ICD-10-CM 2027
ICD-10 code for Serositis
From the official ICD-10-CM alphabetic index entry “Serositis, multiple”. Page updated September 29, 2026.
About coding Serositis
The ICD-10-CM code for Serositis is K65.8 (Other peritonitis). The official index lists 2 more specific codes, so check the documentation for details such as type, cause, site or severity before settling on K65.8.
Within K65, choose K65.8 (Other peritonitis) only when documentation doesn't support a more specific option: generalized (acute) peritonitis (K65.0), peritoneal abscess (K65.1), spontaneous bacterial peritonitis (K65.2), Choleperitonitis (K65.3), sclerosing mesenteritis (K65.4) and unspecified (K65.9).
Use an additional code (B95-B97), to identify infectious agent, if known.
As a secondary diagnosis it is an MCC (major complication or comorbidity), which can move an inpatient stay into the highest-paying "with MCC" MS-DRG of its family, unless the principal diagnosis excludes it.
More specific Serositis codes (official index)
Common questions about Serositis ICD-10 codes
What is the ICD-10 code for Serositis?
- K65.8 — Other peritonitis. More specific codes apply when the documentation supports them: I31.1, K65.8.
What is the ICD-10 code for pericardial serositis?
- I31.1 — Chronic constrictive pericarditis.
What is the ICD-10 code for peritoneal serositis?
- K65.8 — Other peritonitis.
Is K65.8 billable?
- Yes. K65.8 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).
Can K65.8 be used as a principal diagnosis?
- Yes. The Medicare Code Editor doesn't restrict K65.8 as a principal diagnosis.
Is K65.8 a CC or MCC?
- K65.8 is an MCC (major complication or comorbidity) under MS-DRG v44.0, unless excluded by the principal diagnosis.