What is ICD-10 code E03.5?

E03.5 is the ICD-10-CM diagnosis code for Myxedema coma. A life-threatening emergency condition where severe hypothyroidism causes a coma-like state with dangerously low body temperature, heart rate, and blood pressure. It belongs to the ICD-10-CM chapter for endocrine, nutritional and metabolic diseases (e00-e89). E03.5 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. E03.5 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. E03.5 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. E03.5 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 E03.5 map to under V28?

E03.5 maps to CMS-HCC V28 HCC 202 (Coma, Brain Compression/Anoxic Damage). The category numbers, labels, and conditions come from the CMS-HCC V28 model file for payment year 2026.

What documentation supports E03.5?

This is a medical emergency requiring ICU-level care; always code with appropriate severity indicators and comorbidities Document precipitating factors (infection, medication non-compliance, cold exposure) as these are critical for treatment decisions Because E03.5 maps to an HCC category, the documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment. 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 E03.5: Myxedema coma

E03.5 maps to CMS-HCC V28 202. A source-labeled RAF reference is available. Documentation must support MEAT. MEAT criteria · RAF Calculator · HCC Buddy coding tools

ICD-10-CM Code View

HCC Buddy Code Card

Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.

Code lookupE03.5Effective periodFY2026 Apr Update (Apr 1-Sep 30)

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

E03.5

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

Myxedema coma

A life-threatening emergency condition where severe hypothyroidism causes a coma-like state with dangerously low body temperature, heart rate, and blood pressure.

Buddy Insight

CMS-HCC V28

Mapped

HCC 202

Coma, Brain Compression/Anoxi...

Code-level coefficient reference

CMS-HCC V24

Historical

Not used for standard CY2026 Medicare Advantage payment. Select a historical period to review V24.

Not used for CY2026 payment

ACA/HHS

Mapped

HCC 030

HHS-HCC 030 adult, RAF varies...

Code-level coefficient reference

ESRD/PACE

Mapped

HCC 23

Other Significant Endocrine a...

Code-level coefficient reference

RXHCC

Mapped

HCC 44

Thyroid Disorders

Code-level coefficient reference

Code Book Path

Official

E03Other hypothyroidism

E03.5Myxedema coma

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for E03.5 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for E03.5 in this effective period.

Related Child Codes

Official

E03.0Congenital hypothyroidism with diffuse goiter

E03.1Congenital hypothyroidism without goiter

E03.2Hypothyroidism due to medicaments and other exogenous substances

E03.3Postinfectious hypothyroidism

E03.4Atrophy of thyroid (acquired)

Includes

Official

ICD-10-CM does not list Includes notes for E03.5 in this effective period.

Excludes 1

Official

iodine-deficiency related hypothyroidism (E00-E02)
postprocedural hypothyroidism (E89.0)

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for E03.5 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for E03.5 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for E03.5 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Documentation must clearly establish myxedema coma or crisis with clinical findings including altered mental status, hypothermia, bradycardia, hypotension, and hypoventilation.

Severely deranged thyroid function tests (profoundly elevated thyroid-stimulating hormone, very low or undetectable free thyroxine) must be documented.

The precipitating factor (infection, medication non-adherence, cold exposure, surgery) should be identified.

Treatment with intravenous levothyroxine and/or liothyronine, stress-dose hydrocortisone, and intensive care management should be recorded.

MEAT Support

HCC Buddy guidance

Documentation must clearly establish myxedema coma or crisis with clinical findings including altered mental status, hypothermia, bradycardia, hypotension, and hypoventilation.

Severely deranged thyroid function tests (profoundly elevated thyroid-stimulating hormone, very low or undetectable free thyroxine) must be documented.

The precipitating factor (infection, medication non-adherence, cold exposure, surgery) should be identified.

Treatment with intravenous levothyroxine and/or liothyronine, stress-dose hydrocortisone, and intensive care management should be recorded.

