2027 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 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

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 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 951. 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 the other POA exempt codes in Persons with potential health hazards related to family and personal history and certain conditions influencing health status (Z77-Z99).

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to Z91.A3: its own notes plus those printed at Z91, block Z77-Z99, and Chapter 21. A note printed at a category, block or chapter applies to every code under it.

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.

From Z91 Personal risk factors, not elsewhere classified applies to 62 codes
  • contact with and (suspected) exposures hazardous to health (Z77.-)
  • exposure to pollution and other problems related to physical environment (Z77.1-)
  • female genital mutilation status (N90.81-)
  • occupational exposure to risk factors (Z57.-)
  • personal history of physical injury and trauma (Z87.81, Z87.82-)

Code First

The underlying condition named in the note is sequenced before this code.

  • underdosing of medication (T36-T50) with fifth or sixth character 6

Code Also

A second code may be needed to fully describe the condition; the note gives no sequencing direction.

From Block Z77-Z99 Persons with potential health hazards related to family and personal history and certain conditions influencing health status applies to 567 codes
  • any follow-up examination (Z08-Z09)

Notes

General instructions on how these codes are used.

From Chapter 21 (Z00-Z99) Factors influencing health status and contact with health services applies to 1,425 codes
  • Z codes represent reasons for encounters. A corresponding procedure code must accompany a Z code if a procedure is performed. Categories Z00-Z99 are provided for occasions when circumstances other than a disease, injury or external cause classifiable to categories A00-Y89 are recorded as 'diagnoses' or 'problems'. This can arise in two main ways:
  • (a) When a person who may or may not be sick encounters the health services for some specific purpose, such as to receive limited care or service for a current condition, to donate an organ or tissue, to receive prophylactic vaccination (immunization), or to discuss a problem which is in itself not a disease or injury.
  • (b) When some circumstance or problem is present which influences the person's health status but is not in itself a current illness or injury.

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name Z91.A3, its category, or a range that includes it.

Excludes2 1

These codes carry an Excludes2 note naming Z91.A3: its condition is not part of those codes, and both may be reported when the patient has both.

  • Z91.1 Patient's noncompliance with medical treatment and regimen
    caregiver noncompliance with patient's medical treatment and regimen (Z91.A-) names Z91.A-, which includes this code

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

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 2024–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About Z91.A3Overview

What is the ICD-10 code for Caregiver's unintentional underdosing of patient's medication regimen?

The ICD-10-CM code for Caregiver's unintentional underdosing of patient's medication regimen is Z91.A3 (sometimes written as Z91A3). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

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, 2026 through September 30, 2027.

What MS-DRG does Z91.A3 group to?

On inpatient claims, Caregiver's unintentional underdosing of patient's medication regimen maps to MS-DRG 951 (other Factors Influencing Health Status), which carries a relative weight of 0.5574. Higher weights mean higher Medicare reimbursement.

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. The code appears in the Persons with potential health hazards related to family and personal history and certain conditions influencing health status (Z77-Z99) range of the CMS exempt list.