2026 ICD-10-CM Diagnosis Code I31.31Malignant pericardial effusion in diseases classified elsewhere
ICD-10-CM Codes›I00–I99›I30-I5A›I31
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Risk Adjusts — HCC 17
- Chronic Condition
I31.31 is a billable ICD-10-CM diagnosis code for malignant pericardial effusion in diseases classified elsewhere. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 314 through 316. 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 17 closely related codes. The code is a manifestation code that cannot be reported as the principal diagnosis. Coders also document this condition as malignant neoplasm of pericardium. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Pericarditis and pericardial disease.
For Medicare Advantage risk adjustment, I31.31 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 2026.
Code Identity
Code Classification
Code EditsBilling
Medicare Code Editor checks that affect claim validity for I31.31.
Medicare Risk Adjustment (HCC)Billing
I31.31 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 2026.
Source: CMS Payment Year 2026 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.
- Malignant neoplasm of pericardium
- Malignant pericardial effusion
- Pericardial effusion co-occurrent and due to malignant neoplasm of pericardium
Tabular List NotesGuidance
Coding notes and annotation back-references applicable to this code.
Code First
Certain conditions have both an underlying etiology and multiple body system manifestations due to the underlying etiology. For such conditions, the ICD-10-CM has a coding convention that requires the underlying condition be sequenced first followed by the manifestation. Wherever such a combination exists, there is a "use additional code" note at the etiology code, and a "code first" note at the manifestation code. These instructional notes indicate the proper sequencing order of the codes, etiology followed by manifestation.
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.
Clinical InformationClinical
Malignant Pericardial Effusion
presence of fluid in the pericardial space as a complication of malignant disease.
Patient EducationClinical
Cardiopulmonary Syndromes (PDQ®)
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Code History & ChangesHistory
Replacement I31.31 replaces the following previously assigned code(s):
- I31.3 - Pericardial effusion (noninflammatory)
Questions About I31.31Overview
What is the ICD-10 code for malignant pericardial effusion in diseases classified elsewhere?
The ICD-10-CM code for malignant pericardial effusion in diseases classified elsewhere is I31.31 (sometimes written as I3131). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
Is I31.31 (Pericardial effusion (noninflammatory)) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report malignant pericardial effusion in diseases classified elsewhere on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does I31.31 group to?
On inpatient claims, malignant pericardial effusion in diseases classified elsewhere maps to MS-DRG 314, 315, 316, with relative weights from 0.6821 to 2.0852 depending on complications. Higher weights mean higher Medicare reimbursement.
Is I31.31 a CC or MCC?
CMS lists I31.31 as a CC (complication or comorbidity) for FY 2026. 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 17 closely related codes in its exclusion list.
Can I31.31 be a principal diagnosis?
No. This is a manifestation code: malignant pericardial effusion in diseases classified elsewhere describes the manifestation of an underlying disease rather than the disease itself, so the underlying condition is sequenced first.
What HCC is I31.31?
I31.31 (malignant pericardial effusion in diseases classified elsewhere) 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 2026. It does not map to any RxHCC in the Part D prescription drug model.
Does I31.31 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, I31.31 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.