Audit Caution

HCC Buddy guidance

Do not assign this code for severe hypothyroidism without altered mental status or hemodynamic instability

myxedema coma requires end-organ dysfunction. This is an acute, life-threatening condition that should be coded only during the active crisis, not for stable patients with history of prior myxedema coma. Ensure the precipitating cause is identified and coded separately. Do not confuse with hypothyroid myxedema (generalized edema without coma).

Common Mistakes

HCC Buddy guidance

E03.9 (Hypothyroidism, unspecified) captures routine hypothyroidism without the severity of myxedema coma.

E03.8 (Other specified hypothyroidism) does not convey the life-threatening nature of myxedema coma.

R40.20 (Unspecified coma) may be coded concurrently but does not capture the thyroid etiology.

E89.0 (Postprocedural hypothyroidism) identifies a specific etiology that may underlie myxedema coma but does not replace this code.

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 E03.5 an HCC code?

Yes. E03.5 (Myxedema coma) maps to HCC 202, Coma, Brain Compression/Anoxic Damage under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.543. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.

Coder answer: E03.5 is billable and maps to V28 HCC 202, Coma, Brain Compression/Anoxic Damage. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: E03.5
Description: Myxedema coma
HCC (V28): HCC 202 — Coma, Brain Compression/Anoxic Damage
RAF reference coefficient: 0.543
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 202, Coma, Brain Compression/Anoxic Damage

0.543

ESRDHCC 23, Other Significant Endocrine and Metabolic Disorders

Not separately weighted

RxHCCHCC 44, Thyroid Disorders

Not separately weighted

These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. 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 context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.

Work E03.5 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT Criteria for E03.5

For E03.5 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 E03.5 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

E03.5 is the ICD-10-CM diagnosis code for myxedema coma. A life-threatening emergency condition where severe hypothyroidism causes a coma-like state with dangerously low body temperature, heart rate, and blood pressure. E03.5 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).

Under the CMS-HCC V28 risk adjustment model, E03.5 maps to Coma, Brain Compression/Anoxic Damage (HCC 202) with a source-labeled community, non-dual, aged reference coefficient of 0.543. No V24 mapping is shown for E03.5; use the applicable model and payment year when reviewing the V28 mapping. 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. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

This is a medical emergency requiring ICU-level care; always code with appropriate severity indicators and comorbidities. Because E03.5 maps to an HCC category, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment. 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, source-labeled coefficient references, and MEAT documentation criteria for E03.5 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•This is a medical emergency requiring ICU-level care; always code with appropriate severity indicators and comorbidities
•Document precipitating factors (infection, medication non-compliance, cold exposure) as these are critical for treatment decisions

Clinical Significance

Myxedema coma is a life-threatening endocrine emergency representing the most severe form of hypothyroidism, characterized by profound hypothermia, altered mental status progressing to coma, cardiovascular collapse, hypoventilation, and multiorgan dysfunction. Despite the name, true coma may not be present; severe obtundation or lethargy qualifies. Mortality rates range from 20-60% even with aggressive treatment, making rapid recognition and intravenous thyroid hormone replacement critical.

Documentation Requirements

✓Documentation must clearly establish myxedema coma or crisis with clinical findings including altered mental status, hypothermia, bradycardia, hypotension, and hypoventilation.
✓Severely deranged thyroid function tests (profoundly elevated thyroid-stimulating hormone, very low or undetectable free thyroxine) must be documented.
✓The precipitating factor (infection, medication non-adherence, cold exposure, surgery) should be identified.
✓Treatment with intravenous levothyroxine and/or liothyronine, stress-dose hydrocortisone, and intensive care management should be recorded.

Commonly Confused Codes

•E03.9 (Hypothyroidism, unspecified) captures routine hypothyroidism without the severity of myxedema coma.
•E03.8 (Other specified hypothyroidism) does not convey the life-threatening nature of myxedema coma.
•R40.20 (Unspecified coma) may be coded concurrently but does not capture the thyroid etiology.
•E89.0 (Postprocedural hypothyroidism) identifies a specific etiology that may underlie myxedema coma but does not replace this code.