2027 ICD-10-CM Diagnosis Code Z91.128Patient's intentional underdosing of medication regimen for other reason
Z91.128 is a billable ICD-10-CM diagnosis code for Patient's intentional underdosing of medication regimen for other reason. 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. Coders also document this condition as premedication deliberately omitted. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified status.
Code Identity
Code Classification
Code EditsBilling
Medicare Code Editor checks that affect claim validity for Z91.128.
Present on Admission (POA)Billing
Z91.128 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).
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Premedication deliberately omitted
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to Z91.128: its own notes plus those printed at Z91.12, Z91.1, 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.
- caregiver noncompliance with patient's medical treatment and regimen (Z91.A-)
Code First
The underlying condition named in the note is sequenced before this code.
Code Also
A second code may be needed to fully describe the condition; the note gives no sequencing direction.
Notes
General instructions on how these codes are used.
- 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 Z91.128, its category, or a range that includes it.
Use Additional Code 1
These codes say to use an additional code from the note, and Z91.128 is one of the codes named.
- Block T36-T50 Poisoning by, adverse effect of and underdosing of drugs, medicaments and biological substancesunderdosing of medication regimen (Z91.12-, Z91.13-) names Z91.12-, which includes this code
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
medication regimen NEC Z91.148
underdosing See Also: Table of Drugs and Chemicals, categories T36-T50, with final character 6; Z91.148
intentional NEC Z91.128
Underdosing See Also: Table of Drugs and Chemicals, categories T36-T50, with final character 6; Z91.14
intentional NEC Z91.128
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
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 Z91.128 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About Z91.128Overview
Is Z91.128 (Patient's intentional underdosing of medication regimen) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report Patient's intentional underdosing of medication regimen for other reason on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does Z91.128 group to?
On inpatient claims, Patient's intentional underdosing of medication regimen for other reason 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 Z91.128 be a principal diagnosis?
No. The Medicare Code Editor rejects this code as a principal diagnosis because Patient's intentional underdosing of medication regimen for other reason describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.
Is Z91.128 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 Patient's intentional underdosing of medication regimen for other reason 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.
