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E03.9ICD-10-CM

Hypothyroidism, unspecified

BillableMyxedema NOS classifies hereSequenced first for its manifestations

How the code is built

E

Chapter

Endocrine, nutritional and metabolic diseases

03

Category

Other hypothyroidism

9

Char 4

Cause not stated

Chapter

E00 to E89

Endocrine, nutritional and metabolic diseases

Block

E00 to E07

Disorders of thyroid gland

Category

E03

Other hypothyroidism

Billable

Yes

Complete at 4 characters

Inclusion term

Myxedema NOS

The index default for unqualified myxedema

Excludes1 at E03

Two conditions

Iodine-deficiency hypothyroidism and postprocedural hypothyroidism

DefinitionCode structureClinical pictureDocumentationDecision guideTabular listComparisonClaim contextDenialsSources

Key takeaways

  • E03.9 codes hypothyroidism when the provider names no cause for it
  • Assign it only when the record identifies no autoimmune, drug, infectious, atrophic, or surgical origin
  • Myxedema NOS classifies here, and the index routes acquired hypothyroidism and thyroid insufficiency to this code
  • Two Excludes1 conditions block it outright, covering iodine deficiency and hypothyroidism following a procedure
  • It is billable, and it is an etiology code, so it sequences ahead of the conditions it causes
1Definition

What ICD-10 code E03.9 means

E03.9 is the ICD-10-CM code for hypothyroidism, unspecified. It applies when a provider documents hypothyroidism without naming what produced it, which happens routinely when a patient arrives on established levothyroxine therapy and the original workup is not in the chart.

Myxedema NOS classifies here, and the Alphabetic Index routes several everyday phrases to this code, including acquired hypothyroidism, thyroid insufficiency, and low thyroid. What the code does not say is anything about cause, and cause is where nearly all the specificity in this family lives.

Code

E03.9

Descriptor

Hypothyroidism, unspecified

Chapter

Endocrine, nutritional and metabolic diseases

Block

Disorders of thyroid gland

Category

E03, other hypothyroidism

Billable

Yes

Inclusion term

Myxedema NOS

Excludes1 at E03

Iodine-deficiency related hypothyroidism (E00 to E02), postprocedural hypothyroidism (E89.0)

The descriptor has not changed in any fiscal year since 2015. The risk with this code is not a retired reference. It is that the most common cause of hypothyroidism in the United States has its own code in a different category, and the index sends it there rather than here.

2Code structure

Cause sits outside the code, and so does direction

E03.9 has no subdivisions. Two separate structural facts decide whether it is the right code, and the second one surprises people.

The cause axis is spread across four categories

No cause stated

E03.9

This code

Autoimmune, including Hashimoto's

E06.3

Medication or other exogenous substance

E03.2

Postinfectious

E03.3

Acquired thyroid atrophy

E03.4

Congenital, with or without goiter

E03.0, E03.1

Iodine deficiency

E00 to E02, blocked by Excludes1

Following thyroidectomy or radioiodine

E89.0, blocked by Excludes1

Myxedema coma

E03.5

The sequencing direction, which runs opposite to most unspecified codes

Anemia in hypothyroidism

E03.9 first, then D63.8

Cerebral or nervous system degeneration due to hypothyroidism

E03.9 first, then the G32.8 manifestation code

Dementia due to acquired hypothyroidism

E03.9 first, then the dementia-in-diseases-classified-elsewhere code

Myopathy or arthropathy in hypothyroidism

E03.9, with the manifestation coded per the index

This is the fact that distinguishes E03.9 from most unspecified codes. It is not a manifestation waiting behind an underlying disease. It is the underlying disease, and the codes for anemia in chronic disease and for degenerative nervous system disorders both carry code-first instructions naming hypothyroidism across the E00.0 to E03.9 range. When a hypothyroid patient has anemia attributed to the thyroid disorder, the thyroid code leads.

3Clinical picture

Clinical findings documented under E03.9

A record supporting this code describes reduced thyroid hormone effect confirmed on laboratory testing.

General

Fatigue, cold intolerance, weight gain, reduced exercise tolerance

Skin and hair

Dry skin, hair thinning, periorbital or facial puffiness

Gastrointestinal

Constipation

Neuromuscular

Muscle aches, weakness, slowed reflexes, paresthesia

Cognitive and mood

Slowed thinking, poor concentration, low mood

Cardiovascular

Bradycardia, diastolic hypertension, elevated cholesterol

Laboratory

Elevated TSH with low free T4 in overt disease, elevated TSH with normal free T4 in subclinical disease

What keeps an encounter at E03.9 is the absence of a stated cause. Positive thyroid peroxidase antibodies, a documented thyroidectomy, amiodarone or lithium therapy, or a documented iodine deficiency each move the encounter to a different code.

