Z28.3 Underimmunization status
The ICD-10-CM code for Underimmunization status is Z28.3 (FY2026). It is a non-billable category code — select a more specific code below for claims.
Classification
- Section
- Z20-Z29: Persons with potential health hazards related to communicable diseases (Z20-Z29)
- Category Z28
- 23 codes (17 billable)
- FY2026 Status
- Stable since FY2024
U.S. Hospital Utilization
- An estimated 11,030 U.S. inpatient stays in 2022 included Z28.3 among the documented diagnoses.
Source: National Inpatient Sample (NIS), Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality, 2016–2023. National survey-weighted estimates.
Official Coding Guidelines
Z28.3: refer to I.B.14 for documentation guidanceZ28.3 Underimmunization status See Section I.B.14. for underimmunization documentation by clinicians other than the patient’s provider.
List of miscellaneous Z codes with exceptions/notesMiscellaneous Z codes/subcategories/categories: Z28 Immunization not carried out Except: Z28.3-, Underimmunization status Z29 Encounter for other prophylactic measures Z40 Encounter for prophylactic surgery Z41 Encounter for procedures for purposes other than remedying health state Except: Z41.9, Encounter for procedure for purposes other than remedying health state, unspecified Z53 Persons encountering health services for specific procedures and treatment, not carried out Z72 Problems related to lifestyle Note: These codes should be assigned only when the documentation specifies that the patient has an associated problem Z73 Problems related to life management difficulty Note: These codes should be assigned only when the documentation specifies that the patient has an associated problem. Z74 Problems related to care provider dependency Except: Z74.01, Bed confinement status Z75 Problems related to medical facilities and other health care Z76.0 Encounter for issue of repeat prescription
Source: CMS — ICD-10-CM Official Guidelines for Coding and Reporting, FY2026