Skip to content
HCC Buddy home

E05.91 ICD-10-CM Code: Thyrotoxicosis, unspecified with thyrotoxic crisis or storm

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.

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

E05.91

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

Thyrotoxicosis, unspecified with thyrotoxic crisis or storm

Overactive thyroid of unknown or unspecified cause, with thyroid storm (severe, life-threatening condition).

Buddy the Bee presenting code insight

Buddy Insight

Unspecified thyrotoxicosis with thyrotoxic crisis represents thyroid storm of unknown etiology, a life-threatening emergency requiring immediate intervention regardless of the underlying cause.

CMS-HCC V28

0

0

RAF 0

CMS-HCC V24

0

0

RAF 0

ACA/HHS

0

0

RAF 0

ESRD/PACE

0

0

RAF 0

RXHCC

HCC 44

RAF 0.0

Code Trumping

Basket needed

Code Book Path

Official
E05Thyrotoxicosis [hyperthyroidism]
E05.9Thyrotoxicosis, unspecified
E05.91Thyrotoxicosis, unspecified with thyrotoxic crisis or storm

Inclusion Terms

Official
  • Hyperthyroidism NOS

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for E05.91 in this effective period.

Related Child Codes

Official
E05.90Thyrotoxicosis, unspecified without thyrotoxic crisis or storm

Includes

Official

ICD-10-CM does not list Includes notes for E05.91 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for E05.91 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for E05.91 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for E05.91 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for E05.91 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance
Document clinical criteria for thyroid storm (Burch-Wartofsky score), vital signs demonstrating systemic decompensation, altered mental status, and the interventions initiated.
State that the specific etiology of thyrotoxicosis has not yet been determined.
Record critical care time, beta-blocker therapy, iodine administration, and glucocorticoid use.

MEAT Support

HCC Buddy guidance
Document clinical criteria for thyroid storm (Burch-Wartofsky score), vital signs demonstrating systemic decompensation, altered mental status, and the interventions initiated.
State that the specific etiology of thyrotoxicosis has not yet been determined.
Record critical care time, beta-blocker therapy, iodine administration, and glucocorticoid use.

Audit Caution

HCC Buddy guidance
Once the etiology is determined (often after the acute crisis stabilizes), update subsequent encounter codes to the specific thyrotoxicosis category.
The unspecified code is appropriate for the initial emergency presentation but should not persist once diagnostic workup is complete.

Common Mistakes

HCC Buddy guidance
E05.90: Thyrotoxicosis unspecified WITHOUT crisis — use when storm criteria are not present
E05.01: Thyrotoxicosis with diffuse goiter with crisis — use when Graves disease is confirmed
E05.81: Other thyrotoxicosis with crisis — use when a specific uncommon etiology is identified

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 E05.91 an HCC code?

No. E05.91 is a billable ICD-10-CM code but does not map to any HCC category in V28, V24, ESRD, or RxHCC.

HCC Category Mapping

RxHCCHCC 44, Thyroid and Parathyroid Disorders
0.000

RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. 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.

MEAT Criteria for E05.91

For E05.91to 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 E05.91 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

Get the V28 RAF + MEAT cheat sheet

One printable page: confirm a code's V28 HCC status, its RAF weight, and the MEAT your note needs to make it stick. Free, no card.

Free PDF. No card. Unsubscribe anytime.

What This Code Means

E05.91 is the ICD-10-CM diagnosis code for thyrotoxicosis, unspecified with thyrotoxic crisis or storm. Overactive thyroid of unknown or unspecified cause, with thyroid storm (severe, life-threatening condition). E05.91 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).

E05.91 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.

Maps to RxHCC 44 (Osteoporosis, Vertebral and Pathological Fractures) in the prescription drug model. Despite the critical care acuity, this code does not map to CMS-HCC v28 or v24 models. The RxHCC mapping captures drug utilization costs for thyroid storm management.

HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for E05.91 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •This code indicates thyroid storm without a documented cause; attempt to identify the underlying cause
  • •Ensure critical care and emergency codes are assigned appropriately

Clinical Significance

Unspecified thyrotoxicosis with thyrotoxic crisis represents thyroid storm of unknown etiology, a life-threatening emergency requiring immediate intervention regardless of the underlying cause. The unspecified nature reflects the emergent clinical scenario where treatment must begin before diagnostic workup can determine the specific cause. Mortality rates for thyroid storm range from 10-30%, making rapid identification and treatment paramount.

Documentation Requirements

  • ✓Document clinical criteria for thyroid storm (Burch-Wartofsky score), vital signs demonstrating systemic decompensation, altered mental status, and the interventions initiated.
  • ✓State that the specific etiology of thyrotoxicosis has not yet been determined.
  • ✓Record critical care time, beta-blocker therapy, iodine administration, and glucocorticoid use.

Commonly Confused Codes

  • •E05.90: Thyrotoxicosis unspecified WITHOUT crisis: use when storm criteria are not present
  • •E05.01: Thyrotoxicosis with diffuse goiter with crisis: use when Graves disease is confirmed
  • •E05.81: Other thyrotoxicosis with crisis: use when a specific uncommon etiology is identified

Child Codes

E05.90Thyrotoxicosis, unspecified without thyrotoxic crisis or storm
E05.91Thyrotoxicosis, unspecified with thyrotoxic crisis or storm

Code Hierarchy

└E05Thyrotoxicosis [hyperthyroidism]└E05.9Thyrotoxicosis, unspecified└E05.91Thyrotoxicosis, unspecified with thyrotoxic crisis or storm
└E05.91Thyrotoxicosis, unspecified with thyrotoxic crisis or storm

Work E05.91 in HCC Buddy

Open E05.91 in the Code Book for the full Index-to-Tabular path, MEAT checklist, and V28 HCC mapping, or in the Encoder to code from a keyword search. Pro includes 14 days to try everything.

Open in Code BookOpen in EncoderStart Pro