What is ICD-10 code E00.1?

E00.1 is the ICD-10-CM diagnosis code for Congenital iodine-deficiency syndrome, myxedematous type. It belongs to the ICD-10-CM chapter for endocrine, nutritional and metabolic diseases (e00-e89). E00.1 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. E00.1 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. E00.1 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. E00.1 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.

What is the V28 vs V24 difference for E00.1?

E00.1 does not map to a payment HCC under either the CMS-HCC V28 risk adjustment model or the older V24 model. V28 reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition. Because neither community model rewards E00.1 with a risk adjustment factor, it contributes zero to a Medicare Advantage beneficiary's V28/V24 community RAF score in either version. It does, however, map under the Part D RxHCC model (Thyroid and Parathyroid Disorders), which affects the ESRD and/or Part D (RxHCC) risk scores. Coders should check whether provider documentation supports a more specific child code that does map to a community payment HCC.

What should coders know when reporting E00.1?

This code is rarely used in modern developed countries due to iodine supplementation programs; verify documentation clearly states congenital iodine-deficiency syndrome with myxedematous manifestations before coding Do not confuse with acquired hypothyroidism (E03.x) or other congenital thyroid disorders; ensure the iodine deficiency etiology is explicitly documented

2026 ICD-10-CM E00.1: Congenital iodine-deficiency syndrome

ICD-10-CM Code View

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Code lookupE00.1Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Endocrine, nutritional and metabolic diseases (E00-E89) / Disorders of thyroid gland (E00-E07)

E00.1

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

Congenital iodine-deficiency syndrome, myxedematous type

This is a rare congenital condition where a baby is born with severe thyroid hormone deficiency due to lack of iodine during pregnancy, resulting in intellectual disability, growth problems, and characteristic facial puffiness. It represents the most severe form of iodine deficiency disease affecting newborns.

Buddy Insight

CMS-HCC V28

N/A

—

Not risk-adjusted for this model/period.

Not mapped

CMS-HCC V24

N/A

—

Not risk-adjusted for this model/period.

Not mapped

ACA/HHS

N/A

—

Not risk-adjusted for this model/period.

Not mapped

ESRD/PACE

N/A

—

Not risk-adjusted for this model/period.

Not mapped

RXHCC

Mapped

HCC 44

Thyroid and Parathyroid Disor...

RAF 0.070

Code Book Path

Official

E00Congenital iodine-deficiency syndrome

E00.1Congenital iodine-deficiency syndrome, myxedematous type

Inclusion Terms

Official

Endemic hypothyroid cretinism
Endemic cretinism, myxedematous type

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for E00.1 in this effective period.

Related Child Codes

Official

E00.0Congenital iodine-deficiency syndrome, neurological type

E00.2Congenital iodine-deficiency syndrome, mixed type

E00.9Congenital iodine-deficiency syndrome, unspecified

Includes

Official

ICD-10-CM does not list Includes notes for E00.1 in this effective period.

Excludes 1

Official

subclinical iodine-deficiency hypothyroidism (E02)

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for E00.1 in this effective period.

Use Additional

Official

code (F70-F79) to identify associated intellectual disabilities.

Code Also

Official

ICD-10-CM does not list Code Also instructions for E00.1 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Documentation must confirm the myxedematous type of congenital iodine-deficiency syndrome with hypothyroid clinical features (growth retardation, myxedema, delayed bone age), thyroid function tests showing severe hypothyroidism, and history consistent with iodine deficiency.

The myxedematous type should be distinguished from the neurological type based on the predominant clinical features.

Thyroid replacement therapy and response should be documented.

MEAT Support

HCC Buddy guidance

The myxedematous type should be distinguished from the neurological type based on the predominant clinical features.

Thyroid replacement therapy and response should be documented.

Audit Caution

HCC Buddy guidance

Do not assign this code for acquired hypothyroidism or hypothyroidism from causes other than iodine deficiency.

