2026 ICD-10-CM Diagnosis Code T38.2X5AAdverse effect of antithyroid drugs, initial encounter

ICD-10-CM Codes›S00–T88›T36-T50›T38

ICD-10-CM T38.2X5A
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

T38.2X5A is a billable ICD-10-CM diagnosis code for adverse effect of antithyroid drugs, initial encounter. The 7th character A marks it as an initial encounter code, used while the patient is receiving active treatment. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 917 through 918. The code is not accepted as a principal diagnosis by the Medicare Code Editor. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Adverse effects of drugs and medicaments, initial encounter.

Code Identity

ICD-10-CM Code
T38.2X5A
Billable Status
Yes — Valid for Submission
Code Describes
Adverse effect of antithyroid drugs, initial encounter
Short Description
Adverse effect of antithyroid drugs, initial encounter
Same as the full description in the CMS dataset.
Parent Code
T38.2X5
Adverse effect of antithyroid drugs

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 CodeT38.2X5AAdverse effect of antithyroid drugs, initial encounter

Code EditsBilling

Medicare Code Editor checks that affect claim validity for T38.2X5A.

Unacceptable principal diagnosis
There are selected codes that describe a circumstance which influences an individual's health status but not a current illness or injury, or codes that are not specific manifestations but may be due to an underlying cause. These codes are considered unacceptable as a principal diagnosis.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Acquired pancytopenia
  • Adverse reaction to thiourea
  • Agranulocytosis
  • Agranulocytosis caused by antithyroid agent
  • Antithyroid drug adverse reaction
  • Carbimazole adverse reaction
  • Hyperthyroidism secondary to potassium iodide
  • Iodine-induced hyperthyroidism
  • Pancytopenia caused by antithyroid drug
  • Pancytopenia caused by medication
  • Post iodine 131 treatment radiation thyroiditis
  • Propylthiouracil adverse reaction
  • Thiouracil antithyroid agent adverse reaction
  • Thyroid disease monitoring status
  • Thyroid drug side effects

Coding GuidelinesGuidance

When coding an adverse effect of a drug that has been correctly prescribed and properly administered, assign the appropriate code for the nature of the adverse effect followed by the appropriate code for the adverse effect of the drug.

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 INJ028
Adverse effects of drugs and medicaments, initial encounter
Default principal diagnosis: inpatient No · outpatient Yes

Clinical InformationClinical

  • Agranulocytosis

    a decrease in the number of granulocytes; (basophils; eosinophils; and neutrophils).

  • Feline Panleukopenia

    a highly contagious dna virus infection of the cat family, characterized by fever, enteritis and bone marrow changes. it is also called feline ataxia, feline agranulocytosis, feline infectious enteritis, cat fever, cat plague, and show fever. it is caused by feline panleukopenia virus or the closely related mink enteritis virus or canine parvovirus.

  • Agranulocytosis

    a marked decrease in the number of mature granulocytes (most often neutrophils) in the peripheral blood.

  • Chemotherapy Related Agranulocytosis|Chemotherapy-Related Agranulocytosis

    agranulocytosis that occurs with chemotherapy.

  • Congenital Neutropenia|congenital neutropenia|genetic infantile agranulocytosis|infantile genetic agranulocytosis

    a rare congenital disorder characterized by mild or severe reduction of neutrophils in the peripheral blood and recurrent infantile infections.

  • Cyclic Neutropenia|CH|CN|Cyclic Agranulocytosis|Cyclic Hematopoiesis|Cyclic Hematopoiesis|Dysplasia, Myelocytic Periodic|Periodic Neutropenia|cyclic neutropenia|periodic neutropenia

    a hematologic disorder caused by a mutation in the elane (ela2) gene; clinical manifestations include recurrent neutropenia with resultant susceptibility to infection leading to fever.

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

Drug Reactions

Most of the time, medicines make our lives better. They reduce aches and pains, fight infections, and control problems such as high blood pressure or diabetes. But medicines can also cause unwanted reactions, such as drug interactions, side effects, and allergies.

The full article covers:

  • What is a drug interaction?
  • What are side effects?
  • What are drug allergies?
  • How can I stay safe when taking medicines?

Read the full article at MedlinePlus

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

Convert T38.2X5A to ICD-9-CMHistory

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

ICD-9-CM
995.29 Adv eff med/biol NEC/NOS
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
E932.8 Adv eff antithyroid agnt
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 T38.2X5AOverview

Is T38.2X5A (Adverse effect of antithyroid drugs) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report adverse effect of antithyroid drugs, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character A in T38.2X5A mean?

The final character A marks the initial encounter: use it while the patient is receiving active treatment for adverse effect of antithyroid drugs, such as an emergency visit or first evaluation.

What MS-DRG does T38.2X5A group to?

On inpatient claims, adverse effect of antithyroid drugs, initial encounter maps to MS-DRG 917, 918, with relative weights from 0.8571 to 1.5684 depending on complications. Higher weights mean higher Medicare reimbursement.

Can T38.2X5A be a principal diagnosis?

No. The Medicare Code Editor rejects this code as a principal diagnosis because adverse effect of antithyroid drugs, initial encounter describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.

What is the ICD-9 equivalent of T38.2X5A?

Under the General Equivalence Mappings, adverse effect of antithyroid drugs, initial encounter converts to ICD-9-CM 995.29 (adv eff med/biol NEC/NOS) and E932.8 (adv eff antithyroid agnt). 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.