4Documentation

What the chart must show

  • A provider-stated diagnosis of hypothyroidism, not a TSH value alone
  • Thyroid function results, with TSH and free T4 both recorded
  • Antibody testing when performed, since a positive result names the cause
  • Surgical and radioiodine history, since either one moves the code to E89.0
  • Medication review, since amiodarone, lithium, interferon, and checkpoint inhibitors each cause hypothyroidism
  • Whether the disease is overt or subclinical
  • Current thyroid hormone replacement and the monitoring plan
  • Any condition attributed to the hypothyroidism, stated as caused by it rather than listed nearby

The defect that undermines this code most often is a patient managed on levothyroxine for years with no cause anywhere in the record. The diagnosis is real, the code is defensible on its face, and a single antibody result or an operative history would replace it with something specific.

5Decision guide

When to assign E03.9, and when not to

Hypothyroidism, no cause stated

E03.9

Myxedema, unqualified

E03.9

Hashimoto's thyroiditis, or autoimmune hypothyroidism

E06.3

Hypothyroidism after thyroidectomy or radioiodine

E89.0, never E03.9

Hypothyroidism from amiodarone, lithium, or another drug

E03.2, with the adverse effect code

Hypothyroidism following thyroiditis of infectious origin

E03.3

Acquired atrophy of the thyroid

E03.4

Congenital hypothyroidism

E03.0 or E03.1

Myxedema coma

E03.5

Iodine-deficiency hypothyroidism

E00 to E02, never E03.9

Subclinical hypothyroidism, not iodine-related

E03.9

Hypothyroidism in pregnancy

The obstetric code first, then E03.9

Elevated TSH with no diagnosis stated

Query, since a lab value is not a diagnosis

Sequencing follows one rule that runs against the pattern on most unspecified-code pages. E03.9 is an etiology code. When the record attributes anemia, a degenerative nervous system disorder, or dementia to the hypothyroidism, E03.9 is sequenced first, and the manifestation follows.

Query rather than default when the chart holds antibody results, a thyroid surgical history, radioiodine treatment, or a medication known to suppress thyroid function that the assessment never connected to the diagnosis.

6Tabular list

Instructional notes at E03 and above

Inclusion term at E03.9

Myxedema NOS

Excludes1 at E03

Iodine-deficiency related hypothyroidism (E00 to E02)

Excludes1 at E03

Postprocedural hypothyroidism (E89.0)

Excludes1 at E00 to E89

Transitory endocrine and metabolic disorders specific to newborn (P70 to P74)

Excludes1 at L98.5

Myxedema (E03.9), so skin mucinosis and myxedema are never reported together

Code first at D63.8 and G32.8

Hypothyroidism across E00.0 to E03.9, as the underlying disease

Both notes at E03 are Excludes1, which makes them prohibitions rather than permissions. That matters most for postprocedural hypothyroidism. A patient who becomes hypothyroid after a thyroidectomy or after radioiodine ablation does not get E03.9 at all. The condition is classified as E89.0, and reporting E03.9 instead misstates a surgical outcome as an idiopathic disease.

The iodine-deficiency exclusion carries a subtler consequence. Subclinical hypothyroidism has a dedicated code only in its iodine-deficiency form, at E02. Subclinical disease from any other cause has no code of its own, so it reports to E03.9 unless the underlying cause is documented.

7Comparison

Codes frequently confused with E03.9

E06.3

Descriptor

Autoimmune thyroiditis

Use instead when

Hashimoto's, lymphocytic thyroiditis, or autoimmune hypothyroidism is documented

E89.0

Descriptor

Postprocedural hypothyroidism

Use instead when

Hypothyroidism follows thyroid surgery or radioiodine

E03.2

Descriptor

Hypothyroidism due to medicaments and other exogenous substances

Use instead when

A drug caused the hypothyroidism

E03.3

Descriptor

Postinfectious hypothyroidism

Use instead when

An infection caused it

E03.4

Descriptor

Atrophy of thyroid (acquired)

