What is ICD-10 code I79.1?

I79.1 is the ICD-10-CM diagnosis code for Aortitis in diseases classified elsewhere. It belongs to the ICD-10-CM chapter for diseases of the circulatory system (i00-i99). I79.1 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. I79.1 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. I79.1 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. I79.1 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

Which HCC does I79.1 map to under V28?

I79.1 does not map to a CMS-HCC V28 payment category. Check the current CMS-HCC V28 model file for payment year 2026 rather than an older V24 tip sheet.

What does I79.1 pay in RAF?

I79.1 has no separately stated V28 community RAF weight. If it is not a V28 payment HCC, it adds nothing to a community RAF score.

What is the V28 vs V24 difference for I79.1?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. I79.1 was a payment HCC under V24 (Vascular Disease) but the V28 recalibration removed it from the risk adjustment model. Both models can still appear in legacy data and in payer-specific lookback periods.

What documentation supports I79.1?

This is a combination code that requires documentation of the underlying disease causing the aortitis; always code the primary disease first, then use I79.1 as a secondary diagnosis Common underlying causes include syphilis, tuberculosis, rheumatoid arthritis, and other systemic inflammatory conditions; ensure the causal relationship is clearly documented in the medical record Because I79.1 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score. See the MEAT criteria checklist at /meat-criteria for what Monitor, Evaluate, Assess, or Treat looks like in a note. MEAT is generic documentation evidence, not a payer-specific rule.

2026 ICD-10-CM I79.1: Aortitis in diseases

I79.1 is not a CMS-HCC payment code. MEAT criteria · RAF calculator · HCC coding software

ICD-10-CM Code View

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Code lookupI79.1Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Diseases of the circulatory system (I00-I99) / Diseases of arteries, arterioles and capillaries (I70-I79)

I79.1

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Aortitis in diseases classified elsewhere

This code describes inflammation of the aorta (the body's largest blood vessel) that occurs as a complication of another disease listed elsewhere in the medical record. The aortitis is a secondary condition caused by an underlying disease rather than a primary condition.

Buddy Insight

Aortitis in diseases classified elsewhere represents inflammation of the aortic wall secondary to an underlying systemic disease such as syphilis, rheumatoid arthritis, or giant cell arteritis.

CMS-HCC V28

N/A

—

Not risk-adjusted for this model/period.

Not mapped

CMS-HCC V24

Mapped

HCC 108

Vascular Disease

RAF 0.288

ACA/HHS

N/A

—

Not risk-adjusted for this model/period.

Not mapped

ESRD/PACE

Mapped

HCC 108

Vascular Disease

RAF 0.073

RXHCC

N/A

—

Not risk-adjusted for this model/period.

Not mapped

Code Book Path

Official

I79Disorders of arteries, arterioles and capillaries in diseases classified elsewhere

I79.1Aortitis in diseases classified elsewhere

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for I79.1 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for I79.1 in this effective period.

Related Child Codes

Official

I79.0Aneurysm of aorta in diseases classified elsewhere

I79.8Other disorders of arteries, arterioles and capillaries in diseases classified elsewhere

Includes

Official

ICD-10-CM does not list Includes notes for I79.1 in this effective period.

Excludes 1

Official

syphilitic aortitis (A52.02)

Code First

Official

underlying disease

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for I79.1 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for I79.1 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Documentation of aortic wall inflammation with supporting imaging or laboratory evidence

Identification of the underlying causative disease (must be coded first)

Imaging demonstrating aortitis (CT, magnetic resonance imaging, or positron emission tomography showing aortic wall thickening or enhancement)

Assessment for complications including aneurysm formation or stenosis

MEAT Support

HCC Buddy guidance

Documentation of aortic wall inflammation with supporting imaging or laboratory evidence

Identification of the underlying causative disease (must be coded first)

Imaging demonstrating aortitis (CT, magnetic resonance imaging, or positron emission tomography showing aortic wall thickening or enhancement)

Assessment for complications including aneurysm formation or stenosis

Audit Caution

HCC Buddy guidance

Using this code without sequencing the underlying disease code first

Confusing with primary aortitis conditions like Takayasu arteritis which have their own codes

Not recognizing this as a manifestation code that cannot stand alone

Failing to distinguish between aortitis (inflammation) and aortic aneurysm (dilation)

Common Mistakes

HCC Buddy guidance

I77.6 — Arteritis, unspecified: use for non-aortic arteritis or when etiology is primary

I79.0 — Aneurysm of aorta in diseases classified elsewhere: when aneurysm has formed, not just inflammation

M31.4 — Aortic arch syndrome (Takayasu): primary arteritis with its own code

A52.02 — Syphilitic aortitis: use as the primary code with I79.1 as manifestation

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is I79.1 an HCC code?

