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

The ICD-10-CM code for hyperthyroidism when the record documents thyrotoxicosis without an established etiology and without thyrotoxic crisis or storm.

Billable

FY2027

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At a glance

Code Family

E05: Thyrotoxicosis [hyperthyroidism]

DRG Grouping

MS-DRG 643, 644 or 645 under the FY2027 MS-DRG v44 grouper, within MDC 10 for endocrine, nutritional and metabolic diseases and disorders.

HCC Mapping (v28)

None. E05.90 does not map to a CMS-HCC v28 category and contributes no risk adjustment weight.

Condition

Hyperthyroidism

Family Specificity

Category E05 splits first on the documented etiology of the thyrotoxicosis, then on whether thyrotoxic crisis or storm is present. E05.90 is the residual code for an unspecified etiology without crisis.

Billable

Yes. E05.90 is a valid code for HIPAA-covered transactions, and it is unchanged in the FY2027 update effective 1 October 2026.

Which E05 code do I assign?

Category E05 splits on two things at once: the documented cause of the thyrotoxicosis, and whether thyrotoxic crisis or storm is present. E05.90 is correct only when the cause has not been established and no crisis is documented.

When documentation says…

Code

Thyrotoxicosis documented, cause not established, no crisis

E05.90

Thyrotoxicosis without a documented etiology and without thyrotoxic crisis. The note must record thyrotoxicosis or hyperthyroidism as a clinical diagnosis rather than a suppressed TSH standing alone.

Graves' disease

E05.00

Thyrotoxicosis with diffuse goiter, without thyrotoxic crisis or storm. The provider must name Graves' disease or diffuse goiter as the cause. Assign E05.01 where thyroid storm is also documented.

Toxic single thyroid nodule

E05.10

Thyrotoxicosis arising from a single toxic adenoma, without crisis. The note must tie the hyperthyroidism to the nodule. A nodule without hyperthyroidism belongs in category E04 instead.

Toxic multinodular goiter

E05.20

Thyrotoxicosis with toxic multinodular goiter, without crisis. The record must identify the multinodular goiter as the source of the excess thyroid hormone.

Thyroid storm, cause not established

E05.91

Unspecified thyrotoxicosis with thyrotoxic crisis or storm. E05.90 is explicitly the without crisis code. Documented storm rules it out.

Chronic thyroiditis with transient thyrotoxicosis

E06.2

Chronic thyroiditis with transient thyrotoxicosis, an Excludes1 condition at E05. Where it is the documented diagnosis it is coded in place of E05.90, not alongside it. The Index sends hashitoxicosis to E06.3 instead.

Tabular notes

EXCLUDES1

Category E05 carries Excludes1 notes for chronic thyroiditis with transient thyrotoxicosis (E06.2) and for neonatal thyrotoxicosis (P72.1). An Excludes1 note means E05.90 and the excluded code are not reported together for the same condition. Where either is the documented condition, it is assigned in place of E05.90.

USE ADDITIONAL, CODE FIRST AND CODE ALSO

E05.90 carries no use additional, code first or code also instruction in the FY2027 tabular. Associated conditions such as thyrotoxicosis-induced atrial fibrillation are still coded from their own documentation.

FY2027: EFFECTIVE 1 OCTOBER 2026

The FY2027 codes and tabular addenda make no addition, deletion or revision in category E05. The code and its Excludes1 structure are unchanged in the FY2027 tabular effective 1 October 2026.

Operational & financial impact

Why specificity matters beyond the chart: risk adjustment, DRG assignment and denial exposure all follow from which code is selected.

CMS-HCC v28 (PY2024+)

No HCC mapping applies. E05.90 does not map to a Hierarchical Condition Category under CMS-HCC v28 and contributes no risk adjustment factor.

Where the thyrotoxicosis is associated with a condition that does carry HCC weight, that condition must be coded from its own documentation. Atrial fibrillation attributed to thyrotoxicosis is one example. I48.0 and I48.91 map to HCC 238, Specified Heart Arrhythmias, under v28.

MS-DRG v44 (FY2027)

MS-DRG 643: Endocrine Disorders with MCC.

MS-DRG 644: Endocrine Disorders with CC.

MS-DRG 645: Endocrine Disorders without CC/MCC.

As a principal inpatient diagnosis, E05.90 groups within MDC 10, endocrine, nutritional and metabolic diseases and disorders, under the FY2027 MS-DRG v44 grouper. Which of the three tiers applies depends on the complications and comorbidities present on the full claim.

WHERE SPECIFICITY IS LOST

E05.90 is a residual code. Leaving an established cause coded as E05.90 forfeits the clinical detail the specific E05 code carries. Once Graves' disease, a toxic single thyroid nodule or a toxic multinodular goiter is documented, the specific code replaces it.

Medicare and commercial payers

For Medicare, E05.90 supports medical necessity for thyroid function testing including TSH, free T4 and free T3, for thyroid antibody testing, for thyroid ultrasound, for radioiodine uptake scanning and for antithyroid medication management. Coverage of radioactive iodine therapy requires documentation of confirmed hyperthyroidism.

Documentation checklist to support E05.90

Chart elements that support code selection and reduce specificity-driven denials.

Thyrotoxicosis or hyperthyroidism stated by the provider as a clinical diagnosis, not a suppressed TSH result standing on its own.

