2026 ICD-10-CM Diagnosis Code T45.2X5AAdverse effect of vitamins, initial encounter
T45.2X5A is a billable ICD-10-CM diagnosis code for adverse effect of vitamins, 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) and groups to MS-DRG 917 through 918. 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 Adverse effects of drugs and medicaments, initial encounter.
Code Identity
Code Classification
Code EditsBilling
Medicare Code Editor checks that affect claim validity for T45.2X5A.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Adverse reaction to oil
- Adverse reaction to vitamin B and/or vitamin B derivative
- Adverse reaction to vitamin D and/or vitamin D derivative
- Alpha-tocopheryl adverse reaction
- Ascorbic acid adverse reaction
- Calcipotriol adverse reaction
- Fat soluble vitamin adverse reaction
- Fish oils adverse reaction
- Hypercalcemia caused by thiazide and/or retinol
- Intravenous nutrition adverse reaction
- L-Carnitine adverse reaction
- Multivitamin and mineral preparations adverse reaction
- Niacinamide adverse reaction
- Nicotinic acid adverse reaction
- Omega 3-marine triglycerides adverse reaction
- Pyridoxine preparation adverse reaction
- Reticulocyte count outside reference range
- Reticulocytosis
- Reticulocytosis after B12
- Retinoid adverse reaction
- Retinoid dermatitis
- Terpenes adverse reaction
- Thiamine preparation adverse reaction
- Vitamin A adverse reaction
- Vitamin B12 preparation adverse reaction
- Vitamin products adverse reaction
- Water soluble vitamin adverse reaction
Coding GuidelinesGuidance
When coding an adverse effect of a drug that has been correctly prescribed and properly administered, assign the appropriate code for the nature of the adverse effect followed by the appropriate code for the adverse effect of the drug.
The appropriate 7th character is to be added to each code from block Poisoning by, adverse effect of and underdosing of primarily systemic and hematological agents, not elsewhere classified (T45). 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.
Clinical InformationClinical
Reticulocytosis
an increase in circulating reticulocytes, which is among the simplest and most reliable signs of accelerated erythrocyte production. reticulocytosis occurs during active blood regeneration (stimulation of red bone marrow) and in certain types of anemia, particularly congenital hemolytic anemia.Reticulocytosis
a laboratory test result indicating an increased number of reticulocytes in the peripheral blood.
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.
Patient EducationClinical
Drug Reactions
Most of the time, medicines make our lives better. They reduce aches and pains, fight infections, and control problems such as high blood pressure or diabetes. But medicines can also cause unwanted reactions, such as drug interactions, side effects, and allergies.
The full article covers:
- What is a drug interaction?
- What are side effects?
- What are drug allergies?
- How can I stay safe when taking medicines?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert T45.2X5A to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T45.2X5AOverview
Is T45.2X5A (Adverse effect of vitamins) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report adverse effect of vitamins, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T45.2X5A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for adverse effect of vitamins, such as an emergency visit or first evaluation.
What MS-DRG does T45.2X5A group to?
On inpatient claims, adverse effect of vitamins, initial encounter maps to MS-DRG 917, 918, with relative weights from 0.8571 to 1.5684 depending on complications. Higher weights mean higher Medicare reimbursement.
Can T45.2X5A be a principal diagnosis?
No. The Medicare Code Editor rejects this code as a principal diagnosis because adverse effect of vitamins, initial encounter describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.
What is the ICD-9 equivalent of T45.2X5A?
Under the General Equivalence Mappings, adverse effect of vitamins, initial encounter converts to ICD-9-CM 995.29 (adv eff med/biol NEC/NOS) and E933.5 (adv eff vitamins NEC). The mapping is approximate, so confirm the match fits the documentation.
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.