The myxedematous type specifically requires evidence of prenatal/postnatal iodine deficiency as the etiology.

This condition is exceedingly rare in regions with iodine supplementation.

Ensure thyroid replacement therapy is documented when prescribed.

Common Mistakes

HCC Buddy guidance

E00.0 (Neurological type) presents primarily with neurological damage rather than hypothyroid features.

E03.0 (Congenital hypothyroidism with diffuse goiter) and E03.1 (Congenital hypothyroidism without goiter) capture hypothyroidism from non-iodine-deficiency causes.

E03.9 (Hypothyroidism, unspecified) lacks the specificity of congenital iodine-deficiency etiology.

Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.

Is E00.1 an HCC code?

E00.1 is not in the CMS-HCC V28 or V24 community payment model, but it does map to Thyroid and Parathyroid Disorders under the Part D RxHCC model.

Code: E00.1
Description: Congenital iodine-deficiency syndrome, myxedematous type
HCC (V28): No CMS-HCC V28 mapping
RAF: —
Billable: Yes
Payment year: 2026

HCC Category Mapping

RxHCCHCC 44, Thyroid and Parathyroid Disorders

0.070

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 E00.1 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for E00.1

For E00.1to 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 E00.1 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

E00.1 is the ICD-10-CM diagnosis code for congenital iodine-deficiency syndrome, myxedematous type. This is a rare congenital condition where a baby is born with severe thyroid hormone deficiency due to lack of iodine during pregnancy, resulting in intellectual disability, growth problems, and characteristic facial puffiness. It represents the most severe form of iodine deficiency disease affecting newborns. E00.1 sits in the ICD-10-CM chapter for endocrine, nutritional and metabolic diseases (e00-e89), within the section covering disorders of thyroid gland (e00-e07).

E00.1 is a billable ICD-10-CM code but does not map to a payment HCC under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can be reported on Medicare Advantage encounter data submissions but it does not contribute to a beneficiary's RAF score and therefore does not affect risk-adjusted payments to the plan.

This code does not map to a CMS-HCC V28 payment category. Capture depends on documentation that supports the diagnosis; verify the HCC assignment against the current CMS mapping for the applicable payment year. Coders reviewing E00.1 should check whether additional documentation would support a more specific child code in the same hierarchy that does map to a payment HCC, capturing the correct specificity is the highest-impact RAF improvement available within accurate coding.

HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for E00.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•This code is rarely used in modern developed countries due to iodine supplementation programs; verify documentation clearly states congenital iodine-deficiency syndrome with myxedematous manifestations before coding
•Do not confuse with acquired hypothyroidism (E03.x) or other congenital thyroid disorders; ensure the iodine deficiency etiology is explicitly documented

Clinical Significance

Congenital iodine-deficiency syndrome, myxedematous type, results from severe prenatal and postnatal iodine deficiency leading to profound hypothyroidism with characteristic features including growth retardation, myxedematous facies, dry skin, delayed skeletal maturation, and intellectual disability. Unlike the neurological type, thyroid hormone deficiency predominates. This condition is associated with very high thyroid-stimulating hormone levels and a small or atrophic thyroid gland.

Documentation Requirements

✓Documentation must confirm the myxedematous type of congenital iodine-deficiency syndrome with hypothyroid clinical features (growth retardation, myxedema, delayed bone age), thyroid function tests showing severe hypothyroidism, and history consistent with iodine deficiency.
✓The myxedematous type should be distinguished from the neurological type based on the predominant clinical features.
✓Thyroid replacement therapy and response should be documented.

Commonly Confused Codes

•E00.0 (Neurological type) presents primarily with neurological damage rather than hypothyroid features.
•E03.0 (Congenital hypothyroidism with diffuse goiter) and E03.1 (Congenital hypothyroidism without goiter) capture hypothyroidism from non-iodine-deficiency causes.
•E03.9 (Hypothyroidism, unspecified) lacks the specificity of congenital iodine-deficiency etiology.