2026 ICD-10-CM Diagnosis Code T46.4X6AUnderdosing of angiotensin-converting-enzyme inhibitors, initial encounter
T46.4X6A is a billable ICD-10-CM diagnosis code for underdosing of angiotensin-converting-enzyme inhibitors, 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
Code Classification
Code EditsBilling
Medicare Code Editor checks that affect claim validity for T46.4X6A.
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 agents primarily affecting the cardiovascular system (T46). 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
Captopril
a potent and specific inhibitor of peptidyl-dipeptidase a. it blocks the conversion of angiotensin i to angiotensin ii, a vasoconstrictor and important regulator of arterial blood pressure. captopril acts to suppress the renin-angiotensin system and inhibits pressure responses to exogenous angiotensin.Cilazapril
one of the angiotensin-converting enzyme inhibitors (ace inhibitors) used for hypertension. it is a prodrug that is hydrolyzed after absorption to its main metabolite cilazaprilat.Enalapril
an angiotensin-converting enzyme inhibitor that is used to treat hypertension and heart failure.Enalaprilat
the active metabolite of enalapril and one of the potent, intravenously administered, angiotensin-converting enzyme inhibitors. it is an effective agent for the treatment of essential hypertension and has beneficial hemodynamic effects in heart failure. the drug produces renal vasodilation with an increase in sodium excretion.Fosinopril
a phosphinic acid-containing angiotensin-converting enzyme inhibitor that is effective in the treatment of hypertension. it is a prodrug that is converted to its active metabolite fosinoprilat.Lisinopril
one of the angiotensin-converting enzyme inhibitors (ace inhibitors), orally active, that has been used in the treatment of hypertension and congestive heart failure.Perindopril
an angiotensin-converting enzyme inhibitor. it is used in patients with hypertension and heart failure.Quinapril
a tetrahydroisoquinoline derivative and angiotensin converting enzyme inhibitor that is used in the treatment of hypertension and heart failure.Ramipril
a long-acting angiotensin-converting enzyme inhibitor. it is a prodrug that is transformed in the liver to its active metabolite ramiprilat.
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
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 T46.4X6A to ICD-9-CMHistory
Code HistoryHistory
Questions About T46.4X6AOverview
Is T46.4X6A (Underdosing of angiotensin-converting-enzyme inhibitors) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report underdosing of angiotensin-converting-enzyme inhibitors, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T46.4X6A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for underdosing of angiotensin-converting-enzyme inhibitors, such as an emergency visit or first evaluation.
Can T46.4X6A be a principal diagnosis?
No. The Medicare Code Editor rejects this code as a principal diagnosis because underdosing of angiotensin-converting-enzyme inhibitors, 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.
