Z91.138 ICD-10-CM Code: Patient's unintentional underdosing of medication regimen for other reason
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FY 2026 Apr update / Factors influencing health status and contact with health services (Z00-Z99) / Persons with potential health hazards related to family and personal history and certain conditions influencing health status (Z77-Z99)
Z91.138
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidancePatient's unintentional underdosing of medication regimen for other reason
A patient unintentionally takes less medication than prescribed for reasons other than age-related debility, such as forgetfulness, confusion, or physical inability to take medications.
CMS-HCC V28
00
RAF 0
CMS-HCC V24
00
RAF 0
ACA/HHS
00
RAF 0
ESRD/PACE
00
RAF 0
RXHCC
00
RAF 0
Code Trumping
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Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for Z91.138 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for Z91.138 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for Z91.138 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for Z91.138 in this effective period.
Code First
Official- underdosing of medication (T36-T50) with fifth or sixth character 6
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for Z91.138 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for Z91.138 in this effective period.
Buddy Documentation Tip
Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.
Is Z91.138 an HCC code?
No. Z91.138 is a billable ICD-10-CM code but does not map to any HCC category in V28, V24, ESRD, or RxHCC.
This code does not map to an HCC category in any model (V28, V24, ESRD, RxHCC).
What This Code Means
Z91.138 is the ICD-10-CM diagnosis code for patient's unintentional underdosing of medication regimen for other reason. A patient unintentionally takes less medication than prescribed for reasons other than age-related debility, such as forgetfulness, confusion, or physical inability to take medications. Z91.138 sits in the ICD-10-CM chapter for factors influencing health status and contact with health services (z00-z99), within the section covering persons with potential health hazards related to family and personal history and certain conditions influencing health status (z77-z99).
Z91.138 is a billable ICD-10-CM code but does not map to a payment HCC under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can be reported on Medicare Advantage encounter data submissions but it does not contribute to a beneficiary's RAF score and therefore does not affect risk-adjusted payments to the plan.
Distinguish between intentional and unintentional underdosing; this code is for unintentional cases.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for Z91.138 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Distinguish between intentional and unintentional underdosing; this code is for unintentional cases
- •Document the specific reason for unintentional underdosing to guide intervention strategies