2026 ICD-10-CM Diagnosis Code T38.2X4SPoisoning by antithyroid drugs, undetermined, sequela

ICD-10-CM Codes›S00–T88›T36-T50›T38

ICD-10-CM T38.2X4S
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

T38.2X4S is a billable ICD-10-CM diagnosis code for poisoning by antithyroid drugs, undetermined, sequela. The 7th character S marks it as a sequela code, which reports a problem that remains after the original condition has resolved. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 922 through 923. The code is exempt from POA reporting. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Poisoning/toxic effect/adverse effects/underdosing, sequela.

Code Identity

ICD-10-CM Code
T38.2X4S
Billable Status
Yes — Valid for Submission
Code Describes
Poisoning by antithyroid drugs, undetermined, sequela
Short Description
Poisoning by antithyroid drugs, undetermined, sequela
Same as the full description in the CMS dataset.
Parent Code
T38.2X4
Poisoning by antithyroid drugs, undetermined

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionT36-T50Poisoning by, adverse effect of and underdosing of drugs, medicaments and biological substances
CategoryT38Poisoning by, adverse effect of and underdosing of hormones and their synthetic substitutes and antagonists, not elsewhere classified
This CodeT38.2X4SPoisoning by antithyroid drugs, undetermined, sequela

Present on Admission (POA)Billing

T38.2X4S is exempt from POA reporting on inpatient claims to general acute care hospitals. Review other POA exempt codes.

Coding GuidelinesGuidance

When coding a poisoning or reaction to the improper use of a medication (e.g., overdose, wrong substance given or taken in error, wrong route of administration), first assign the appropriate code from categories T36-T50. The poisoning codes have an associated intent as their 5th or 6th character (accidental, intentional self-harm, assault and undetermined). If the intent of the poisoning is unknown or unspecified, code the intent as accidental intent. The undetermined intent is only for use if the documentation in the record specifies that the intent cannot be determined. Use additional code(s) for all manifestations of poisonings.

The appropriate 7th character is to be added to each code from block Poisoning by, adverse effect of and underdosing of hormones and their synthetic substitutes and antagonists, not elsewhere classified (T38). Use the following options for the applicable episode of care:

  • A - initial encounter
  • D - subsequent encounter
  • S - sequela

Source: ICD-10-CM Official Guidelines for Coding and Reporting, FY 2026, published by CMS and the National Center for Health Statistics.

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR INJ075
Poisoning/toxic effect/adverse effects/underdosing, sequela
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Carbimazole

    an imidazole antithyroid agent. carbimazole is metabolized to methimazole, which is responsible for the antithyroid activity.

  • Diiodotyrosine

    a product from the iodination of monoiodotyrosine. in the biosynthesis of thyroid hormones, diiodotyrosine residues are coupled with other monoiodotyrosine or diiodotyrosine residues to form t4 or t3 thyroid hormones (thyroxine and triiodothyronine).

  • Receptors, Thyroid Hormone

    specific high affinity binding proteins for thyroid hormones in target cells. they are usually found in the nucleus and regulate dna transcription. these receptors are activated by hormones that leads to transcription, cell differentiation, and growth suppression. thyroid hormone receptors are encoded by two genes (genes, erba): erba-alpha and erba-beta for alpha and beta thyroid hormone receptors, respectively.

  • Methimazole

    a thioureylene antithyroid agent that inhibits the formation of thyroid hormones by interfering with the incorporation of iodine into tyrosyl residues of thyroglobulin. this is done by interfering with the oxidation of iodide ion and iodotyrosyl groups through inhibition of the peroxidase enzyme.

  • Methylthiouracil

    a thiourea antithyroid agent that inhibits the synthesis of thyroid hormone. it is used in the treatment of hyperthyroidism.

