R18.0 ICD-10-CM Code: Malignant ascites

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for R18.0 in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2026Effective: October 1, 2025

Notes without a marker are published on R18.0 itself; “inherited from” names the category or block whose note applies here.

Coder workflow for R18.0

MedCoder structured workflow — derived from this code’s own official record

Before you code R18.0

1. Check whether an established diagnosis that explains this sign or symptom is documented. If one is, review whether the documented diagnosis changes the coding pathway: a symptom that is integral to a confirmed diagnosis is not reported separately, while one not routinely associated with it may be. Signs and symptoms are reported when no definitive diagnosis is established (Guidelines I.B.4, I.B.5, I.B.6, I.C.18.b).

   Guide: Symptom code vs confirmed diagnosis →

2. Check the Excludes1 note: if the documentation supports a condition named there, do not simply proceed with R18.0. Excludes1 conditions are not reported together with this code unless the record shows they are unrelated (Guidelines I.A.12.a).

   See the official tabular notes

Choose the right path

1. Is an established diagnosis that explains this sign or symptom documented?
   Yes → Review whether the documented diagnosis changes the coding pathway: a symptom integral to it is not reported separately.
   No → Continue — the sign or symptom code stands when no definitive diagnosis is established.
2. Does the documentation support a condition named in R18.0’s Excludes1 note?
   Yes → Do not simply proceed: review the excluded code. Both are reported only when the record shows the two conditions are unrelated.
   No → Continue.

   ReviewK70.31, K70.11, K71.51

3. Is the underlying (etiologic) condition the Code First note names documented?
   Yes → Sequence the underlying condition first, then R18.0.
   No → Continue; do not add an underlying condition the record does not document.

   ReviewC56, C78.6

Consider R18.0. Then confirm the code is valid for the date of service in the Verify section.

Documentation check

The provider’s diagnostic statement

Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).

The underlying (etiologic) condition

Named in the Code First note; sequenced before this code when documented (Guidelines I.A.13).

Official instructions as workflow

• Excludes1 — check before selecting R18.0(3 notes)

  Coding workflow: If the documentation supports a condition named in this note, do not simply proceed with R18.0: the two are not reported together. The one exception is when the record shows the two conditions are unrelated to each other.

  CompareK70.31, K70.11, K71.51

  See the official tabular notes · Guidelines I.A.12.a

• Excludes2 — not part of R18.0(9 notes)

  Coding workflow: The conditions named in this note are not included in R18.0. When the record documents both, both may be reported; the note is a boundary, not a prohibition.

  CompareQ40.0, K56, P76, K31.3, N94

  See the official tabular notes · Guidelines I.A.12.b

• Code First — sequencing check(3 notes)

  Coding workflow: Check whether the underlying or etiologic condition the note names is documented. When it is, sequence it before R18.0. Do not add an underlying condition the record does not document.

  ReviewC56, C78.6

  See the official tabular notes · Guidelines I.A.13

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Indexed Clinical Terms (1)

Official source data — entries quoted as published, in the Index’s own lookup phrasing

Clinical term phrases from the official ICD-10-CM Index to Diseases and Injuries that map to this code. These are alphabetic-index entries shown as the Index writes them — lookup phrasing, not necessarily the wording of a final diagnosis.

• Ascites (abdominal), malignant

Don’t confuse R18.0 with…

MedCoder analysis — pairs from this code’s official notes, distinctions written by MedCoder

The codes most likely to be picked instead of R18.0 — named in its own official notes, or sharing its laterality or encounter family — with what separates them and which documentation moves the case. Each links to the full comparison.

• K70.31— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of ascites in alcoholic cirrhosis moves the case to K70.31; the two are not reported together unless documented as unrelated.

  Full comparison: R18.0 vs K70.31 →

• K70.11— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of ascites in alcoholic hepatitis moves the case to K70.11; the two are not reported together unless documented as unrelated.

  Full comparison: R18.0 vs K70.11 →

• K71.51— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of ascites in toxic liver disease with chronic active hepatitis moves the case to K71.51; the two are not reported together unless documented as unrelated.

  Full comparison: R18.0 vs K71.51 →

• Q40.0— Excludes2 relationship (Informational)

  Distinct conditions — both may be reported.

  A distinct condition — both may be reported when both are documented.

  What moves you there: Documentation of congenital or infantile pylorospasm adds Q40.0; it is not part of this code and both may be reported when both are documented.

  Full comparison: R18.0 vs Q40.0 →

• K92.0— Excludes2 relationship (Informational)

  Distinct conditions — both may be reported.

