2027 ICD-10-CM Diagnosis Code T45.AX5SAdverse effect of immune checkpoint inhibitors and immunostimulant drugs, sequela
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 2027 (October 1, 2026 through September 30, 2027) 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
Code Classification
Present on Admission (POA)Billing
T45.AX5S is exempt from POA reporting on inpatient claims to general acute care hospitals. Review the other POA exempt codes in Poisoning by, adverse effect of and underdosing of drugs, medicaments and biological substances (T36-T50).
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 2027, published by CMS and the National Center for Health Statistics.
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to T45.AX5S: its own notes plus those printed at T45.A, T45, block T36-T50, and Chapter 19. A note printed at a category, block or chapter applies to every code under it.
Includes
Further defines, or gives examples of, the content of the category.
- adverse effect of correct substance properly administered
- poisoning by overdose of substance
- poisoning by wrong substance given or taken in error
- underdosing by (inadvertently) (deliberately) taking less substance than prescribed or instructed
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
- poisoning by, adverse effect of and underdosing of antineoplastic and immunosuppressive drug (T45.1)
- toxic reaction to local anesthesia in pregnancy (O29.3-)
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
Code First
The underlying condition named in the note is sequenced before this code.
Use Additional Code
Add a second code, after this one, to fully describe the condition.
- code to identify any retained foreign body, if applicable (Z18.-)
Notes
General instructions on how these codes are used.
- Use secondary code(s) from Chapter 20, External causes of morbidity, to indicate cause of injury. Codes within the T section that include the external cause do not require an additional external cause code
- The chapter uses the S-section for coding different types of injuries related to single body regions and the T-section to cover injuries to unspecified body regions as well as poisoning and certain other consequences of external causes.
7th Character
Every code in the category takes a 7th character from the listed values, with the placeholder X filling any empty positions before it.
- The appropriate 7th character is to be added to each code from category T45
- Ainitial encounter
- Dsubsequent encounter
- Ssequela this code
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name T45.AX5S, its category, or a range that includes it.
Excludes1 1
These codes carry an Excludes1 note naming T45.AX5S: they are not reported together with it, unless the two conditions are unrelated.
Excludes2 1
These codes carry an Excludes2 note naming T45.AX5S: its condition is not part of those codes, and both may be reported when the patient has both.
Use Additional Code 1
These codes say to use an additional code from the note, and T45.AX5S is one of the codes named.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
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.
Code History & ChangesHistory
Replacement T45.AX5S replaces the following previously assigned code(s):
- T45.1X5S - Adverse effect of antineopl and immunosup drugs, sequela
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, 2026 through September 30, 2027.
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 923, 922, with relative weights from 0.9980 to 1.6248 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. The code appears in the Poisoning by, adverse effect of and underdosing of drugs, medicaments and biological substances (T36-T50) range of the CMS exempt list.
Can T45.AX5S be reported with T45.1?
Not as a rule. The Excludes1 note at T45.A, which applies to T45.AX5S, lists "poisoning by, adverse effect of and underdosing of antineoplastic and immunosuppressive drug (T45.1)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).