Yes. I79.1 maps to Vascular Disease under the V24 model but is not retained in V28.

Code: I79.1
Description: Aortitis in diseases classified elsewhere
HCC (V28): No CMS-HCC V28 mapping
RAF: —
Billable: Yes
Payment year: 2026

HCC Category Mapping

V24HCC 108, Vascular Disease

0.288

ESRDHCC 108, Vascular Disease

0.073

Each model's RAF is its CMS base weight for that model's standard population, so weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.

Work I79.1 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for I79.1

For I79.1 to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.

MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
EEvaluate: test results, medication response, or physical findings reviewed by the provider
AAssess: explicit mention in the assessment or plan with acknowledgment of status
TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed I79.1 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

I79.1 is the ICD-10-CM diagnosis code for aortitis in diseases classified elsewhere. This code describes inflammation of the aorta (the body's largest blood vessel) that occurs as a complication of another disease listed elsewhere in the medical record. The aortitis is a secondary condition caused by an underlying disease rather than a primary condition. I79.1 sits in the ICD-10-CM chapter for diseases of the circulatory system (i00-i99), within the section covering diseases of arteries, arterioles and capillaries (i70-i79).

Under the older CMS-HCC V24 model, I79.1 maps to Vascular Disease (HCC 108) with a community, non-dual, aged base RAF weight of 0.288. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.

This is a combination code that requires documentation of the underlying disease causing the aortitis; always code the primary disease first, then use I79.1 as a secondary diagnosis. Because I79.1 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.

HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for I79.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•This is a combination code that requires documentation of the underlying disease causing the aortitis; always code the primary disease first, then use I79.1 as a secondary diagnosis
•Common underlying causes include syphilis, tuberculosis, rheumatoid arthritis, and other systemic inflammatory conditions; ensure the causal relationship is clearly documented in the medical record

Clinical Significance

Aortitis in diseases classified elsewhere represents inflammation of the aortic wall secondary to an underlying systemic disease such as syphilis, rheumatoid arthritis, or giant cell arteritis. This is a manifestation code requiring sequencing of the primary etiology first. Aortitis can weaken the aortic wall and lead to aneurysm or dissection, making it a clinically significant finding requiring ongoing monitoring.

Documentation Requirements

✓Documentation of aortic wall inflammation with supporting imaging or laboratory evidence
✓Identification of the underlying causative disease (must be coded first)
✓Imaging demonstrating aortitis (CT, magnetic resonance imaging, or positron emission tomography showing aortic wall thickening or enhancement)
✓Assessment for complications including aneurysm formation or stenosis
✓Treatment of the underlying inflammatory condition
✓Surveillance plan for aortic complications

Excludes 1, Do NOT code together

syphilitic aortitis (A52.02)

Code First

underlying disease

Commonly Confused Codes

•I77.6: Arteritis, unspecified: use for non-aortic arteritis or when etiology is primary
•I79.0: Aneurysm of aorta in diseases classified elsewhere: when aneurysm has formed, not just inflammation
•M31.4: Aortic arch syndrome (Takayasu): primary arteritis with its own code
•A52.02: Syphilitic aortitis: use as the primary code with I79.1 as manifestation

Child Codes

I79.0Aneurysm of aorta in diseases classified elsewhere

I79.1Aortitis in diseases classified elsewhere

I79.8Other disorders of arteries, arterioles and capillaries in diseases classified elsewhere

Code Hierarchy

└I79Disorders of arteries, arterioles and capillaries in diseases classified elsewhere └I79.1Aortitis in diseases classified elsewhere

└I79.1Aortitis in diseases classified elsewhere

I79.1 ICD-10-CM Code: Aortitis in diseases classified elsewhere

HCC Buddy Code Card

I79.1

Is I79.1 an HCC code?

HCC Category Mapping

MEAT Criteria for I79.1

Get the V28 RAF + MEAT cheat sheet

What This Code Means

Coding Tips

Clinical Significance

Documentation Requirements

Excludes 1, Do NOT code together

Code First

Commonly Confused Codes

Child Codes

Code Hierarchy

Work I79.1 in HCC Buddy