  A distinct condition — both may be reported when both are documented.

  What moves you there: Documentation of gastrointestinal hemorrhage adds K92.0; it is not part of this code and both may be reported when both are documented.

  Full comparison: R18.0 vs K92.0 →

• K92.2— Excludes2 relationship (Informational)

  Distinct conditions — both may be reported.

  A distinct condition — both may be reported when both are documented.

  What moves you there: Documentation of gastrointestinal hemorrhage adds K92.2; it is not part of this code and both may be reported when both are documented.

  Full comparison: R18.0 vs K92.2 →

Relationships are read from this code's own official notes, its laterality siblings and its encounter family; the wording of each distinction is MedCoder editorial, and the documentation named in each “what moves you there” line is the official note phrase or sibling title itself. Source: CMS ICD-10-CM tabular instructional notes; ICD-10-CM Official Guidelines, Section I.A.12.a.

Decision Points

The directives on this code's own record, as a pre-claim checklist.

1. Sequencing: 3 Code First instructions — the underlying condition is sequenced before this code when present. See the Code First notes
2. 3 Excludes1 entries — codes named there are generally not reported together with this code (Guidelines I.A.12.a). See the Excludes1 notes
3. 9 Excludes2 entries — those conditions are not part of this code and may be reported additionally when documented. See the Excludes2 notes

Checklist rows are derived from this code's own official directives; the wording of each check is MedCoder editorial. The official notes themselves are in the sections each row links to.

Verify Before Coding

• Principal-diagnosis restriction. The Medicare Code Editor lists this code as unacceptable as a principal diagnosis: it describes a circumstance influencing health status rather than a current illness or injury being treated. It is valid as a secondary diagnosis.
• CC as a secondary diagnosis (FY2026). Can raise the stay's MS-DRG severity tier.

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder structured relationships — computed from published CMS and AHRQ datasets

Other codes that name R18.0 or its code family, from the CMS ICD-10-CM tabular instructional notes. Tabular-note edges are stored at the code family level that carries each note.

Referenced by 2 Excludes1 notes: R19.0 — Intra-abdominal and pelvic swelling, mass and lump (via R18.-), R60 — Edema, not elsewhere classified (via R18.-).

These codes’ tabular lists mark this diagnosis as mutually exclusive — not reported together unless the conditions are documented as unrelated.

Referenced by 1 Excludes2 note: K66 — Other disorders of peritoneum (via R18.-).

These codes’ tabular lists name this diagnosis as distinct — both may be reported when both are documented.

MS-DRG Grouper Relationships (FY2026)

Potential MS-DRG participation — not a DRG assignment.

FY2026 MS-DRG: CC — Complication or Comorbidity. Reported as a secondary diagnosis, this code raises the stay's MS-DRG severity tier — except when the principal diagnosis is one of 57 clinically related codes on its CMS exclusion list.

Named in the grouper logic of 2 MS-DRGs: DRG 947 (MDC 23), DRG 948 (MDC 23).

From the CMS MS-DRG Definitions Manual (Appendices B and C). Actual DRG assignment depends on the complete claim.

Clinical classification (AHRQ CCSR):NEO074 — Conditions due to neoplasm or the treatment of neoplasm (default); SYM006 — Abdominal pain and other digestive/abdomen signs and symptoms.

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Related Codes

Same clinical process (MS-DRG)

Acts as CC — raises the severity of other admissions. CMS groups these diagnoses into one MS-DRG principal-diagnosis exclusion process — a CC/MCC on this list never raises severity when the principal diagnosis is also on it.

G89.0 — Central pain syndrome, G89.11 — Acute pain due to trauma, G89.12 — Acute post-thoracotomy pain, G89.18 — Other acute postprocedural pain, G89.21 — Chronic pain due to trauma, G89.22 — Chronic post-thoracotomy pain, G89.28 — Other chronic postprocedural pain, G89.29 — Other chronic pain, G89.3 — Neoplasm related pain (acute) (chronic), G89.4 — Chronic pain syndrome, R18.8 — Other ascites, R19.00 — Intra-abdominal and pelvic swelling, mass and lump, unspecified site, R19.01 — Right upper quadrant abdominal swelling, mass and lump, R19.02 — Left upper quadrant abdominal swelling, mass and lump, R19.03 — Right lower quadrant abdominal swelling, mass and lump, R19.04 — Left lower quadrant abdominal swelling, mass and lump, R19.05 — Periumbilic swelling, mass or lump, R19.06 — Epigastric swelling, mass or lump, R19.07 — Generalized intra-abdominal and pelvic swelling, mass and lump, R19.09 — Other intra-abdominal and pelvic swelling, mass and lump, +37 more

Principal diagnosis restriction (Medicare Code Editor)

Not acceptable as a principal diagnosis on an inpatient claim.