  • Propylthiouracil

    a thiourea antithyroid agent. propythiouracil inhibits the synthesis of thyroxine and inhibits the peripheral conversion of throxine to tri-iodothyronine. it is used in the treatment of hyperthyroidism. (from martindale, the extra pharmacopeoia, 30th ed, p534)

  • Thiourea

    a photographic fixative used also in the manufacture of resins. according to the fourth annual report on carcinogens (ntp 85-002, 1985), this substance may reasonably be anticipated to be a carcinogen (merck index, 9th ed). many of its derivatives are antithyroid agents and/or free radical scavengers.

Table of Drugs and ChemicalsClinical

Substances in the Table of Drugs and Chemicals that reference this code family. Always confirm in the Tabular List before coding.

SubstanceAccidentalSelf-harmAssaultUndeter­minedAdverse
Effect		Under­dosing
Antithyroid drug NECT38.2X1T38.2X2T38.2X3T38.2X4T38.2X5T38.2X6
BenzylthiouracilT38.2X1T38.2X2T38.2X3T38.2X4T38.2X5T38.2X6
CarbimazoleT38.2X1T38.2X2T38.2X3T38.2X4T38.2X5T38.2X6
DiiodotyrosineT38.2X1T38.2X2T38.2X3T38.2X4T38.2X5T38.2X6
IothiouracilT38.2X1T38.2X2T38.2X3T38.2X4T38.2X5T38.2X6
MethiacilT38.2X1T38.2X2T38.2X3T38.2X4T38.2X5T38.2X6
MethimazoleT38.2X1T38.2X2T38.2X3T38.2X4T38.2X5T38.2X6
MethylthiouracilT38.2X1T38.2X2T38.2X3T38.2X4T38.2X5T38.2X6
PropylthiouracilT38.2X1T38.2X2T38.2X3T38.2X4T38.2X5T38.2X6
TapazoleT38.2X1T38.2X2T38.2X3T38.2X4T38.2X5T38.2X6
ThiamazoleT38.2X1T38.2X2T38.2X3T38.2X4T38.2X5T38.2X6
ThiocarbamideT38.2X1T38.2X2T38.2X3T38.2X4T38.2X5T38.2X6
Thiouracil (benzyl) (methyl) (propyl)T38.2X1T38.2X2T38.2X3T38.2X4T38.2X5T38.2X6
ThioureaT38.2X1T38.2X2T38.2X3T38.2X4T38.2X5T38.2X6

Patient EducationClinical

Poisoning

A poison is any substance that is harmful to your body. You might swallow it, inhale it, inject it, or absorb it through your skin. Any substance can be poisonous if too much is taken. Poisons can include:

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert T38.2X4S to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
909.0 Late eff drug poisoning
ApproximateCombination The match is approximate, and more than one code can be needed to describe the source diagnosis. Confirm with contextual judgment.
ICD-9-CM
E989 Late eff inj-undet circ
ApproximateCombination The match is approximate, and more than one code can be needed to describe the source diagnosis. Confirm with contextual judgment.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About T38.2X4SOverview

Is T38.2X4S (Poisoning by antithyroid drugs, undetermined) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report poisoning by antithyroid drugs, undetermined, sequela on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character S in T38.2X4S mean?

The final character S makes this a sequela code: it reports a lingering problem that remains after the poisoning by antithyroid drugs, undetermined itself has resolved, not the original event.

What MS-DRG does T38.2X4S group to?

When poisoning by antithyroid drugs, undetermined, sequela is the principal diagnosis on an inpatient stay, it groups to MS-DRG 922, 923, with relative weights from 1.0177 to 1.7494 depending on complications. Higher weights mean higher Medicare reimbursement.

Is T38.2X4S exempt from POA reporting?

Yes. CMS lists this code among those exempt from present on admission reporting, so hospitals do not assign a POA indicator for poisoning by antithyroid drugs, undetermined, sequela on inpatient claims.

What is the ICD-9 equivalent of T38.2X4S?

Under the General Equivalence Mappings, poisoning by antithyroid drugs, undetermined, sequela converts to ICD-9-CM 909.0 (late eff drug poisoning) and E989 (late eff inj-undet circ). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.