Peritonitis (K65) ICD-10-CM
The K65 code range covers peritonitis with 8 ICD-10-CM diagnosis codes. 7 of them are billable and valid for claim submission in fiscal year 2026, and the category headers group them but cannot themselves be billed.
Code Also
A "code also" note instructs that two codes may be required to fully describe a condition, but this note does not provide sequencing direction.
- if applicable diverticular disease of intestine K57
Use Additional Code
The “use additional code” indicates that a secondary code could be used to further specify the patient’s condition. This note is not mandatory and is only used if enough information is available to assign an additional code.
Type 1 Excludes
A type 1 excludes note is a pure excludes note. It means "NOT CODED HERE!" An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition.
- 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
Codes in the K65 Range 8 codes · 7 billable
Clinical Terms in This Code Range
Definitions from the National Library of Medicine for conditions coded in the K65 range.
Abdominal Abscess
An abscess located in the abdominal cavity, i.e., the cavity between the diaphragm above and the pelvis below. (From Dorland, 27th ed)
Chylous Ascites
Presence of milky lymph (CHYLE) in the PERITONEAL CAVITY, with or without infection.
Coronavirus, Feline
A species of CORONAVIRUS infecting cats of all ages and commonly found in catteries and zoos. Cats are often found carrying the virus but only a small proportion develop disease. Feline coronavirus and Feline infectious peritonitis virus (FIPV) are virtually the same virus in genetic and antigenetic terms, and are morphologically indistinguishable. Since they only differ in their disease potential (with FIPV causing a more serious illness), they are considered biotypes of each other.
Familial Mediterranean Fever
A group of HEREDITARY AUTOINFLAMMATION DISEASES, characterized by recurrent fever, abdominal pain, headache, rash, PLEURISY; and ARTHRITIS. ORCHITIS; benign MENINGITIS; and AMYLOIDOSIS may also occur. Homozygous or compound heterozygous mutations in marenostrin gene encoding PYRIN result in autosomal recessive transmission; simple heterozygous, autosomal dominant form of the disease also exists with mutations in the same gene.
Feline Infectious Peritonitis
Common coronavirus infection of cats caused by the feline infectious peritonitis virus (CORONAVIRUS, FELINE). The disease is characterized by a long incubation period, fever, depression, loss of appetite, wasting, and progressive abdominal enlargement. Infection of cells of the monocyte-macrophage lineage appears to be essential in FIP pathogenesis.
Peritonitis
INFLAMMATION of the PERITONEUM lining the ABDOMINAL CAVITY as the result of infectious, autoimmune, or chemical processes. Primary peritonitis is due to infection of the PERITONEAL CAVITY via hematogenous or lymphatic spread and without intra-abdominal source. Secondary peritonitis arises from the ABDOMINAL CAVITY itself through RUPTURE or ABSCESS of intra-abdominal organs.
Peritonitis, Tuberculous
A form of PERITONITIS seen in patients with TUBERCULOSIS, characterized by lesion either as a miliary form or as a pelvic mass on the peritoneal surfaces. Most patients have ASCITES, abdominal swelling, ABDOMINAL PAIN, and other systemic symptoms such as FEVER; WEIGHT LOSS; and ANEMIA.
Serositis
Inflammation of a serous membrane.
Typhlitis
Necrotizing inflammation of the CECUM (typhlon in Greek), sometimes spreading to the APPENDIX and/or the ILEUM. Symptoms include ABDOMINAL PAIN and DIARRHEA. Its pathogenesis is multifactorial. Typhlitis is often associated with NEUTROPENIA and chemotherapy in immunocompromised individuals (IMMUNOCOMPROMISED HOST).
About the K65 Code Range
The ICD-10 codes in section K65 identify various forms of peritonitis, an inflammation or infection of the peritoneum, the tissue lining the abdominal cavity. These codes specify conditions ranging from generalized acute peritonitis to abscesses and spontaneous bacterial infections.
Commonly referenced as acute infectious peritonitis or purulent peritonitis, K65.0 covers generalized acute peritonitis and related pelvic inflammations. Code K65.1 denotes different types of peritoneal abscesses, including postoperative or retroperitoneal abscesses. K65.2 is used for spontaneous bacterial peritonitis, also known as primary bacterial peritonitis. The code K65.3 addresses choleperitonitis, inflammation due to bile leakage after gallbladder surgery. K65.4 applies to sclerosing mesenteritis, an aseptic fat necrosis of the peritoneum. For less common or other forms of peritonitis, including fungal or parasitic infections and complications from peritoneal dialysis, K65.8 is appropriate. When the type of peritonitis is not specified, K65.9 is used.
Questions About This Page
How many billable codes are in the K65 range?
Of the 8 codes in this range, 7 are billable and valid for claim submission from October 1, 2025 through September 30, 2026. Category header codes group them but cannot be reported on claims.
What does the K65 range classify?
The range classifies peritonitis. Each code links to its own reference page with billing status, MS-DRG grouping, coding notes, and clinical information.
Related References
Source: CMS FY 2026 ICD-10-CM Tabular List and order file, effective October 1, 2025 through September 30, 2026.
