2027 ICD-10-CM Diagnosis Code R18.0Malignant ascites

ICD-10-CM Codes›R00–R99›R10-R19›R18

ICD-10-CM R18.0
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

R18.0 is a billable ICD-10-CM diagnosis code for malignant ascites. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 947 through 948. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 57 closely related codes. The code is not accepted as a principal diagnosis by the Medicare Code Editor. As a symptom code, it should not be used as a principal diagnosis once a related definitive diagnosis has been established. Coders also document this condition as ascitic fluid examination abnormal. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Abdominal pain and other digestive/abdomen signs and symptoms and Conditions due to neoplasm or the treatment of neoplasm.

For Medicare Advantage risk adjustment, R18.0 maps to CMS-HCC Category 17 (Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic) under the V28 model, adding a risk factor of about 4.209 for a community, non-dual, aged beneficiary in payment year 2027.

Code Identity

ICD-10-CM Code
R18.0
Billable Status
Yes — Valid for Submission
Code Describes
Malignant ascites
Short Description
Malignant ascites
Same as the full description in the CMS dataset.
Parent Code
R18
Ascites

Code Classification

ChapterR00–R99Symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified
SectionR10-R19Symptoms and signs involving the digestive system and abdomen
CategoryR18Ascites
This CodeR18.0Malignant ascites

Code EditsBilling

Medicare Code Editor checks that affect claim validity for R18.0.

Unacceptable principal diagnosis
There are selected codes that describe a circumstance which influences an individual's health status but not a current illness or injury, or codes that are not specific manifestations but may be due to an underlying cause. These codes are considered unacceptable as a principal diagnosis.

Medicare Risk Adjustment (HCC)Billing

R18.0 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 17— Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic
Payment HCC · PY 2027 one of 78 ICD-10-CM codes in this category
Risk Adjustment Factor (RAF) Weight
+4.209
community, non-dual, aged · ranges 1.952–4.235 across segments
Hierarchy
Supersedes HCC 18, HCC 19, HCC 20, HCC 21, HCC 22, and HCC 23
less severe related categories are not paid alongside HCC 17
Prior Model (CMS-HCC V24)
Not mapped under V24
this diagnosis newly risk-adjusts under the V28 model
Part D (RxHCC)
Not mapped
R18.0 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.

  • Ascitic fluid examination abnormal
  • Ascitic fluid: malignant cells
  • Malignant ascites
  • Peritoneal fluid abnormal

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to R18.0: its own notes plus those printed at R18, block R10-R19, and Chapter 18. A note printed at a category, block or chapter applies to every code under it.

Includes

Further defines, or gives examples of, the content of the category.

From R18 Ascites applies to 2 codes
  • fluid in peritoneal cavity

Excludes1

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

From R18 Ascites applies to 2 codes
  • ascites in alcoholic cirrhosis (K70.31)
  • ascites in alcoholic hepatitis (K70.11)
  • ascites in toxic liver disease with chronic active hepatitis (K71.51)

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 Block R10-R19 Symptoms and signs involving the digestive system and abdomen applies to 99 codes
  • congenital or infantile pylorospasm (Q40.0)
  • gastrointestinal hemorrhage (K92.0-K92.2)
  • intestinal obstruction (K56.-)
  • newborn gastrointestinal hemorrhage (P54.0-P54.3)
  • newborn intestinal obstruction (P76.-)
  • pylorospasm (K31.3)
  • signs and symptoms involving the urinary system (R30-R39)
  • symptoms referable to female genital organs (N94.-)
  • symptoms referable to male genital organs (N48-N50)
From Chapter 18 (R00-R99) Symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified applies to 774 codes
  • abnormal findings on antenatal screening of mother (O28.-)
  • certain conditions originating in the perinatal period (P04-P96)
  • signs and symptoms classified in the body system chapters
  • signs and symptoms of breast (N63, N64.5)

Code First

The underlying condition named in the note is sequenced before this code.

  • malignancy, such as:
  • malignant neoplasm of ovary (C56.-)
  • secondary malignant neoplasm of retroperitoneum and peritoneum (C78.6)

Notes

General instructions on how these codes are used.

