2027 ICD-10-CM Diagnosis Code K65.8Other peritonitis

ICD-10-CM Codes›K00–K95›K65-K6A›K65

ICD-10-CM K65.8
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

K65.8 is a billable ICD-10-CM diagnosis code for other peritonitis. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 371 through 373, 791, 793. As a secondary diagnosis, it counts as a major complication or comorbidity (MCC) and places an inpatient stay in the highest severity level of its MS-DRG family. It does not count, however, when the principal diagnosis is one of 25 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Peritonitis and intra-abdominal abscess.

For Medicare Advantage risk adjustment, K65.8 maps to CMS-HCC Category 78 (Intestinal Obstruction/Perforation) under the V28 model, adding a risk factor of about 0.326 for a community, non-dual, aged beneficiary in payment year 2027.

Code Identity

ICD-10-CM Code
K65.8
Billable Status
Yes — Valid for Submission
Code Describes
Other peritonitis
Short Description
Other peritonitis
Same as the full description in the CMS dataset.
Parent Code
K65
Peritonitis

Code Classification

ChapterK00–K95Diseases of the digestive system
SectionK65-K6ADiseases of peritoneum and retroperitoneum
CategoryK65Peritonitis
This CodeK65.8Other peritonitis

Medicare Risk Adjustment (HCC)Billing

K65.8 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2027.

CMS-HCC V28 Category (Payment Model)
HCC 78— Intestinal Obstruction/Perforation
Payment HCC · PY 2027 one of 76 ICD-10-CM codes in this category
Risk Adjustment Factor (RAF) Weight
+0.326
community, non-dual, aged · ranges 0.326–0.688 across segments
Hierarchy
Superseded by HCC 77
a more severe related category takes the payment when both are reported
Prior Model (CMS-HCC V24)
HCC 33
V24 retired V28 pays 100% of MA risk scores since PY 2026
Other CMS Models
PACE (CMS-HCC V22): HCC 33 · ESRD (V21): HCC 33 · ESRD (V24): HCC 33
ESRD V21 weights: 0.072 dialysis, 0.285–0.346 functioning graft · ESRD V24 weights: 0.078 dialysis, 0.250–0.474 functioning graft
Part D (RxHCC)
Not mapped
K65.8 does not risk-adjust in the RxHCC prescription drug model

Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Acute cecitis
  • Acute cecitis with perforation AND peritonitis
  • Acute polyserositis
  • Acute serositis
  • Chronic peritonitis
  • Chronic polyserositis
  • Chronic proliferative peritonitis
  • Continuous ambulatory peritoneal dialysis associated peritonitis
  • Eosinophilia of peritoneal fluid
  • Eosinophilic peritonitis
  • Fat necrosis of peritoneum
  • Fecal peritonitis
  • Fungal peritonitis
  • Granulomatous peritonitis
  • Infection associated with peritoneal dialysis catheter
  • Injury of cecum
  • Long-term disorder of dialysis
  • Mesenteric fat necrosis
  • Mesenteric fat saponification
  • Parasitic peritonitis
  • Perforation of cecum
  • Perihepatitis
  • Peritoneal dialysis-associated peritonitis
  • Peritoneal fluid abnormal
  • Peritonitis due to infected peritoneal dialysis catheter
  • Polyserositis
  • Polyserositis syndrome of dialysis
  • Serositis
  • Typhlitis
  • Urine peritonitis

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to K65.8: its own notes plus those printed at K65 and Chapter 11. A note printed at a category, block or chapter applies to every code under it.

Applicable To

Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.

  • Chronic proliferative peritonitis
  • Peritonitis due to urine

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

From K65 Peritonitis applies to 7 codes
  • 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.-)

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From Chapter 11 (K00-K95) Diseases of the digestive system applies to 863 codes
  • certain conditions originating in the perinatal period (P04-P96)
  • certain infectious and parasitic diseases (A00-B99)
  • complications of pregnancy, childbirth and the puerperium (O00-O9A)
  • congenital malformations, deformations and chromosomal abnormalities (Q00-Q99)
  • endocrine, nutritional and metabolic diseases (E00-E88)
  • injury, poisoning and certain other consequences of external causes (S00-T88)
  • neoplasms (C00-D49)
  • symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)

Use Additional Code

Add a second code, after this one, to fully describe the condition.

From K65 Peritonitis applies to 7 codes
  • code (B95-B97), to identify infectious agent, if known

Code Also

A second code may be needed to fully describe the condition; the note gives no sequencing direction.

From K65 Peritonitis applies to 7 codes
  • if applicable diverticular disease of intestine (K57.-)

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name K65.8, its category, or a range that includes it.

Code Also 1

These codes say K65.8 may also be needed to fully describe the condition. The note gives no sequencing direction.

  • K57 Diverticular disease of intestine
    peritonitis (K65.-) names K65.-, which includes this code

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

Clinical ClassificationClinical

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

CCSR DIG016
Peritonitis and intra-abdominal abscess
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Serositis

    inflammation of a serous membrane.

Patient EducationClinical

Peritoneal Disorders

Your peritoneum is the tissue that lines your abdominal wall and covers most of the organs in your abdomen. A liquid, peritoneal fluid, lubricates the surface of this tissue.

Read the full article at MedlinePlus

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

Convert K65.8 to ICD-9-CMHistory

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

ICD-9-CM
567.89 Peritonitis NEC
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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About K65.8Overview

What is the ICD-10 code for other peritonitis?

The ICD-10-CM code for other peritonitis is K65.8 (sometimes written as K658). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is K65.8 (Peritonitis) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report other peritonitis on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does K65.8 group to?

When other peritonitis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 372, 793, 791, 371, 373, with relative weights from 0.6945 to 4.2192 depending on complications. Higher weights mean higher Medicare reimbursement.

Is K65.8 a CC or MCC?

CMS lists K65.8 as an MCC (major complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it places the inpatient stay in the highest-weighted DRG of its severity family. It does not count when the principal diagnosis is one of the 25 closely related codes in its exclusion list.

Can K65.8 be reported with a code from K35.2?

Not as a rule. The Excludes1 note at K65, which applies to K65.8, lists "acute appendicitis with generalized peritonitis (K35.2-)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).

What HCC is K65.8?

K65.8 (other peritonitis) maps to CMS-HCC Category 78 (Intestinal Obstruction/Perforation), commonly written as HCC 78, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 33 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. It does not map to any RxHCC in the Part D prescription drug model.

Does K65.8 risk-adjust for Medicare Advantage payment?

Yes. When documented and reported on a Medicare Advantage encounter, K65.8 adds a risk adjustment factor of about 0.326 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.326 to 0.688 depending on the payment segment). A more severe related category (HCC 77) supersedes it when both are reported. See the full factor table on the HCC 78 category page.