What is ICD-10 code E05.21?

E05.21 is the ICD-10-CM diagnosis code for Thyrotoxicosis with toxic multinodular goiter with thyrotoxic crisis or storm. Overactive thyroid caused by multiple nodules producing excess hormone, with thyroid storm (a severe, life-threatening condition). It belongs to the ICD-10-CM chapter for endocrine, nutritional and metabolic diseases (e00-e89). E05.21 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. E05.21 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. E05.21 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. E05.21 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 E05.21 map to under V28?

E05.21 has no payable CMS-HCC V28 mapping in the final FY2026 CMS file.

What RAF reference is published for E05.21?

E05.21 has no V28 reference coefficient because the final FY2026 source verifies no payable V28 mapping.

What is the V28 vs V24 difference for E05.21?

E05.21 has verified no payable V28 mapping in the final FY2026 source. Select a historical effective period before making any V24 comparison.

What documentation supports E05.21?

This code requires documentation of both multinodular goiter AND thyrotoxic crisis or storm Thyroid storm is a medical emergency; ensure appropriate severity coding and critical care documentation E05.21 is not a CMS-HCC V28 payment code in the verified current source, so MEAT is not the payment hook. Documentation still has to support the diagnosis if you report it.

Can E05.21 be a primary diagnosis?

Yes. E05.21 carries no code-first instruction in the FY2026 tabular, so it can be the first-listed diagnosis when it is the condition chiefly responsible for the encounter and the note supports it, and it can also be reported as a secondary diagnosis. For risk adjustment the order does not matter; the V28 category is the same either way.

Which codes cannot be reported with E05.21?

The Excludes1 note that applies to E05.21 lists transitory endocrine and metabolic disorders specific to newborn (P70-P74); chronic thyroiditis with transient thyrotoxicosis (E06.2); neonatal thyrotoxicosis (P72.1). An Excludes1 condition is not reported together with E05.21; report one or the other, unless the two conditions are unrelated, which the ICD-10-CM Official Guidelines (Section I.A.12.a) allow.

2026 ICD-10-CM E05.21: Thyrotoxicosis with toxic

E05.21 is not a CMS-HCC payment code. MEAT criteria · RAF Calculator · HCC Buddy coding tools

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Code lookupE05.21

Effective periodFY2026 Apr Update (Apr 1-Sep 30)

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

E05.21

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

Thyrotoxicosis with toxic multinodular goiter with thyrotoxic crisis or storm

Overactive thyroid caused by multiple nodules producing excess hormone, with thyroid storm (a severe, life-threatening condition).

Buddy Insight

Thyrotoxicosis with toxic multinodular goiter with thyrotoxic crisis or storm is an acute, life-threatening complication in patients with toxic multinodular goiter.

Overview Risk Models Code Book Documentation Audit Notes Edition comparison

CMS-HCC V28

N/A

—

Not risk-adjusted for this model/period.

Not mapped

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

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 Disorders

Code-level coefficient reference

Code Book Path

Official

E05Thyrotoxicosis [hyperthyroidism]E05.2Thyrotoxicosis with toxic multinodular goiter E05.21Thyrotoxicosis with toxic multinodular goiter with thyrotoxic crisis or storm

Inclusion Terms

Official

Toxic nodular goiter NOSInherited from E05.2

Excludes 2

Official

No Excludes 2 notes are included in this display for E05.21. Check the code and parent instructions in the Code Book.

Related Codes

Official

E05.20Thyrotoxicosis with toxic multinodular goiter without thyrotoxic crisis or storm

Includes

Official

No Includes notes are included in this display for E05.21. Check the code and parent instructions in the Code Book.

Excludes 1

Official

transitory endocrine and metabolic disorders specific to newborn (P70-P74)Inherited from E00-E89, E05
chronic thyroiditis with transient thyrotoxicosis (E06.2)Inherited from E00-E89, E05
neonatal thyrotoxicosis (P72.1)Inherited from E00-E89, E05

Code First

Official

No Code First sequencing instructions are included in this display for E05.21. Check the code and parent instructions in the Code Book.

Use Additional

Official

No Use Additional Code instructions are included in this display for E05.21. Check the code and parent instructions in the Code Book.

Code Also

Official

No Code Also instructions are included in this display for E05.21. Check the code and parent instructions in the Code Book.

Buddy Documentation Tip

HCC Buddy guidance

Documentation must establish both the toxic multinodular goiter etiology and thyrotoxic crisis meeting clinical diagnostic criteria (Burch-Wartofsky Point Scale greater than 45).

Imaging confirming multinodular goiter, thyroid function tests, clinical findings of storm (hyperthermia, severe tachycardia, altered mental status), precipitating factors, and intensive care treatment including antithyroid drugs, beta-blockers, corticosteroids, and supportive care should be documented.

MEAT Support

HCC Buddy guidance

Documentation must establish both the toxic multinodular goiter etiology and thyrotoxic crisis meeting clinical diagnostic criteria (Burch-Wartofsky Point Scale greater than 45).

