2026 ICD-10-CM Diagnosis Code I42.1Obstructive hypertrophic cardiomyopathy
ICD-10-CM Codes›I00–I99›I30-I5A›I42
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Risk Adjusts — HCC 227
- Chronic Condition
I42.1 is a billable ICD-10-CM diagnosis code for obstructive hypertrophic cardiomyopathy. 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 112 closely related codes. Coders also document this condition as hypertrophic obstructive cardiomyopathy. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Myocarditis and cardiomyopathy.
For Medicare Advantage risk adjustment, I42.1 maps to CMS-HCC Category 227 (Cardiomyopathy/Myocarditis) under the V28 model, adding a risk factor of about 0.189 for a community, non-dual, aged beneficiary in payment year 2026.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
I42.1 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.
- Hypertrophic obstructive cardiomyopathy
Tabular List NotesGuidance
Coding notes and annotation back-references applicable to this code.
Inclusion Terms
- Hypertrophic subaortic stenosis (idiopathic)
These terms are the conditions for which that code is to be used. The terms may be synonyms of the code title, or, in the case of "other specified" codes, the terms are a list of the various conditions assigned to that code. The inclusion terms are not necessarily exhaustive. Additional terms found only in the Alphabetic Index may also be assigned to a code.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
Myocardiopathy (congestive) (constrictive) (familial) (hypertrophic nonobstructive) (idiopathic) (infiltrative) (obstructive) (primary) (restrictive) (sporadic) See Also: Cardiomyopathy; I42.9
hypertrophic obstructive I42.1
Stenosis, stenotic (cicatricial) See Also: Stricture;
myocardium, myocardial See Also: Degeneration, myocardial;
Stricture See Also: Stenosis;
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Patient EducationClinical
Cardiomyopathy
Cardiomyopathy is the name for diseases of the heart muscle. These diseases enlarge your heart muscle or make it thicker and more rigid than normal. In rare cases, scar tissue replaces the muscle tissue.
Read the full article at MedlinePlus
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Convert I42.1 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About I42.1Overview
What is the ICD-10 code for obstructive hypertrophic cardiomyopathy?
The ICD-10-CM code for obstructive hypertrophic cardiomyopathy is I42.1 (sometimes written as I421). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
Is I42.1 (Cardiomyopathy) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report obstructive hypertrophic cardiomyopathy on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does I42.1 group to?
When obstructive hypertrophic cardiomyopathy is the principal diagnosis on an inpatient stay, it groups 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 I42.1 a CC or MCC?
CMS lists I42.1 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 112 closely related codes in its exclusion list.
What is the ICD-9 equivalent of I42.1?
Under the General Equivalence Mappings, obstructive hypertrophic cardiomyopathy converts to ICD-9-CM 425.11 (hyprtrophc obst cardiomy). The mapping is a direct match.
What HCC is I42.1?
I42.1 (obstructive hypertrophic cardiomyopathy) maps to CMS-HCC Category 227 (Cardiomyopathy/Myocarditis), commonly written as HCC 227, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2026. It mapped to HCC 85 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. In the Part D prescription drug model it maps to RxHCC 186.
Does I42.1 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, I42.1 adds a risk adjustment factor of about 0.189 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.145 to 0.200 depending on the payment segment). A more severe related category (HCC 221, HCC 222, HCC 223, HCC 224, HCC 225, and HCC 226) supersedes it when both are reported. See the full factor table on the HCC 227 category page.
