2026 ICD-10-CM Diagnosis Code T45.521APoisoning by antithrombotic drugs, accidental (unintentional), initial encounter

ICD-10-CM Codes›S00–T88›T36-T50›T45

ICD-10-CM T45.521A
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

T45.521A is a billable ICD-10-CM diagnosis code for poisoning by antithrombotic drugs, accidental (unintentional), 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. Coders also document this condition as accidental prostaglandin overdose. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under External cause codes: intent of injury, accidental/unintentional; External cause codes: poisoning by drug; and Poisoning by drugs, initial encounter.

Code Identity

ICD-10-CM Code
T45.521A
Billable Status
Yes — Valid for Submission
Code Describes
Poisoning by antithrombotic drugs, accidental (unintentional), initial encounter
Short Description
Poisoning by antithrombotic drugs, accidental, init
Parent Code
T45.521
Poisoning by antithrombotic drugs, accidental (unintentional)

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
CategoryT45Poisoning by, adverse effect of and underdosing of primarily systemic and hematological agents, not elsewhere classified
This CodeT45.521APoisoning by antithrombotic drugs, accidental (unintentional), initial encounter

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Accidental prostaglandin overdose
  • Accidental prostaglandin poisoning
  • Poisoning by prostaglandin
  • Prostaglandin overdose

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 primarily systemic and hematological agents, not elsewhere classified (T45). 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 EXT020
External cause codes: intent of injury, accidental/unintentional
Default principal diagnosis: inpatient No · outpatient No
CCSR EXT014
External cause codes: poisoning by drug
Default principal diagnosis: inpatient No · outpatient No
CCSR INJ022
Poisoning by drugs, initial encounter
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Epoprostenol

    a prostaglandin that is a powerful vasodilator and inhibits platelet aggregation. it is biosynthesized enzymatically from prostaglandin endoperoxides in human vascular tissue. the sodium salt has been also used to treat primary pulmonary hypertension (hypertension, pulmonary).

  • Receptors, Epoprostenol

    cell surface receptors for epoprostenol. they are coupled to heterotrimeric g-proteins.

  • Ticlopidine

    an effective inhibitor of platelet aggregation commonly used in the placement of stents in coronary arteries.

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
AntithromboticT45.521T45.522T45.523T45.524T45.525T45.526
EpoprostenolT45.521T45.522T45.523T45.524T45.525T45.526
IndobufenT45.521T45.522T45.523T45.524T45.525T45.526
ProstacyclinT45.521T45.522T45.523T45.524T45.525T45.526
Prostaglandin (I2)T45.521T45.522T45.523T45.524T45.525T45.526
Prostaglandin (I2)::E1T45.521T45.522T45.523T45.524T45.525T45.526
Prostaglandin (I2)::E2T45.521T45.522T45.523T45.524T45.525T45.526
Prostaglandin (I2)::F2 alphaT45.521T45.522T45.523T45.524T45.525T45.526
TiclopidineT45.521T45.522T45.523T45.524T45.525T45.526
TriflusalT45.521T45.522T45.523T45.524T45.525T45.526

Patient EducationClinical

Medication Errors

Medicines treat infectious diseases, prevent problems from chronic diseases, and ease pain. But medicines can also cause harmful reactions if not used correctly. Errors can happen in the hospital, at the health care provider's office, at the pharmacy, or at home. You can help prevent errors by:

Read the full article at MedlinePlus

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

Convert T45.521A to ICD-9-CMHistory

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

ICD-9-CM
964.2 Poisoning-anticoagulants
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
E858.2 Acc poison-blood agent
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 T45.521AOverview

Is T45.521A a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report poisoning by antithrombotic drugs, accidental (unintentional), initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character A in T45.521A mean?

The final character A marks the initial encounter: use it while the patient is receiving active treatment for poisoning by antithrombotic drugs, accidental (unintentional), such as an emergency visit or first evaluation.

What MS-DRG does T45.521A group to?

When poisoning by antithrombotic drugs, accidental (unintentional), initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 917, 918, with relative weights from 0.8571 to 1.5684 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of T45.521A?

Under the General Equivalence Mappings, poisoning by antithrombotic drugs, accidental (unintentional), initial encounter converts to ICD-9-CM 964.2 (poisoning-anticoagulants) and E858.2 (acc poison-blood agent). 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.