The laboratory picture behind that diagnosis, such as an elevated free T4 or free T3 with a suppressed TSH.

The clinical findings that support it, such as tachycardia, weight loss, heat intolerance, tremor or anxiety.

Explicit absence of thyrotoxic crisis or storm. Documented storm directs the encounter to E05.91.

The absence of a documented cause. Graves' disease, a toxic single thyroid nodule or a toxic multinodular goiter each direct the encounter to a specific E05 code.

Any thyrotoxicosis-associated atrial fibrillation, documented well enough to be coded alongside E05.90.

A provider query where the record carries findings that point to a specific etiology but no stated cause.

The workup that will establish the etiology, which allows the specific E05 code to replace E05.90 at a later encounter.

FAQ

Is E05.90 a billable code?

Yes. E05.90 is a valid billable ICD-10-CM code for HIPAA-covered transactions in the FY2027 code set, effective 1 October 2026.

When should I use E05.91 instead of E05.90?

Use E05.91 when thyrotoxic crisis or thyroid storm is documented. E05.90 is explicitly the without crisis code. Thyroid storm is a life-threatening emergency, and the distinction has to be confirmed in the record before E05.90 is assigned.

How is E05.90 different from E05.00?

E05.00 is thyrotoxicosis with diffuse goiter without crisis, the code for Graves' disease. E05.90 applies only while the cause remains undocumented. Graves' disease is an inclusion term at E05.0, which directs it to E05.00 rather than E05.90.

Does E05.90 map to a Medicare HCC?

No. E05.90 does not map to a Hierarchical Condition Category under CMS-HCC v28 and carries no risk adjustment weight. Where thyrotoxicosis-induced atrial fibrillation is documented, the atrial fibrillation code carries its own HCC and is reported alongside E05.90.

What does the record have to show to support E05.90?

The record has to show three things: thyrotoxicosis or hyperthyroidism documented by the provider as a clinical diagnosis, the absence of thyrotoxic crisis or storm, and no established etiology. A suppressed TSH without provider interpretation does not support the code.

Does E05.90 work differently for inpatients and outpatients?

The code is the same, but its role differs. Outpatient endocrinology and primary care report E05.90 during thyrotoxicosis workup and management, then move to the specific E05 code as the cause is established. On the inpatient side E05.90 may be a principal or a secondary diagnosis. As principal diagnosis it groups to MS-DRG 643, 644 or 645 within MDC 10 under the FY2027 MS-DRG v44 grouper.

Is E05.90 appropriate for subclinical hyperthyroidism?

ICD-10-CM has no dedicated code for subclinical hyperthyroidism, which presents as a suppressed TSH with a normal free T4. Where the provider documents subclinical hyperthyroidism as the diagnosis, code selection follows what the provider states as the clinical condition. E05.90 or a specific E05 code may apply depending on the etiology.

Did E05.90 change in FY2027?

E05.90 is unchanged in the FY2027 update. The FY2027 update, effective 1 October 2026, makes no addition, deletion or revision in category E05. The code and its Excludes1 structure are unchanged.

Related codes

Codes in the same family as E05.90. Only codes with a published page render as links.

Sibling codes in the E05 family

E05.00: Thyrotoxicosis with diffuse goiter without thyrotoxic crisis or storm.
E05.01: Thyrotoxicosis with diffuse goiter with thyrotoxic crisis or storm.
E05.10: Thyrotoxicosis with toxic single thyroid nodule without thyrotoxic crisis or storm.
E05.20: Thyrotoxicosis with toxic multinodular goiter without thyrotoxic crisis or storm.
E05.80: Other thyrotoxicosis without thyrotoxic crisis or storm.
E05.91: Thyrotoxicosis, unspecified with thyrotoxic crisis or storm.

Additional codes to consider

Codes outside the E05 family considered alongside E05.90.

Consider instead

E05.91: Thyrotoxicosis, unspecified with thyrotoxic crisis or storm, where thyroid storm is documented.
E06.2: Chronic thyroiditis with transient thyrotoxicosis, an Excludes1 condition at E05.
P72.1: Transitory neonatal hyperthyroidism, which governs for neonates under the Excludes1 note for neonatal thyrotoxicosis at E05.
E04.1: Nontoxic single thyroid nodule, where a thyroid nodule is present without thyrotoxicosis.

Sources

All claims on this page derive from government and professional-standards sources.

National Center for Health Statistics. (2026). International classification of diseases, tenth revision, clinical modification (ICD-10-CM) FY2027 files. https://www.cdc.gov/nchs/icd/icd-10-cm/files.html
Centers for Medicare & Medicaid Services and National Center for Health Statistics. (2026). ICD-10-CM official guidelines for coding and reporting FY2027. https://ftp.cdc.gov/pub/Health_Statistics/NCHS/Publications/ICD10CM/2027/ICD-10-CM-October-1-2026-FY27-Guidelines.pdf
Centers for Medicare & Medicaid Services. (2025). 2026 model software/ICD-10 mappings. https://www.cms.gov/medicare/payment/medicare-advantage-rates-statistics/risk-adjustment/2026-model-software-icd-10-mappings
Centers for Medicare & Medicaid Services. (2026). MS-DRG classifications and software, version 44. https://www.cms.gov/medicare/payment/prospective-payment-systems/acute-inpatient-pps/ms-drg-classifications-and-software