Same CMS-HCC risk category (V28)

CMS maps these diagnoses to the same Hierarchical Condition Category (Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic) for risk-adjusted payment.

C92.A1 — Acute myeloid leukemia with multilineage dysplasia, in remission, C92.A2 — Acute myeloid leukemia with multilineage dysplasia, in relapse, C93.00 — Acute monoblastic/monocytic leukemia, not having achieved remission, C93.01 — Acute monoblastic/monocytic leukemia, in remission, C93.02 — Acute monoblastic/monocytic leukemia, in relapse, C94.00 — Acute erythroid leukemia, not having achieved remission, C94.01 — Acute erythroid leukemia, in remission, C94.02 — Acute erythroid leukemia, in relapse, C94.20 — Acute megakaryoblastic leukemia not having achieved remission, C94.21 — Acute megakaryoblastic leukemia, in remission, C94.22 — Acute megakaryoblastic leukemia, in relapse, C94.40 — Acute panmyelosis with myelofibrosis not having achieved remission, C94.41 — Acute panmyelosis with myelofibrosis, in remission, C94.42 — Acute panmyelosis with myelofibrosis, in relapse, D46.22 — Refractory anemia with excess of blasts 2, E34.00 — Carcinoid syndrome, unspecified, E34.01 — Carcinoid heart syndrome, E34.09 — Other carcinoid syndrome, I31.31 — Malignant pericardial effusion in diseases classified elsewhere, J91.0 — Malignant pleural effusion, +57 more

Related risk categories

These categories interact through CMS's HCC hierarchy — one can suppress the other's risk-adjustment weight when both are present on a claim.

Cancer Metastatic to Bone, Other and Unspecified Metastatic Cancer; Acute Leukemia Except Myeloid, Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers, Lung and Other Severe Cancers, Lymphoma and Other Cancers, Bladder, Colorectal, and Other Cancers, Prostate, Breast, and Other Cancers and Tumors

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical categories (Conditions due to neoplasm or the treatment of neoplasm, Abdominal pain and other digestive/abdomen signs and symptoms).

R14.2 — Eructation, R14.3 — Flatulence, R15.0 — Incomplete defecation, R15.1 — Fecal smearing, R15.2 — Fecal urgency, R15.9 — Full incontinence of feces, R16.0 — Hepatomegaly, not elsewhere classified, R16.1 — Splenomegaly, not elsewhere classified, R16.2 — Hepatomegaly with splenomegaly, not elsewhere classified, R17 — Unspecified jaundice, R18.8 — Other ascites, R19.00 — Intra-abdominal and pelvic swelling, mass and lump, unspecified site, R19.01 — Right upper quadrant abdominal swelling, mass and lump, R19.02 — Left upper quadrant abdominal swelling, mass and lump, R19.03 — Right lower quadrant abdominal swelling, mass and lump, R19.04 — Left lower quadrant abdominal swelling, mass and lump, R19.05 — Periumbilic swelling, mass or lump, R19.06 — Epigastric swelling, mass or lump, R19.07 — Generalized intra-abdominal and pelvic swelling, mass and lump, R19.09 — Other intra-abdominal and pelvic swelling, mass and lump, +114 more

Same Index main term, other category

The ICD-10-CM Index to Diseases and Injuries files this code under the main term “Ascites”; these codes share that main term but sit in a different category of the Tabular List.

A18.31 — Tuberculous peritonitis (tuberculous), A52.74 — Syphilis of liver and other viscera (syphilitic), B65.2 — Schistosomiasis due to Schistosoma japonicum (due to, S. japonicum), I50.810 — Right heart failure, unspecified (heart), I89.8 — Other specified noninfective disorders of lymphatic vessels and lymph nodes (chylous), K70.11 — Alcoholic hepatitis with ascites (due to, hepatitis, alcoholic), K70.31 — Alcoholic cirrhosis of liver with ascites (due to, cirrhosis, alcoholic), K71.51 — Toxic liver disease with chronic active hepatitis with ascites (due to, hepatitis, chronic active, with toxic liver disease), K73.2 — Chronic active hepatitis, not elsewhere classified (due to, hepatitis, chronic active)

Lab tests where this diagnosis supports Medicare coverage (NCD)

Medicare's National Coverage Determination (NCD) program lists this diagnosis as medical justification for these lab tests.

