2026 ICD-10-CM Diagnosis Code B51.9Plasmodium vivax malaria without complication

ICD-10-CM Codes›A00–B99›B50-B64›B51

ICD-10-CM B51.9
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

B51.9 is a billable ICD-10-CM diagnosis code for plasmodium vivax malaria without complication. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 867 through 869. Coders also document this condition as intermittent fever. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Parasitic, other specified and unspecified infections.

Code Identity

ICD-10-CM Code
B51.9
Billable Status
Yes — Valid for Submission
Code Describes
Plasmodium vivax malaria without complication
Short Description
Plasmodium vivax malaria without complication
Same as the full description in the CMS dataset.
Parent Code
B51
Plasmodium vivax malaria

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionB50-B64Protozoal diseases
CategoryB51Plasmodium vivax malaria
This CodeB51.9Plasmodium vivax malaria without complication

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Intermittent fever
  • Malarial fever
  • Tertian fever
  • Vivax malaria

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • Plasmodium vivax malaria NOS

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Malaria, malarial(fever)
      • Plasmodium (P.)
        • vivax NEC
    • Malaria, malarial(fever)
      • vivax

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR INF009
Parasitic, other specified and unspecified infections
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Vivax Malaria

    malaria resulting from infection by plasmodium vivax.

Patient EducationClinical

Malaria

Malaria is a serious disease caused by a parasite. You get it when an infected mosquito bites you. Malaria is a major cause of death worldwide, but it is almost wiped out in the United States. The disease is mostly a problem in developing countries with warm climates. If you travel to these countries, you are at risk.

Read the full article at MedlinePlus

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

Convert B51.9 to ICD-9-CMHistory

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

ICD-9-CM
084.1 Vivax malaria
Approximate The match is approximate rather than exact.
ICD-9-CM
084.5 Mixed malaria
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About B51.9Overview

Is B51.9 (Plasmodium vivax malaria) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report plasmodium vivax malaria without complication on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does B51.9 group to?

When plasmodium vivax malaria without complication is the principal diagnosis on an inpatient stay, it groups to MS-DRG 867, 868, 869, with relative weights from 0.7297 to 2.0932 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of B51.9?

Under the General Equivalence Mappings, plasmodium vivax malaria without complication converts to ICD-9-CM 084.1 (vivax malaria) and 084.5 (mixed malaria). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.