Use instead when

Acquired thyroid atrophy is documented

E03.0, E03.1

Descriptor

Congenital hypothyroidism with diffuse goiter, and without goiter

Use instead when

The condition is congenital

E03.5

Descriptor

Myxedema coma

Use instead when

Decompensated hypothyroidism with altered consciousness is documented

E03.8

Descriptor

Other specified hypothyroidism

Use instead when

A cause is named but has no dedicated code

E00.-

Descriptor

Congenital iodine-deficiency syndrome

Use instead when

Congenital iodine deficiency is documented

E01.-

Descriptor

Iodine-deficiency related thyroid disorders and allied conditions

Use instead when

Acquired iodine deficiency is documented

E02

Descriptor

Subclinical iodine-deficiency hypothyroidism

Use instead when

Subclinical disease is attributed to iodine deficiency

E06.-

Descriptor

Thyroiditis, other forms

Use instead when

Acute, subacute, drug-induced, or unspecified thyroiditis is documented

E04.-

Descriptor

Other nontoxic goiter

Use instead when

Goiter is the diagnosis rather than thyroid hormone deficiency

E05.-

Descriptor

Thyrotoxicosis

Use instead when

Thyroid function is elevated rather than reduced

E07.9

Descriptor

Disorder of thyroid, unspecified

Use instead when

A thyroid disorder is documented without direction

L98.5

Descriptor

Mucinosis of the skin

Use instead when

Skin mucinosis is the diagnosis, which the Excludes1 separates from myxedema

D63.8

Descriptor

Anemia in other chronic diseases classified elsewhere

Use instead when

Anemia is attributed to the hypothyroidism, reported after E03.9

The E06.3 relationship is the most consequential row in this table. Autoimmune thyroiditis is the leading cause of hypothyroidism in the United States, and the Alphabetic Index routes autoimmune hypothyroidism to E06.3 rather than to E03. E06.3 already carries the hypothyroid state, so adding E03.9 alongside it reports the same condition twice at two levels of specificity.

8Claim context

Services commonly reported with E03.9

E03.9 is a high-volume chronic diagnosis in primary care and endocrinology. It supports office evaluation and management, the thyroid function testing that monitors replacement therapy, and thyroid ultrasound when nodularity or gland enlargement is documented.

Laboratory frequency is where the friction sits. Coverage policies for thyroid function testing set expectations for how often TSH and free T4 are reasonable in a stable patient on a steady dose, and testing more often than the policy contemplates needs documentation explaining why, such as a recent dose change, pregnancy, or a new symptom. The diagnosis code alone rarely carries that justification.

When the patient is on long-term thyroid hormone replacement, report the applicable long-term drug therapy status code alongside the diagnosis. Confirm the applicable local coverage determination before submitting repeat testing or imaging.

9Denials

Coding errors that cause denials

Coding E03.9 when Hashimoto's or autoimmune thyroiditis is documented

Assign E06.3, which already includes the hypothyroid state

Reporting E03.9 and E06.3 together for the same condition

Report E06.3 alone, since the pair duplicates one diagnosis

Coding E03.9 for hypothyroidism after thyroidectomy or radioiodine

Assign E89.0, since the Excludes1 blocks E03.9

Coding E03.9 for iodine-deficiency hypothyroidism

Assign the applicable code from E00 to E02

Missing the drug cause when amiodarone, lithium, or a checkpoint inhibitor is on the medication list

Assign E03.2 with the adverse effect code

Sequencing a manifestation ahead of E03.9

Sequence E03.9 first, since it is the underlying disease

Assigning E03.9 from an elevated TSH with no stated diagnosis

Query, since a lab value does not establish the diagnosis

Coding E03.9 alone for a pregnant patient

Sequence the obstetric code first

Billing frequent thyroid testing without a documented reason

Record the dose change, pregnancy, or new symptom prompting the test

10Sources

Where to verify E03.9

ICD-10-CM Official Guidelines for Coding and Reporting

Etiology and manifestation sequencing, and the rules on coding from abnormal findings

The ICD-10-CM Tabular List at E03, E06, and E89

The two Excludes1 notes, the Myxedema NOS inclusion term, and the postprocedural classification

The CMS ICD-10 code page

Current code files and the annual addenda

NCD 190.22, Thyroid Testing

Frequency criteria and the covered diagnosis list for thyroid function studies

Local coverage determinations from the applicable MAC

Indications for thyroid ultrasound

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Last reviewed August 2026

This page is a free reference for billing and coding teams and is not coding, legal, or clinical advice. Code selection depends on the documentation in the record and on the policy of the payer being billed. Verify every code, instructional note, and sequencing rule against the current ICD-10-CM files and the Official Guidelines for Coding and Reporting for the applicable date of service. ICD-10-CM is maintained by the CDC's National Center for Health Statistics and published by CMS. CPT is a registered trademark of the American Medical Association. TruCare is not affiliated with CMS, NCHS, the AHA, or the AMA.

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