Ascites (R18) ICD-10-CM
The R18 code range covers ascites with 3 ICD-10-CM diagnosis codes. 2 of them are billable and valid for claim submission in fiscal year 2026, and the category headers group them but cannot themselves be billed.
Includes
This note appears immediately under a three character code title to further define, or give examples of, the content of the category.
- fluid in peritoneal cavity
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.
Codes in the R18 Range 3 codes · 2 billable
Clinical Terms in This Code Range
Definitions from the National Library of Medicine for conditions coded in the R18 range.
Ascites
Accumulation or retention of free fluid within the peritoneal cavity.
Carcinoma, Ehrlich Tumor
A transplantable, poorly differentiated malignant tumor which appeared originally as a spontaneous breast carcinoma in a mouse. It grows in both solid and ascitic forms.
Chylous Ascites
Presence of milky lymph (CHYLE) in the PERITONEAL CAVITY, with or without infection.
Mucin-4
A transmembrane mucin that is found in a broad variety of epithelial tissue. Mucin-4 may play a role in regulating cellular adhesion and in cell surface signaling from the ERBB-2 RECEPTOR PROTEIN-TYROSINE KINASE. Mucin-4 is a heterodimer of alpha and beta chains. The alpha and beta chains result from the proteolytic cleavage of a precursor protein.
Peritoneovenous Shunt
An operation for the continuous emptying of ascitic fluid into the venous system. Fluid removal is based on intraperitoneal and intrathoracic superior vena cava pressure differentials and is performed via a pressure-sensitive one-way valve connected to a tube traversing the subcutaneous tissue of the chest wall to the neck where it enters the internal jugular vein and terminates in the superior vena cava. It is used in the treatment of intractable ascites.
Pseudomyxoma Peritonei
A peritoneal adenocarcinoma characterized by build-up of MUCUS in the PERITONEAL CAVITY. Mucus secreting cells may attach to the peritoneal lining and continue to secrete mucus. The majority of cases represent tumor spread from a primary low-grade mucinous neoplasm of the APPENDIX (NCI Thesaurus).
Receptor, ErbB-2
A cell surface protein-tyrosine kinase receptor that is overexpressed in a variety of ADENOCARCINOMAS. It has extensive homology to and heterodimerizes with the EGF RECEPTOR, the ERBB-3 RECEPTOR, and the ERBB-4 RECEPTOR. Activation of the erbB-2 receptor occurs through heterodimer formation with a ligand-bound erbB receptor family member.
About the R18 Code Range
ICD-10 code R18 is used to classify ascites, a condition characterized by excess fluid buildup in the abdomen. It includes specific codes for different types of ascites based on the underlying cause, such as malignant or other forms.
The general code R18 represents ascites without further specification. For cases involving cancer-related fluid accumulation, R18.0 describes malignant ascites, identified by abnormal or malignant cells found in the peritoneal fluid. This code helps distinguish ascites caused by tumors or cancer treatment. The code R18.8 covers other ascites types, including those linked to dialysis, bile leakage, infections, metabolic causes, or complications like pancreatic ascites. It also includes terms such as hepatic ascites, hemorrhagic ascites, and refractory ascites. Coders and healthcare providers utilize these codes to document specific ascites conditions accurately in clinical records, enabling clear differentiation of causes like cancer, infection, or biochemical imbalances. Using the ICD-10 code for ascites correctly supports precise diagnosis and tailored medical management.
Questions About This Page
How many billable codes are in the R18 range?
Of the 3 codes in this range, 2 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 R18 range classify?
The range classifies ascites. 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.
