pelvic peritonitis, female (N73.3-N73.5)
  • periodic familial peritonitis (E85.0)
  • peritonitis due to talc or other foreign substance (T81.6)
  • peritonitis in chlamydia (A74.81)
  • peritonitis in diphtheria (A36.89)
  • peritonitis in syphilis (late) (A52.74)
  • peritonitis in tuberculosis (A18.31)
  • peritonitis with or following abortion or ectopic or molar pregnancy (O00-O07, O08.0)
  • peritonitis with or following appendicitis (K35.-)
  • puerperal peritonitis (O85)
  • retroperitoneal infections (K68.-)
Use additional code
  • code (B95-B97), to identify infectious agent, if known
Code also
  • if applicable diverticular disease of intestine (K57.-)

MS-DRG grouping when K65.9 is the principal diagnosis

MS-DRG v44 groups for K65.9 as principal diagnosis
MDCMS-DRGs
06 MDC 06: Diseases and Disorders of the Digestive System371372373
15 MDC 15: Newborns and Other Neonates with Conditions Originating in Perinatal Period791793

The final group also depends on procedures, secondary diagnoses and discharge status; the MS-DRG lookup for K65.9 shows the full grouping logic.

CC/MCC status and inpatient edits

As a secondary diagnosis, K65.9 is an MCC under MS-DRG v44, unless the principal diagnosis is one of the 25 codes in its exclusion list. Check K65.9 against a principal diagnosis.

  • Present on admission: a POA indicator is required on inpatient claims.

CMS-HCC V28 risk adjustment

In the PY2027 mapping, K65.9 maps to HCC 78 (Intestinal Obstruction/Perforation). The HCC lookup shows the RAF weight and the hierarchy.

LCD billing and coding articles that list K65.9

2 current Medicare billing and coding articles list K65.9 among the diagnoses that support medical necessity for the services they cover.

For teams evaluating QuickIntell software

Evaluate software for diagnosis coding review

If your team codes diagnoses at volume, review how QuickCode supports qualified coder review of documentation, specificity queries and the billing handoff. Confirm the code sets, settings and reviewer responsibilities during evaluation; a code reference is not a coding determination for a patient.

Evaluate QuickCode for diagnosis codingSee risk adjustment review
Book a software demoAsk about a software workflow

Optional software evaluation, not payer support or help with an individual claim. For coverage or payment decisions, use the official sources on this page. Do not include patient information in a demo booking or inquiry.

Frequently asked questions

What does ICD-10-CM K65.9 mean?

K65.9 means peritonitis, unspecified. It is one of 7 billable codes under K65, peritonitis.

What can't be coded with K65.9?

Excludes1 at K65: acute appendicitis with generalized peritonitis (K35.2-); aseptic peritonitis (T81.6); benign paroxysmal peritonitis (E85.0); chemical peritonitis (T81.6) and 13 more. These are never reported together with K65.9.

Which MS-DRG does K65.9 group to?

As the principal diagnosis, K65.9 groups to MS-DRG 371 Major Gastrointestinal Disorders and Peritoneal Infections with MCC, MS-DRG 372 Major Gastrointestinal Disorders and Peritoneal Infections with CC, MS-DRG 373 Major Gastrointestinal Disorders and Peritoneal Infections without CC/MCC (MDC 06 MDC 06: Diseases and Disorders of the Digestive System); or MS-DRG 791 Prematurity with Major Problems, MS-DRG 793 Full Term Neonate with Major Problems (MDC 15 MDC 15: Newborns and Other Neonates with Conditions Originating in Perinatal Period) under MS-DRG v44, before procedures and secondary diagnoses are applied.

Does K65.9 map to an HCC?

Yes: HCC 78, Intestinal Obstruction/Perforation, in the PY2027 CMS-HCC V28 mapping.

Is K65.9 a CC or MCC?

K65.9 is an MCC under MS-DRG v44; 25 principal diagnoses exclude it.

Sources

Every figure on this page is taken from the CMS publications below, as released by the Centers for Medicare & Medicaid Services. Projection built 2026-10-10. Verify against the primary file before billing or contracting decisions. The reference methodology explains how each figure is computed from these files.

Disclaimer

The descriptor and notes are reproduced from the FY2027 ICD-10-CM files; MS-DRG, CC/MCC and HCC facts come from the CMS FY2027 and PY2027 tables. Code from the medical record and the ICD-10-CM Official Guidelines. Not legal, clinical or billing advice.

Found a figure that does not match the CMS file? Report a data correction with the CMS file and the value you expected; the request reaches the editorial team through the contact form.