Audit Caution

HCC Buddy guidance

Ensure documentation supports both the multinodular goiter and the thyrotoxic crisis

neither component alone justifies this code. Do not assign for severe but controlled thyrotoxicosis without documented crisis features. This code should only be used during the acute crisis episode. Age-related comorbidities and cardiac complications should be coded separately. After crisis resolution, transition to E05.20 or a hypothyroidism code as clinically appropriate.

Common Mistakes

HCC Buddy guidance

E05.20 (Thyrotoxicosis with toxic multinodular goiter WITHOUT crisis) captures the stable form.

E05.01 (Thyrotoxicosis with diffuse goiter with crisis) captures storm from Graves disease.

E05.11 (Thyrotoxicosis with toxic single thyroid nodule with crisis) captures storm from a single toxic nodule.

E05.91 (Thyrotoxicosis, unspecified with crisis) is less specific and should not be used when the multinodular etiology is documented.

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 E05.21 an HCC code?

E05.21 is not in the CMS-HCC V28 or V24 community payment model. E05.21 has a separate mapping under the Part D RxHCC model (HCC 44 (Thyroid Disorders)); the applicable result needs member context.

Code: E05.21
Description: Thyrotoxicosis with toxic multinodular goiter with thyrotoxic crisis or storm
HCC (V28): No CMS-HCC V28 mapping
RAF reference coefficient: —
Billable: Yes
Payment year: 2026

HCC Category Mapping

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 E05.21 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for E05.21

For E05.21, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.

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

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What This Code Means

E05.21 is the ICD-10-CM diagnosis code for thyrotoxicosis with toxic multinodular goiter with thyrotoxic crisis or storm. Overactive thyroid caused by multiple nodules producing excess hormone, with thyroid storm (a severe, life-threatening condition). E05.21 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).

E05.21 has no mapping under the CMS-HCC V28 or V24 community payment models. E05.21 has a separate mapping under the Part D RxHCC model (HCC 44 (Thyroid Disorders)); the applicable result needs member context. Do not assign V28 risk adjustment value from this page; verify the applicable model and payment year before using this code for risk adjustment.

This code requires documentation of both multinodular goiter AND thyrotoxic crisis or storm.

HCC Buddy maintains structured V28 and V24 mapping, source-labeled coefficient references, and MEAT documentation criteria for E05.21 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•This code requires documentation of both multinodular goiter AND thyrotoxic crisis or storm
•Thyroid storm is a medical emergency; ensure appropriate severity coding and critical care documentation

Clinical Significance

Thyrotoxicosis with toxic multinodular goiter with thyrotoxic crisis or storm is an acute, life-threatening complication in patients with toxic multinodular goiter. This presentation tends to occur in older patients who may have significant cardiovascular comorbidities, making management particularly challenging. The combination of thyroid storm physiology and age-related cardiovascular vulnerability results in high mortality risk from cardiac arrhythmias, heart failure, and cardiovascular collapse.

Documentation Requirements

✓Documentation must establish both the toxic multinodular goiter etiology and thyrotoxic crisis meeting clinical diagnostic criteria (Burch-Wartofsky Point Scale greater than 45).
✓Imaging confirming multinodular goiter, thyroid function tests, clinical findings of storm (hyperthermia, severe tachycardia, altered mental status), precipitating factors, and intensive care treatment including antithyroid drugs, beta-blockers, corticosteroids, and supportive care should be documented.

Commonly Confused Codes

•E05.20 (Thyrotoxicosis with toxic multinodular goiter WITHOUT crisis) captures the stable form.
•E05.01 (Thyrotoxicosis with diffuse goiter with crisis) captures storm from Graves disease.
•E05.11 (Thyrotoxicosis with toxic single thyroid nodule with crisis) captures storm from a single toxic nodule.
•E05.91 (Thyrotoxicosis, unspecified with crisis) is less specific and should not be used when the multinodular etiology is documented.

Child Codes

E05.20Thyrotoxicosis with toxic multinodular goiter without thyrotoxic crisis or storm

E05.21Thyrotoxicosis with toxic multinodular goiter with thyrotoxic crisis or storm

Code Hierarchy

└E05Thyrotoxicosis [hyperthyroidism]└E05.2Thyrotoxicosis with toxic multinodular goiter └E05.21Thyrotoxicosis with toxic multinodular goiter with thyrotoxic crisis or storm

└E05.21Thyrotoxicosis with toxic multinodular goiter with thyrotoxic crisis or storm

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E05.21

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E05.21 ICD-10-CM Code: Thyrotoxicosis with toxic multinodular goiter with thyrotoxic crisis or storm

HCC Buddy Code Card

E05.21

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MEAT review for E05.21

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What This Code Means

Coding Tips

Clinical Significance

Documentation Requirements

Commonly Confused Codes

Child Codes

Code Hierarchy

Also searched as

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