2026 ICD-10-CM Diagnosis Code T45.AX5SAdverse effect of immune checkpoint inhibitors and immunostimulant drugs, sequela

ICD-10-CM Codes›S00–T88›T36-T50›T45

ICD-10-CM T45.AX5S
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

T45.AX5S is a billable ICD-10-CM diagnosis code for adverse effect of immune checkpoint inhibitors and immunostimulant drugs, 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. Coders also document this condition as immune checkpoint inhibitor therapy induced enterocolitis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Poisoning/toxic effect/adverse effects/underdosing, sequela.

Code Identity

ICD-10-CM Code
T45.AX5S
Billable Status
Yes — Valid for Submission
Code Describes
Adverse effect of immune checkpoint inhibitors and immunostimulant drugs, sequela
Short Description
Advrs effect of immune chkpt inhibtr/immunostim drugs, sqla
Parent Code
T45.AX5
Adverse effect of immune checkpoint inhibitors and immunostimulant 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
CategoryT45Poisoning by, adverse effect of and underdosing of primarily systemic and hematological agents, not elsewhere classified
This CodeT45.AX5SAdverse effect of immune checkpoint inhibitors and immunostimulant drugs, sequela

Present on Admission (POA)Billing

T45.AX5S is exempt from POA reporting on inpatient claims to general acute care hospitals. Review other POA exempt codes.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Immune checkpoint inhibitor therapy induced enterocolitis

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 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 INJ075
Poisoning/toxic effect/adverse effects/underdosing, sequela
Default principal diagnosis: inpatient No · outpatient Yes

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
ImmuneT45.AX1T45.AX2T45.AX3T45.AX4T45.AX5T45.AX6
Immune::checkpoint inhibitorsT45.AX1T45.AX2T45.AX3T45.AX4T45.AX5T45.AX6
Immune::globulinT45.AX1T45.AX2T45.AX3T45.AX4T45.AX5T45.AX6
Immune::serum globulinT45.AX1T45.AX2T45.AX3T45.AX4T45.AX5T45.AX6
Immunostimulant drugT45.AX1T45.AX2T45.AX3T45.AX4T45.AX5T45.AX6

Code History & ChangesHistory

Replacement T45.AX5S replaces the following previously assigned code(s):

  • T45.1X5S - Adverse effect of antineopl and immunosup drugs, sequela
FY 2025AddedAdded to the ICD-10-CM code setEffective October 1, 2024.
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About T45.AX5SOverview

Is T45.AX5S a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report adverse effect of immune checkpoint inhibitors and immunostimulant drugs, sequela on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character S in T45.AX5S mean?

The final character S makes this a sequela code: it reports a lingering problem that remains after the adverse effect of immune checkpoint inhibitors and immunostimulant drugs itself has resolved, not the original event.

What MS-DRG does T45.AX5S group to?

When adverse effect of immune checkpoint inhibitors and immunostimulant drugs, 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 T45.AX5S 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 adverse effect of immune checkpoint inhibitors and immunostimulant drugs, sequela on inpatient claims.

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.