2026 ICD-10-CM Diagnosis Code T50.Z96AUnderdosing of other vaccines and biological substances, initial encounter

ICD-10-CM Codes›S00–T88›T36-T50›T50

ICD-10-CM T50.Z96A
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

T50.Z96A is a billable ICD-10-CM diagnosis code for underdosing of other vaccines and biological substances, initial encounter. The 7th character A marks it as an initial encounter code, used while the patient is receiving active treatment. 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. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Underdosing of drugs and medicaments, initial encounter.

Code Identity

ICD-10-CM Code
T50.Z96A
Billable Status
Yes — Valid for Submission
Code Describes
Underdosing of other vaccines and biological substances, initial encounter
Short Description
Underdosing of oth vaccines and biological substances, init
Parent Code
T50.Z96
Underdosing of other vaccines and biological substances

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionT36-T50Poisoning by, adverse effect of and underdosing of drugs, medicaments and biological substances
CategoryT50Poisoning by, adverse effect of and underdosing of diuretics and other and unspecified drugs, medicaments and biological substances
This CodeT50.Z96AUnderdosing of other vaccines and biological substances, initial encounter

Code EditsBilling

Medicare Code Editor checks that affect claim validity for T50.Z96A.

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.

Coding GuidelinesGuidance

Underdosing refers to taking less of a medication than is prescribed by a provider or a manufacturer's instruction. Codes for underdosing should never be assigned as principal or first-listed codes. If a patient has a relapse or exacerbation of the medical condition for which the drug is prescribed because of the reduction in dose, then the medical condition itself should be coded.

The appropriate 7th character is to be added to each code from block Poisoning by, adverse effect of and underdosing of diuretics and other and unspecified drugs, medicaments and biological substances (T50). Use the following options for the applicable episode of care:

  • A - initial encounter
  • D - subsequent encounter
  • S - sequela

Source: ICD-10-CM Official Guidelines for Coding and Reporting, FY 2026, published by CMS and the National Center for Health Statistics.

Clinical ClassificationClinical

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

CCSR INJ029
Underdosing of drugs and medicaments, initial encounter
Default principal diagnosis: inpatient No · outpatient No

Table of Drugs and ChemicalsClinical

Substances in the Table of Drugs and Chemicals that reference this code family. Always confirm in the Tabular List before coding.

SubstanceAccidentalSelf-harmAssaultUndeter­minedAdverse
Effect		Under­dosing
Glandular extract (medicinal) NECT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Pegademase, bovineT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NECT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::antineoplasticT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::bacterial NECT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::bacterial NEC::withT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::bacterial NEC::with::other bacterial componentT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::bacterial NEC::with::pertussis componentT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::bacterial NEC::with::viral-rickettsial componentT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::bacterial NEC::mixed NECT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::BCGT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::choleraT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::diphtheriaT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::diphtheria::with tetanusT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::diphtheria::with tetanus::and pertussisT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::influenzaT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::measlesT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::measles::with mumps and rubellaT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::meningococcalT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::mumpsT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::paratyphoidT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::pertussisT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::pertussis::with diphtheriaT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::pertussis::with diphtheria::and tetanusT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::pertussis::with other componentT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::plagueT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::poliomyelitisT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::poliovirusT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::rabiesT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::respiratory syncytial virusT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::rickettsial NECT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::rickettsial NEC::withT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::rickettsial NEC::with::bacterial componentT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::Rocky Mountain spotted feverT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::rubellaT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::sabin oralT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::smallpoxT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::TABT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::tetanusT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::typhoidT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::typhusT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::viral NECT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::yellow feverT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96

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 T50.Z96A to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
No Map There is no ICD-9 equivalent for this code.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About T50.Z96AOverview

Is T50.Z96A (Underdosing of other vaccines and biological substances) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report underdosing of other vaccines and biological substances, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character A in T50.Z96A mean?

The final character A marks the initial encounter: use it while the patient is receiving active treatment for underdosing of other vaccines and biological substances, such as an emergency visit or first evaluation.

Can T50.Z96A be a principal diagnosis?

No. The Medicare Code Editor rejects this code as a principal diagnosis because underdosing of other vaccines and biological substances, initial encounter describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.