From Chapter 18 (R00-R99) Symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified applies to 774 codes
  • This chapter includes symptoms, signs, abnormal results of clinical or other investigative procedures, and ill-defined conditions regarding which no diagnosis classifiable elsewhere is recorded.
  • Signs and symptoms that point rather definitely to a given diagnosis have been assigned to a category in other chapters of the classification. In general, categories in this chapter include the less well-defined conditions and symptoms that, without the necessary study of the case to establish a final diagnosis, point perhaps equally to two or more diseases or to two or more systems of the body. Practically all categories in the chapter could be designated 'not otherwise specified', 'unknown etiology' or 'transient'. The Alphabetical Index should be consulted to determine which symptoms and signs are to be allocated here and which to other chapters. The residual subcategories, numbered .8, are generally provided for other relevant symptoms that cannot be allocated elsewhere in the classification.
  • The conditions and signs or symptoms included in categories R00-R94 consist of:
  • (a) cases for which no more specific diagnosis can be made even after all the facts bearing on the case have been investigated;
  • (b) signs or symptoms existing at the time of initial encounter that proved to be transient and whose causes could not be determined;
  • (c) provisional diagnosis in a patient who failed to return for further investigation or care;
  • (d) cases referred elsewhere for investigation or treatment before the diagnosis was made;
  • (e) cases in which a more precise diagnosis was not available for any other reason;
  • (f) certain symptoms, for which supplementary information is provided, that represent important problems in medical care in their own right.

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

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name R18.0, its category, or a range that includes it.

Excludes1 2

These codes carry an Excludes1 note naming R18.0: they are not reported together with it, unless the two conditions are unrelated.

  • R19.0 Intra-abdominal and pelvic swelling, mass and lump
    ascites (R18.-) names R18.-, which includes this code
  • R60 Edema, not elsewhere classified
    ascites (R18.-) names R18.-, which includes this code

Excludes2 1

These codes carry an Excludes2 note naming R18.0: its condition is not part of those codes, and both may be reported when the patient has both.

  • K66 Other disorders of peritoneum
    ascites (R18.-) names R18.-, 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 SYM006
Abdominal pain and other digestive/abdomen signs and symptoms
Default principal diagnosis: inpatient No · outpatient No
CCSR NEO074
Conditions due to neoplasm or the treatment of neoplasm
Default principal diagnosis: inpatient No · outpatient Yes

Clinical InformationClinical

  • Malignant Ascites

    accumulation of fluid in the peritoneal cavity resulting from the growth of primary or metastatic malignant neoplasms in the peritoneum.

  • Ascites

    accumulation or retention of free fluid within the peritoneal cavity.

Patient EducationClinical

Liver Diseases

Your liver is the largest organ inside your body. It helps your body digest food, store energy, and remove poisons.

Read the full article at MedlinePlus

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

Convert R18.0 to ICD-9-CMHistory

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

ICD-9-CM
789.51 Malignant ascites
Exact Match The mapping is direct, with no qualifiers.

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 R18.0Overview

What is the ICD-10 code for malignant ascites?

The ICD-10-CM code for malignant ascites is R18.0 (sometimes written as R180). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is R18.0 (Ascites) a billable code?

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

What MS-DRG does R18.0 group to?

On inpatient claims, malignant ascites maps to MS-DRG 948, 947, with relative weights from 0.7833 to 1.2608 depending on complications. Higher weights mean higher Medicare reimbursement.

Is R18.0 a CC or MCC?

CMS lists R18.0 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 57 closely related codes in its exclusion list.

Can R18.0 be a principal diagnosis?

No. The Medicare Code Editor rejects this code as a principal diagnosis because malignant ascites describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.

What HCC is R18.0?

R18.0 (malignant ascites) maps to CMS-HCC Category 17 (Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic), commonly written as HCC 17, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It does not map to any RxHCC in the Part D prescription drug model.

Does R18.0 risk-adjust for Medicare Advantage payment?

Yes. When documented and reported on a Medicare Advantage encounter, R18.0 adds a risk adjustment factor of about 4.209 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 1.952 to 4.235 depending on the payment segment). HCC 17 sits at the top of its hierarchy, so no other condition category supersedes it. See the full factor table on the HCC 17 category page.