2026 ICD-10-CM Diagnosis Code Z91.A3Caregiver's unintentional underdosing of patient's medication regimen

ICD-10-CM Codes›Z00–Z99›Z77-Z99›Z91

ICD-10-CM Z91.A3
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

Z91.A3 is a billable ICD-10-CM diagnosis code for Caregiver's unintentional underdosing of patient's medication regimen. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026). The code is not accepted as a principal diagnosis by the Medicare Code Editor and exempt from POA reporting. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified status.

Code Identity

ICD-10-CM Code
Z91.A3
Billable Status
Yes — Valid for Submission
Code Describes
Caregiver's unintentional underdosing of patient's medication regimen
Short Description
Carers unintent underdosing of patient's medication regimen
Parent Code
Z91.A
Caregiver's noncompliance with patient's medical treatment and regimen

Code Classification

ChapterZ00–Z99Factors influencing health status and contact with health services
SectionZ77-Z99Persons with potential health hazards related to family and personal history and certain conditions influencing health status
CategoryZ91Personal risk factors, not elsewhere classified
This CodeZ91.A3Caregiver's unintentional underdosing of patient's medication regimen

Code EditsBilling

Medicare Code Editor checks that affect claim validity for Z91.A3.

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.

Present on Admission (POA)Billing

Z91.A3 is exempt from POA reporting on inpatient claims to general acute care hospitals. Review other POA exempt codes.

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Code First

  • underdosing of medication T36 T50

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Noncompliance
      • with
        • medication regimen NEC
          • underdosing
            • unintentional NEC
              • by caregiver

Clinical ClassificationClinical

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

CCSR FAC025
Other specified status
Default principal diagnosis: inpatient No · outpatient Yes

Code History & ChangesHistory

Replacement Z91.A3 replaces the following previously assigned code(s):

  • Z91.19 - Patient's noncompliance w oth medical treatment and regimen
FY 2023AddedAdded to the ICD-10-CM code setEffective October 1, 2022.
FY 2024–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About Z91.A3Overview

Is Z91.A3 a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report Caregiver's unintentional underdosing of patient's medication regimen on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

Can Z91.A3 be a principal diagnosis?

No. The Medicare Code Editor rejects this code as a principal diagnosis because Caregiver's unintentional underdosing of patient's medication regimen describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.

Is Z91.A3 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 Caregiver's unintentional underdosing of patient's medication regimen on inpatient claims.