Fecal Occult Blood Test (FOBT), Prothrombin Time Test and INR (PT/INR), Thyroid Stimulating Hormone (TSH)

Contextual Map

Every relationship of R18.0 in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run R18.0 with these 5 related codes in Claim Check

Hierarchy

• R00-R99 — Chapter 18: Symptoms, Signs and Abnormal Clinical and Laboratory Findings, Not Elsewhere Classified (R00-R99) (R00-R99)[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• R10-R19 — Symptoms and signs involving the digestive system and abdomen[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026

Code First

• C56 — Malignant neoplasm of ovary[Code First]: “malignant neoplasm of ovary (C56.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
• C78.6 — Secondary malignant neoplasm of retroperitoneum and peritoneum[Code First]: “secondary malignant neoplasm of retroperitoneum and peritoneum (C78.6)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Referenced by Excludes1 notes

• R19.0 — Intra-abdominal and pelvic swelling, mass and lump[Excludes1](via R18.-): “ascites (R18.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
• R60 — Edema, not elsewhere classified[Excludes1](via R18.-): “ascites (R18.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Referenced by Excludes2 notes

• K66 — Other disorders of peritoneum[Excludes2](via R18.-): “ascites (R18.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Clinical classification (CCSR)

• NEO074 — Conditions due to neoplasm or the treatment of neoplasm[CCSR]— AHRQ CCSR for ICD-10-CM Diagnoses (HCUP)
• SYM006 — Abdominal pain and other digestive/abdomen signs and symptoms[CCSR]— AHRQ CCSR for ICD-10-CM Diagnoses (HCUP)

Risk adjustment (CMS-HCC)

• HCC 17 — Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic [CMS-HCC]: “Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic — supersedes HCC 18 (Cancer Metastatic to Bone, Other and Unspecified Metastatic Cancer; Acute Leukemia Except Myeloid), HCC 19 (Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers), HCC 20 (Lung and Other Severe Cancers), HCC 21 (Lymphoma and Other Cancers), HCC 22 (Bladder, Colorectal, and Other Cancers), HCC 23 (Prostate, Breast, and Other Cancers and Tumors)”— CMS-HCC V28 · 2026

MS-DRG Grouper

• CC — Complication or Comorbidity [MS-DRG severity]: “As a secondary diagnosis this code can raise the stay's MS-DRG severity tier (CC).”— CMS MS-DRG Definitions Manual (Appendix C) · FY2026
• DRG 947 — SIGNS AND SYMPTOMS WITH MCC[MS-DRG]: “SIGNS AND SYMPTOMS WITH MCC (MDC 23)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 948 — SIGNS AND SYMPTOMS WITHOUT MCC[MS-DRG]: “SIGNS AND SYMPTOMS WITHOUT MCC (MDC 23)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026

MDC crossing

• MDC 23 — Factors Influencing Health Status and Other Contacts with Health Services[MDC crossing]: “Factors Influencing Health Status and Other Contacts with Health Services — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs. 1,235 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2026

Index entries

• Ascites (abdominal), malignant[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026

Nearest codes

• R18 — Ascites[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• R18.8 — Other ascites[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026

Change history

• FY2016 — In the code set at ICD-10-CM adoption [Change history]— CMS release files (code change ledger) · icd10cm-fy2016

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data

CMS/CDC ICD-10-CM FY2026 tabular list, index and tables, effective October 1, 2025 Release, file and checksum · Publisher’s page

Claim edits Official source data

CMS Definitions of Medicare Code Edits — v43.1 (April 2026) Release, file and checksum · Publisher’s page

Inpatient payment groups Official source data

CMS MS-DRG Definitions Manual (incl. Appendix B diagnosis index, Appendix C CC/MCC list, Appendix E procedure index) and IPPS Final Rule tables — v43 Release, file and checksum · Publisher’s page

Risk adjustment Official source data

2026 Mid-Year Final ICD-10 Mappings + Model Software (cms.gov/files/zip/2026-midyear-final-icd-10-mappings.zip, 2026-midyear-final-model-software.zip) — CMS-HCC V28, PY2026 mid-year final release Release, file and checksum · Publisher’s page

Change history and date-of-service validity Official source data

CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page

Comparisons, relationships and the contextual map MedCoder structured relationship

Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears

Summary and FAQ answers MedCoder explanation

Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates

Nearest Codes in This Family

Official ICD-10-CM classifications closest to R18.0 in its code family, with their registry titles.

• R18 — Ascites
• R18.8 — Other ascites

View all codes in the R18 family