2027 ICD-10-CM Diagnosis Code H70.91Unspecified mastoiditis, right ear

ICD-10-CM Codes›H60–H95›H65-H75›H70

ICD-10-CM H70.91
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

H70.91 is a billable ICD-10-CM diagnosis code for unspecified mastoiditis, right ear. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 152 through 153. Coders also document this condition as abscess of mastoid. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Diseases of middle ear and mastoid (except otitis media).

Code Identity

ICD-10-CM Code
H70.91
Billable Status
Yes — Valid for Submission
Code Describes
Unspecified mastoiditis, right ear
Short Description
Unspecified mastoiditis, right ear
Same as the full description in the CMS dataset.
Parent Code
H70.9
Unspecified mastoiditis

Code Classification

ChapterH60–H95Diseases of the ear and mastoid process
SectionH65-H75Diseases of middle ear and mastoid
CategoryH70Mastoiditis and related conditions
This CodeH70.91Unspecified mastoiditis, right ear

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Abscess of mastoid
  • Abscess of right mastoid
  • Abscess of temporal bone
  • Right mastoiditis

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to H70.91: its own notes plus those printed at Chapter 8. A note printed at a category, block or chapter applies to every code under it.

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 Chapter 8 (H60-H95) Diseases of the ear and mastoid process applies to 653 codes
  • certain conditions originating in the perinatal period (P04-P96)
  • certain infectious and parasitic diseases (A00-B99)
  • complications of pregnancy, childbirth and the puerperium (O00-O9A)
  • congenital malformations, deformations and chromosomal abnormalities (Q00-Q99)
  • endocrine, nutritional and metabolic diseases (E00-E88)
  • injury, poisoning and certain other consequences of external causes (S00-T88)
  • neoplasms (C00-D49)
  • symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)

Notes

General instructions on how these codes are used.

From Chapter 8 (H60-H95) Diseases of the ear and mastoid process applies to 653 codes
  • Use an external cause code following the code for the ear condition, if applicable, to identify the cause of the ear condition

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

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name H70.91, its category, or a range that includes it.

Excludes2 1

These codes carry an Excludes2 note naming H70.91: its condition is not part of those codes, and both may be reported when the patient has both.

  • H74 Other disorders of middle ear mastoid
    mastoiditis (H70.-) names H70.-, which includes this code

Clinical ClassificationClinical

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

CCSR EAR002
Diseases of middle ear and mastoid (except otitis media)
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Mastoiditis

    inflammation of the honeycomb-like mastoid bone in the skull just behind the ear. it is usually a complication of otitis media.

Patient EducationClinical

Ear Infections

Ear infections are the most common reason parents bring their child to a doctor. Three out of four children will have at least one ear infection by their third birthday. Adults can also get ear infections, but they are less common.

Read the full article at MedlinePlus

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

Convert H70.91 to ICD-9-CMHistory

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

ICD-9-CM
383.9 Mastoiditis NOS
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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About H70.91Overview

What is the ICD-10 code for unspecified mastoiditis, right ear?

The ICD-10-CM code for unspecified mastoiditis, right ear is H70.91 (sometimes written as H7091). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is H70.91 (Unspecified mastoiditis) a billable code?

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

What MS-DRG does H70.91 group to?

When unspecified mastoiditis, right ear is the principal diagnosis on an inpatient stay, it groups to MS-DRG 152, 153, with relative weights from 0.7420 to 1.1147 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of H70.91?

Under the General Equivalence Mappings, unspecified mastoiditis, right ear converts to ICD-9-CM 383.9 (mastoiditis NOS). The mapping is approximate, so confirm the match fits the documentation.